Add the given attributes to this Source. Further calls to withAttributes will not remove these attributes. Note that this operation has no effect on an empty Flow (because the attributes apply only to the contained processing operators).

Aggregate input elements into an arbitrary data structure that can be completed and emitted downstream when custom condition is met which can be triggered by aggregate or timer. It can be thought of a more general groupedWeightedWithin.

Emits when the aggregation function decides the aggregate is complete or the timer function returns true

Backpressures when downstream backpressures and the aggregate is complete

Completes when upstream completes and the last aggregate has been emitted downstream

Cancels when downstream cancels

Attaches the given Sink to this Flow, meaning that elements that passes through will also be sent to the Sink.

It is similar to #wireTap but will backpressure instead of dropping elements when the given Sink is not ready.

Emits when element is available and demand exists both from the Sink and the downstream.

Backpressures when downstream or Sink backpressures

Completes when upstream completes

Cancels when downstream or Sink cancels

Attaches the given Sinks to this Flow, meaning that elements that passes through will also be sent to all those Sinks.

It is similar to #wireTap but will backpressure instead of dropping elements when the given Sinks is not ready.

Emits when element is available and demand exists both from the Sinks and the downstream.

Backpressures when downstream or any of the Sinks backpressures

Completes when upstream completes

Cancels when downstream or any of the Sinks cancels

If the time between the emission of an element and the following downstream demand exceeds the provided timeout, the stream is failed with a akka.stream.BackpressureTimeoutException. The timeout is checked periodically, so the resolution of the check is one period (equals to timeout value).

Emits when upstream emits an element

Backpressures when downstream backpressures

Completes when upstream completes or fails if timeout elapses between element emission and downstream demand.

Cancels when downstream cancels

Allows a faster upstream to progress independently of a slower subscriber by aggregating elements into batches until the subscriber is ready to accept them. For example a batch step might store received elements in an array up to the allowed max limit if the upstream publisher is faster.

This element only rolls up elements if the upstream is faster, but if the downstream is faster it will not duplicate elements.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when downstream stops backpressuring and there is an aggregated element available

Backpressures when there are max batched elements and 1 pending element and downstream backpressures

Completes when upstream completes and there is no batched/pending element waiting

Cancels when downstream cancels

See also SubFlow.conflate, SubFlow.batchWeighted

Allows a faster upstream to progress independently of a slower subscriber by aggregating elements into batches until the subscriber is ready to accept them. For example a batch step might concatenate ByteString elements up to the allowed max limit if the upstream publisher is faster.

This element only rolls up elements if the upstream is faster, but if the downstream is faster it will not duplicate elements.

Batching will apply for all elements, even if a single element cost is greater than the total allowed limit. In this case, previous batched elements will be emitted, then the "heavy" element will be emitted (after being applied with the seed function) without batching further elements with it, and then the rest of the incoming elements are batched.

Emits when downstream stops backpressuring and there is a batched element available

Backpressures when there are max weighted batched elements + 1 pending element and downstream backpressures

Completes when upstream completes and there is no batched/pending element waiting

Cancels when downstream cancels

See also SubFlow.conflate, SubFlow.batch

Adds a fixed size buffer in the flow that allows to store elements from a faster upstream until it becomes full. Depending on the defined akka.stream.OverflowStrategy it might drop elements or backpressure the upstream if there is no space available

Emits when downstream stops backpressuring and there is a pending element in the buffer

Backpressures when downstream backpressures or depending on OverflowStrategy:

• Backpressure - backpressures when buffer is full
• DropHead, DropTail, DropBuffer - never backpressures
• Fail - fails the stream if buffer gets full

Completes when upstream completes and buffered elements has been drained

Cancels when downstream cancels

Transform this stream by applying the given partial function to each of the elements on which the function is defined as they pass through this processing step. Non-matching elements are filtered out.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the provided partial function is defined for the element

Backpressures when the partial function is defined for the element and downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Transform this stream by testing the type of each of the elements on which the element is an instance of the provided type as they pass through this processing step. Non-matching elements are filtered out.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the element is an instance of the provided type

Backpressures when the element is an instance of the provided type and downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

If the completion of the stream does not happen until the provided timeout, the stream is failed with a akka.stream.CompletionTimeoutException.

Emits when upstream emits an element

Backpressures when downstream backpressures

Completes when upstream completes or fails if timeout elapses before upstream completes

Cancels when downstream cancels

Concatenate the given Source to this Flow, meaning that once this Flow’s input is exhausted and all result elements have been generated, the Source’s elements will be produced.

Note that the Source is materialized together with this Flow and is "detached" meaning it will in effect behave as a one element buffer in front of both the sources, that eagerly demands an element on start (so it can not be combined with Source.lazy to defer materialization of that).

The second source is then kept from producing elements by asserting back-pressure until its time comes.

When needing a concat operator that is not detached use #concatLazy

Emits when element is available from current stream or from the given Source when current is completed

Backpressures when downstream backpressures

Completes when given Source completes

Cancels when downstream cancels

Concatenate the given Sources to this Flow, meaning that once this Flow’s input is exhausted and all result elements have been generated, the Source’s elements will be produced.

Note that the Sources are materialized together with this Flow. If lazy materialization is what is needed the operator can be combined with for example Source.lazySource to defer materialization of that until the time when this source completes.

The second source is then kept from producing elements by asserting back-pressure until its time comes.

For a concat operator that is detached, use #concat

If this Flow gets upstream error - no elements from the given Sources will be pulled.

Emits when element is available from current stream or from the given Sources when current is completed

Backpressures when downstream backpressures

Completes when given all those Sources completes

Cancels when downstream cancels

Concatenate the given Source to this Flow, meaning that once this Flow’s input is exhausted and all result elements have been generated, the Source’s elements will be produced.

Note that the Source is materialized together with this Flow. If lazy materialization is what is needed the operator can be combined with for example Source.lazySource to defer materialization of that until the time when this source completes.

The second source is then kept from producing elements by asserting back-pressure until its time comes.

For a concat operator that is detached, use #concat

If this Flow gets upstream error - no elements from the given Source will be pulled.

Emits when element is available from current stream or from the given Source when current is completed

Backpressures when downstream backpressures

Completes when given Source completes

Cancels when downstream cancels

Flatten the sub-flows back into the super-flow by concatenating them. This is usually a bad idea when combined with groupBy since it can easily lead to deadlock—the concatenation does not consume from the second substream until the first has finished and the groupBy operator will get back-pressure from the second stream.

This is identical in effect to mergeSubstreamsWithParallelism(1).

Allows a faster upstream to progress independently of a slower subscriber by conflating elements into a summary until the subscriber is ready to accept them. For example a conflate step might average incoming numbers if the upstream publisher is faster.

This version of conflate does not change the output type of the stream. See SubFlow.conflateWithSeed for a more flexible version that can take a seed function and transform elements while rolling up.

This element only rolls up elements if the upstream is faster, but if the downstream is faster it will not duplicate elements.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when downstream stops backpressuring and there is a conflated element available

Backpressures when never

Completes when upstream completes

Cancels when downstream cancels

see also SubFlow.conflateWithSeed SubFlow.batch SubFlow.batchWeighted

Allows a faster upstream to progress independently of a slower subscriber by conflating elements into a summary until the subscriber is ready to accept them. For example a conflate step might average incoming numbers if the upstream publisher is faster.

This version of conflate allows to derive a seed from the first element and change the aggregated type to be different than the input type. See Flow.conflate for a simpler version that does not change types.

This element only rolls up elements if the upstream is faster, but if the downstream is faster it will not duplicate elements.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when downstream stops backpressuring and there is a conflated element available

Backpressures when never

Completes when upstream completes

Cancels when downstream cancels

see also SubFlow.conflate SubFlow.batch SubFlow.batchWeighted

Shifts elements emission in time by a specified amount. It allows to store elements in internal buffer while waiting for next element to be emitted. Depending on the defined akka.stream.DelayOverflowStrategy it might drop elements or backpressure the upstream if there is no space available in the buffer.

Delay precision is 10ms to avoid unnecessary timer scheduling cycles

Internal buffer has default capacity 16. You can set buffer size by calling withAttributes(inputBuffer)

Emits when there is a pending element in the buffer and configured time for this element elapsed * EmitEarly - strategy do not wait to emit element if buffer is full

Backpressures when depending on OverflowStrategy * Backpressure - backpressures when buffer is full * DropHead, DropTail, DropBuffer - never backpressures * Fail - fails the stream if buffer gets full

Completes when upstream completes and buffered elements has been drained

Cancels when downstream cancels

Shifts elements emission in time by an amount individually determined through delay strategy a specified amount. It allows to store elements in internal buffer while waiting for next element to be emitted. Depending on the defined akka.stream.DelayOverflowStrategy it might drop elements or backpressure the upstream if there is no space available in the buffer.

It determines delay for each ongoing element invoking DelayStrategy.nextDelay(elem: T): FiniteDuration.

Note that elements are not re-ordered: if an element is given a delay much shorter than its predecessor, it will still have to wait for the preceding element before being emitted. It is also important to notice that DelayStrategy can be stateful.

Delay precision is 10ms to avoid unnecessary timer scheduling cycles.

Internal buffer has default capacity 16. You can set buffer size by calling addAttributes(inputBuffer)

Emits when there is a pending element in the buffer and configured time for this element elapsed * EmitEarly - strategy do not wait to emit element if buffer is full

Backpressures when depending on OverflowStrategy * Backpressure - backpressures when buffer is full * DropHead, DropTail, DropBuffer - never backpressures * Fail - fails the stream if buffer gets full

Completes when upstream completes and buffered elements have been drained

Cancels when downstream cancels

Detaches upstream demand from downstream demand without detaching the stream rates; in other words acts like a buffer of size 1.

Emits when upstream emits an element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Attaches the given Sink to this Flow, meaning that elements will be sent to the Sink instead of being passed through if the predicate when returns true.

Emits when emits when an element is available from the input and the chosen output has demand

Backpressures when the currently chosen output back-pressures

Completes when upstream completes and no output is pending

Cancels when any of the downstreams cancel

Discard the given number of elements at the beginning of the stream. No elements will be dropped if n is zero or negative.

Emits when the specified number of elements has been dropped already

Backpressures when the specified number of elements has been dropped and downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Discard elements at the beginning of the stream while predicate is true. All elements will be taken after predicate returns false first time.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when predicate returned false and for all following stream elements

Backpressures when predicate returned false and downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Discard the elements received within the given duration at beginning of the stream.

Emits when the specified time elapsed and a new upstream element arrives

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Allows a faster downstream to progress independently of a slower upstream by extrapolating elements from an older element until new element comes from the upstream. For example an expand step might repeat the last element for the subscriber until it receives an update from upstream.

This element will never "drop" upstream elements as all elements go through at least one extrapolation step. This means that if the upstream is actually faster than the upstream it will be backpressured by the downstream subscriber.

Expand does not support akka.stream.Supervision#restart and akka.stream.Supervision#resume. Exceptions from the expander function will complete the stream with failure.

See also #extrapolate for a version that always preserves the original element and allows for an initial "startup" element.

Emits when downstream stops backpressuring

Backpressures when downstream backpressures or iterator runs empty

Completes when upstream completes

Cancels when downstream cancels

Allows a faster downstream to progress independent of a slower upstream.

This is achieved by introducing "extrapolated" elements - based on those from upstream - whenever downstream signals demand.

Extrapolate does not support akka.stream.Supervision#restart and akka.stream.Supervision#resume. Exceptions from the extrapolate function will complete the stream with failure.

See also #expand for a version that can overwrite the original element.

Emits when downstream stops backpressuring, AND EITHER upstream emits OR initial element is present OR extrapolate is non-empty and applicable

Backpressures when downstream backpressures or current extrapolate runs empty

Completes when upstream completes and current extrapolate runs empty

Cancels when downstream cancels

Allows a faster downstream to progress independent of a slower upstream.

This is achieved by introducing "extrapolated" elements - based on those from upstream - whenever downstream signals demand.

Extrapolate does not support akka.stream.Supervision#restart and akka.stream.Supervision#resume. Exceptions from the extrapolate function will complete the stream with failure.

See also #expand for a version that can overwrite the original element.

Emits when downstream stops backpressuring, AND EITHER upstream emits OR initial element is present OR extrapolate is non-empty and applicable

Backpressures when downstream backpressures or current extrapolate runs empty

Completes when upstream completes and current extrapolate runs empty

Cancels when downstream cancels

Only pass on those elements that satisfy the given predicate.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the given predicate returns true for the element

Backpressures when the given predicate returns true for the element and downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Only pass on those elements that NOT satisfy the given predicate.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the given predicate returns false for the element

Backpressures when the given predicate returns false for the element and downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Transform each input element into a Source of output elements that is then flattened into the output stream by concatenation, fully consuming one Source after the other.

Emits when a currently consumed substream has an element available

Backpressures when downstream backpressures

Completes when upstream completes and all consumed substreams complete

Cancels when downstream cancels

Transform each input element into a Source of output elements that is then flattened into the output stream by merging, where at most breadth substreams are being consumed at any given time.

Emits when a currently consumed substream has an element available

Backpressures when downstream backpressures

Completes when upstream completes and all consumed substreams complete

Cancels when downstream cancels

Takes up to n elements from the stream (less than n only if the upstream completes before emitting n elements), then apply f on these elements in order to obtain a flow, this flow is then materialized and the rest of the input is processed by this flow (similar to via). This method returns a flow consuming the rest of the stream producing the materialized flow's output.

Emits when the materialized flow emits. Notice the first n elements are buffered internally before materializing the flow and connecting it to the rest of the upstream - producing elements at its own discretion (might 'swallow' or multiply elements).

Backpressures when downstream backpressures

Completes when the materialized flow completes. If upstream completes before producing n elements, f will be applied with the provided elements, the resulting flow will be materialized and signalled for upstream completion, it can then complete or continue to emit elements at its own discretion.

Cancels when the materialized flow cancels. Notice that when downstream cancels prior to prefix completion, the cancellation cause is stashed until prefix completion (or upstream completion) and then handed to the materialized flow.

Similar to scan but only emits its result when the upstream completes, after which it also completes. Applies the given function f towards its current and next value, yielding the next current value.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

If the function f throws an exception and the supervision decision is akka.stream.Supervision#restart current value starts at zero again the stream will continue.

Note that the zero value must be immutable.

Emits when upstream completes

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Similar to fold but with an asynchronous function. Applies the given function towards its current and next value, yielding the next current value.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

If the function f returns a failure and the supervision decision is akka.stream.Supervision.Restart current value starts at zero again the stream will continue.

Note that the zero value must be immutable.

Emits when upstream completes

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Chunk up this stream into groups of the given size, with the last group possibly smaller than requested due to end-of-stream.

n must be positive, otherwise IllegalArgumentException is thrown.

Emits when the specified number of elements has been accumulated or upstream completed

Backpressures when a group has been assembled and downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Chunk up this stream into groups of elements that have a cumulative weight greater than or equal to the minWeight, with the last group possibly smaller than requested minWeight due to end-of-stream.

minWeight must be positive, otherwise IllegalArgumentException is thrown. costFn must return a non-negative result for all inputs, otherwise the stage will fail with an IllegalArgumentException.

Emits when the cumulative weight of elements is greater than or equal to the minWeight or upstream completed

Backpressures when a buffered group weighs more than minWeight and downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Chunk up this stream into groups of elements received within a time window, or limited by the weight and number of the elements, whatever happens first. Empty groups will not be emitted if no elements are received from upstream. The last group before end-of-stream will contain the buffered elements since the previously emitted group.

Emits when the configured time elapses since the last group has been emitted or weight limit reached

Backpressures when downstream backpressures, and buffered group (+ pending element) weighs more than maxWeight or has more than maxNumber elements

Completes when upstream completes (emits last group)

Cancels when downstream completes

maxWeight must be positive, maxNumber must be positive, and duration must be greater than 0 seconds, otherwise IllegalArgumentException is thrown.

Chunk up this stream into groups of elements received within a time window, or limited by the weight of the elements, whatever happens first. Empty groups will not be emitted if no elements are received from upstream. The last group before end-of-stream will contain the buffered elements since the previously emitted group.

Emits when the configured time elapses since the last group has been emitted or weight limit reached

Backpressures when downstream backpressures, and buffered group (+ pending element) weighs more than maxWeight

Completes when upstream completes (emits last group)

Cancels when downstream completes

maxWeight must be positive, and duration must be greater than 0 seconds, otherwise IllegalArgumentException is thrown.

Chunk up this stream into groups of elements received within a time window, or limited by the given number of elements, whatever happens first. Empty groups will not be emitted if no elements are received from upstream. The last group before end-of-stream will contain the buffered elements since the previously emitted group.

Emits when the configured time elapses since the last group has been emitted or n elements is buffered

Backpressures when downstream backpressures, and there are n+1 buffered elements

Completes when upstream completes (emits last group)

Cancels when downstream completes

maxNumber must be positive, and duration must be greater than 0 seconds, otherwise IllegalArgumentException is thrown.

If the time between two processed elements exceeds the provided timeout, the stream is failed with a akka.stream.StreamIdleTimeoutException. The timeout is checked periodically, so the resolution of the check is one period (equals to timeout value).

Emits when upstream emits an element

Backpressures when downstream backpressures

Completes when upstream completes or fails if timeout elapses between two emitted elements

Cancels when downstream cancels

Delays the initial element by the specified duration.

Emits when upstream emits an element if the initial delay is already elapsed

Backpressures when downstream backpressures or initial delay is not yet elapsed

Completes when upstream completes

Cancels when downstream cancels

If the first element has not passed through this operator before the provided timeout, the stream is failed with a akka.stream.InitialTimeoutException.

Emits when upstream emits an element

Backpressures when downstream backpressures

Completes when upstream completes or fails if timeout elapses before first element arrives

Cancels when downstream cancels

Interleave is a deterministic merge of the given Source with elements of this Flow. It first emits segmentSize number of elements from this flow to downstream, then - same amount for that source, then repeat process.

Example:

Source(List(1, 2, 3)).interleave(List(4, 5, 6, 7), 2) // 1, 2, 4, 5, 3, 6, 7

After one of upstreams is complete than all the rest elements will be emitted from the second one

If it gets error from one of upstreams - stream completes with failure.

Emits when element is available from the currently consumed upstream

Backpressures when downstream backpressures. Signal to current upstream, switch to next upstream when received segmentSize elements

Completes when the Flow and given Source completes

Cancels when downstream cancels

Interleave is a deterministic merge of the given Sources with elements of this Flow. It first emits segmentSize number of elements from this flow to downstream, then - same amount for that source, then repeat process.

If eagerClose is false and one of the upstreams complete the elements from the other upstream will continue passing through the interleave operator. If eagerClose is true and one of the upstream complete interleave will cancel the other upstream and complete itself.

If it gets error from one of upstreams - stream completes with failure.

Emits when element is available from the currently consumed upstream

Backpressures when downstream backpressures. Signal to current upstream, switch to next upstream when received segmentSize elements

Completes when the Flow and given Source completes

Cancels when downstream cancels

Intersperses stream with provided element, similar to how scala.collection.immutable.List.mkString injects a separator between a List's elements.

Additionally can inject start and end marker elements to stream.

Examples:

Source<Integer, ?> nums = Source.from(Arrays.asList(0, 1, 2, 3));
nums.intersperse(",");            //   1 , 2 , 3
nums.intersperse("[", ",", "]");  // [ 1 , 2 , 3 ]

Emits when upstream emits (or before with the start element if provided)

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Intersperses stream with provided element, similar to how scala.collection.immutable.List.mkString injects a separator between a List's elements.

Additionally can inject start and end marker elements to stream.

Examples:

Source<Integer, ?> nums = Source.from(Arrays.asList(0, 1, 2, 3));
nums.intersperse(",");            //   1 , 2 , 3
nums.intersperse("[", ",", "]");  // [ 1 , 2 , 3 ]

In case you want to only prepend or only append an element (yet still use the intercept feature to inject a separator between elements, you may want to use the following pattern instead of the 3-argument version of intersperse (See Source.concat for semantics details):

Source.single(">> ").concat(flow.intersperse(","))
flow.intersperse(",").concat(Source.single("END"))

Emits when upstream emits (or before with the start element if provided)

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Injects additional elements if upstream does not emit for a configured amount of time. In other words, this operator attempts to maintains a base rate of emitted elements towards the downstream.

If the downstream backpressures then no element is injected until downstream demand arrives. Injected elements do not accumulate during this period.

Upstream elements are always preferred over injected elements.

Emits when upstream emits an element or if the upstream was idle for the configured period

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Ensure stream boundedness by limiting the number of elements from upstream. If the number of incoming elements exceeds max, it will signal upstream failure StreamLimitException downstream.

Due to input buffering some elements may have been requested from upstream publishers that will then not be processed downstream of this step.

The stream will be completed without producing any elements if n is zero or negative.

Emits when the specified number of elements to take has not yet been reached

Backpressures when downstream backpressures

Completes when the defined number of elements has been taken or upstream completes

Cancels when the defined number of elements has been taken or downstream cancels

See also Flow.take, Flow.takeWithin, Flow.takeWhile

Ensure stream boundedness by evaluating the cost of incoming elements using a cost function. Exactly how many elements will be allowed to travel downstream depends on the evaluated cost of each element. If the accumulated cost exceeds max, it will signal upstream failure StreamLimitException downstream.

Due to input buffering some elements may have been requested from upstream publishers that will then not be processed downstream of this step.

The stream will be completed without producing any elements if n is zero or negative.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the specified number of elements to take has not yet been reached

Backpressures when downstream backpressures

Completes when the defined number of elements has been taken or upstream completes

Cancels when the defined number of elements has been taken or downstream cancels

See also Flow.take, Flow.takeWithin, Flow.takeWhile

Logs elements flowing through the stream as well as completion and erroring.

By default element and completion signals are logged on debug level, and errors are logged on Error level. This can be adjusted according to your needs by providing a custom Attributes.LogLevels attribute on the given Flow.

Uses an internally created LoggingAdapter which uses akka.stream.Log as it's source (use this class to configure slf4j loggers).

Emits when the mapping function returns an element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Logs elements flowing through the stream as well as completion and erroring.

By default element and completion signals are logged on debug level, and errors are logged on Error level. This can be adjusted according to your needs by providing a custom Attributes.LogLevels attribute on the given Flow:

Uses the given LoggingAdapter for logging.

Emits when the mapping function returns an element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Logs elements flowing through the stream as well as completion and erroring.

By default element and completion signals are logged on debug level, and errors are logged on Error level. This can be adjusted according to your needs by providing a custom Attributes.LogLevels attribute on the given Flow:

The extract function will be applied to each element before logging, so it is possible to log only those fields of a complex object flowing through this element.

Uses an internally created LoggingAdapter which uses akka.stream.Log as it's source (use this class to configure slf4j loggers).

Emits when the mapping function returns an element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Logs elements flowing through the stream as well as completion and erroring.

By default element and completion signals are logged on debug level, and errors are logged on Error level. This can be adjusted according to your needs by providing a custom Attributes.LogLevels attribute on the given Flow:

The extract function will be applied to each element before logging, so it is possible to log only those fields of a complex object flowing through this element.

Uses the given LoggingAdapter for logging.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the mapping function returns an element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Logs elements flowing through the stream as well as completion and erroring.

By default element and completion signals are logged on debug level, and errors are logged on Error level. This can be adjusted according to your needs by providing a custom Attributes.LogLevels attribute on the given Flow.

Uses an internally created MarkerLoggingAdapter which uses akka.stream.Log as it's source (use this class to configure slf4j loggers).

Emits when the mapping function returns an element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Logs elements flowing through the stream as well as completion and erroring.

By default element and completion signals are logged on debug level, and errors are logged on Error level. This can be adjusted according to your needs by providing a custom Attributes.LogLevels attribute on the given Flow:

Uses the given MarkerLoggingAdapter for logging.

Emits when the mapping function returns an element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Logs elements flowing through the stream as well as completion and erroring.

By default element and completion signals are logged on debug level, and errors are logged on Error level. This can be adjusted according to your needs by providing a custom Attributes.LogLevels attribute on the given Flow:

The extract function will be applied to each element before logging, so it is possible to log only those fields of a complex object flowing through this element.

Uses an internally created MarkerLoggingAdapter which uses akka.stream.Log as it's source (use this class to configure slf4j loggers).

Emits when the mapping function returns an element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Logs elements flowing through the stream as well as completion and erroring.

By default element and completion signals are logged on debug level, and errors are logged on Error level. This can be adjusted according to your needs by providing a custom Attributes.LogLevels attribute on the given Flow:

The extract function will be applied to each element before logging, so it is possible to log only those fields of a complex object flowing through this element.

Uses the given MarkerLoggingAdapter for logging.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the mapping function returns an element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Transform this stream by applying the given function to each of the elements as they pass through this processing step.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the mapping function returns an element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Transform this stream by applying the given function to each of the elements as they pass through this processing step. The function returns a CompletionStage and the value of that future will be emitted downstream. The number of CompletionStages that shall run in parallel is given as the first argument to mapAsync. These CompletionStages may complete in any order, but the elements that are emitted downstream are in the same order as received from upstream.

If the function f throws an exception or if the CompletionStage is completed with failure and the supervision decision is akka.stream.Supervision#stop the stream will be completed with failure.

If the function f throws an exception or if the CompletionStage is completed with failure and the supervision decision is akka.stream.Supervision#resume or akka.stream.Supervision#restart the element is dropped and the stream continues.

If the CompletionStage is completed with null, it is ignored and the next element is processed.

The function f is always invoked on the elements in the order they arrive.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the CompletionStage returned by the provided function finishes for the next element in sequence

Backpressures when the number of CompletionStages reaches the configured parallelism and the downstream backpressures or the first CompletionStage is not completed

Completes when upstream completes and all CompletionStages has been completed and all elements has been emitted

Cancels when downstream cancels

Transform this stream by applying the given function to each of the elements as they pass through this processing step. The function returns a CompletionStage and the value of that future will be emitted downstream. The number of CompletionStages that shall run in parallel is given as the first argument to mapAsyncUnordered. Each processed element will be emitted downstream as soon as it is ready, i.e. it is possible that the elements are not emitted downstream in the same order as received from upstream.

If the function f throws an exception or if the CompletionStage is completed with failure and the supervision decision is akka.stream.Supervision#stop the stream will be completed with failure.

If the function f throws an exception or if the CompletionStage is completed with failure and the supervision decision is akka.stream.Supervision#resume or akka.stream.Supervision#restart the element is dropped and the stream continues.

The function f is always invoked on the elements in the order they arrive (even though the result of the CompletionStages returned by f might be emitted in a different order).

If the CompletionStage is completed with null, it is ignored and the next element is processed.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when any of the CompletionStages returned by the provided function complete

Backpressures when the number of CompletionStages reaches the configured parallelism and the downstream backpressures

Completes when upstream completes and all CompletionStages have been completed and all elements has been emitted

Cancels when downstream cancels

Transform each input element into an Iterable of output elements that is then flattened into the output stream.

Make sure that the Iterable is immutable or at least not modified after being used as an output sequence. Otherwise the stream may fail with ConcurrentModificationException or other more subtle errors may occur.

The returned Iterable MUST NOT contain null values, as they are illegal as stream elements - according to the Reactive Streams specification.

Emits when the mapping function returns an element or there are still remaining elements from the previously calculated collection

Backpressures when downstream backpressures or there are still remaining elements from the previously calculated collection

Completes when upstream completes and all remaining elements has been emitted

Cancels when downstream cancels

While similar to recover this operator can be used to transform an error signal to a different one *without* logging it as an error in the process. So in that sense it is NOT exactly equivalent to recover(t => throw t2) since recover would log the t2 error.

Since the underlying failure signal onError arrives out-of-band, it might jump over existing elements. This operator can recover the failure signal, but not the skipped elements, which will be dropped.

Similarly to recover throwing an exception inside mapError _will_ be logged.

Emits when element is available from the upstream or upstream is failed and pf returns an element

Backpressures when downstream backpressures

Completes when upstream completes or upstream failed with exception pf can handle

Cancels when downstream cancels

While similar to recover this operator can be used to transform an error signal to a different one *without* logging it as an error in the process. So in that sense it is NOT exactly equivalent to recover(t => throw t2) since recover would log the t2 error.

Since the underlying failure signal onError arrives out-of-band, it might jump over existing elements. This operator can recover the failure signal, but not the skipped elements, which will be dropped.

Similarly to recover throwing an exception inside mapError _will_ be logged.

Emits when element is available from the upstream or upstream is failed and pf returns an element

Backpressures when downstream backpressures

Completes when upstream completes or upstream failed with exception pf can handle

Cancels when downstream cancels

Transform each stream element with the help of a resource.

The resource creation function is invoked once when the stream is materialized and the returned resource is passed to the mapping function for mapping the first element. The mapping function returns a mapped element to emit downstream. The returned T MUST NOT be null as it is illegal as stream element - according to the Reactive Streams specification.

The close function is called only once when the upstream or downstream finishes or fails. You can do some clean-up here, and if the returned value is not empty, it will be emitted to the downstream if available, otherwise the value will be dropped.

Early completion can be done with combination of the takeWhile operator.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

You can configure the default dispatcher for this Source by changing the akka.stream.materializer.blocking-io-dispatcher or set it for a given Source by using ActorAttributes.

Emits when the mapping function returns an element and downstream is ready to consume it

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Merge the given Source to this Flow, taking elements as they arrive from input streams, picking randomly when several elements ready.

Emits when one of the inputs has an element available

Backpressures when downstream backpressures

Completes when all upstreams complete

Cancels when downstream cancels

Merge the given Sources to this Flow, taking elements as they arrive from input streams, picking randomly when several elements ready.

Emits when one of the inputs has an element available

Backpressures when downstream backpressures

Completes when all upstreams complete (eagerComplete=false) or one upstream completes (eagerComplete=true), default value is false

Cancels when downstream cancels

MergeLatest joins elements from N input streams into stream of lists of size N. i-th element in list is the latest emitted element from i-th input stream. MergeLatest emits list for each element emitted from some input stream, but only after each input stream emitted at least one element.

Emits when an element is available from some input and each input emits at least one element from stream start

Completes when all upstreams complete (eagerClose=false) or one upstream completes (eagerClose=true)

Merge two sources. Prefer one source if both sources have elements ready.

emits when one of the inputs has an element available. If multiple have elements available, prefer the 'right' one when 'preferred' is 'true', or the 'left' one when 'preferred' is 'false'.

backpressures when downstream backpressures

completes when all upstreams complete (This behavior is changeable to completing when any upstream completes by setting eagerComplete=true.)

Merge two sources. Prefer the sources depending on the 'priority' parameters.

emits when one of the inputs has an element available, preferring inputs based on the 'priority' parameters if both have elements available

backpressures when downstream backpressures

completes when both upstreams complete (This behavior is changeable to completing when any upstream completes by setting eagerComplete=true.)

Merge the given Source to this Flow, taking elements as they arrive from input streams, picking always the smallest of the available elements (waiting for one element from each side to be available). This means that possible contiguity of the input streams is not exploited to avoid waiting for elements, this merge will block when one of the inputs does not have more elements (and does not complete).

Emits when all of the inputs have an element available

Backpressures when downstream backpressures

Completes when all upstreams complete

Cancels when downstream cancels

Flatten the sub-flows back into the super-flow by performing a merge without parallelism limit (i.e. having an unbounded number of sub-flows active concurrently).

This is identical in effect to mergeSubstreamsWithParallelism(Integer.MAX_VALUE).

Flatten the sub-flows back into the super-flow by performing a merge with the given parallelism limit. This means that only up to parallelism substreams will be executed at any given time. Substreams that are not yet executed are also not materialized, meaning that back-pressure will be exerted at the operator that creates the substreams when the parallelism limit is reached.

onErrorComplete allows to complete the stream when an upstream error occurs.

Since the underlying failure signal onError arrives out-of-band, it might jump over existing elements. This operator can recover the failure signal, but not the skipped elements, which will be dropped.

Emits when element is available from the upstream

Backpressures when downstream backpressures

Completes when upstream completes or failed with predicate return ture

Cancels when downstream cancels

onErrorComplete allows to complete the stream when an upstream error occurs.

Since the underlying failure signal onError arrives out-of-band, it might jump over existing elements. This operator can recover the failure signal, but not the skipped elements, which will be dropped.

Emits when element is available from the upstream

Backpressures when downstream backpressures

Completes when upstream completes or failed with exception is an instance of the provided type

Cancels when downstream cancels

onErrorComplete allows to complete the stream when an upstream error occurs.

Since the underlying failure signal onError arrives out-of-band, it might jump over existing elements. This operator can recover the failure signal, but not the skipped elements, which will be dropped.

Emits when element is available from the upstream

Backpressures when downstream backpressures

Completes when upstream completes or failed with exception is an instance of the provided type

Cancels when downstream cancels

Provides a secondary source that will be consumed if this source completes without any elements passing by. As soon as the first element comes through this stream, the alternative will be cancelled.

Note that this Flow will be materialized together with the Source and just kept from producing elements by asserting back-pressure until its time comes or it gets cancelled.

On errors the operator is failed regardless of source of the error.

Emits when element is available from first stream or first stream closed without emitting any elements and an element is available from the second stream

Backpressures when downstream backpressures

Completes when the primary stream completes after emitting at least one element, when the primary stream completes without emitting and the secondary stream already has completed or when the secondary stream completes

Cancels when downstream cancels and additionally the alternative is cancelled as soon as an element passes by from this stream.

Takes up to n elements from the stream (less than n only if the upstream completes before emitting n elements) and returns a pair containing a strict sequence of the taken element and a stream representing the remaining elements. If n is zero or negative, then this will return a pair of an empty collection and a stream containing the whole upstream unchanged.

In case of an upstream error, depending on the current state

• the master stream signals the error if less than n elements has been seen, and therefore the substream has not yet been emitted
• the tail substream signals the error after the prefix and tail has been emitted by the main stream (at that point the main stream has already completed)

Emits when the configured number of prefix elements are available. Emits this prefix, and the rest as a substream

Backpressures when downstream backpressures or substream backpressures

Completes when prefix elements has been consumed and substream has been consumed

Cancels when downstream cancels or substream cancels

Prepend the given Source to this Flow, meaning that before elements are generated from this Flow, the Source's elements will be produced until it is exhausted, at which point Flow elements will start being produced.

Note that the Source is materialized together with this Flow and is "detached" meaning in effect behave as a one element buffer in front of both the sources, that eagerly demands an element on start (so it can not be combined with Source.lazy to defer materialization of that).

This flow will then be kept from producing elements by asserting back-pressure until its time comes.

When needing a prepend operator that is not detached use #prependLazy

Emits when element is available from the given Source or from current stream when the Source is completed

Backpressures when downstream backpressures

Completes when this Flow completes

Cancels when downstream cancels

Prepend the given Source to this Flow, meaning that before elements are generated from this Flow, the Source's elements will be produced until it is exhausted, at which point Flow elements will start being produced.

Note that the Source is materialized together with this Flow and will then be kept from producing elements by asserting back-pressure until its time comes.

When needing a prepend operator that is also detached use #prepend

If the given Source gets upstream error - no elements from this Flow will be pulled.

Emits when element is available from the given Source or from current stream when the Source is completed

Backpressures when downstream backpressures

Completes when this Flow completes

Cancels when downstream cancels

Recover allows to send last element on failure and gracefully complete the stream Since the underlying failure signal onError arrives out-of-band, it might jump over existing elements. This operator can recover the failure signal, but not the skipped elements, which will be dropped.

Throwing an exception inside recover _will_ be logged on ERROR level automatically.

Emits when element is available from the upstream or upstream is failed and pf returns an element

Backpressures when downstream backpressures

Completes when upstream completes or upstream failed with exception pf can handle

Cancels when downstream cancels

RecoverWith allows to switch to alternative Source on flow failure. It will stay in effect after a failure has been recovered so that each time there is a failure it is fed into the pf and a new Source may be materialized.

Since the underlying failure signal onError arrives out-of-band, it might jump over existing elements. This operator can recover the failure signal, but not the skipped elements, which will be dropped.

Throwing an exception inside recoverWith _will_ be logged on ERROR level automatically.

Emits when element is available from the upstream or upstream is failed and element is available from alternative Source

Backpressures when downstream backpressures

Completes when upstream completes or upstream failed with exception pf can handle

Cancels when downstream cancels

RecoverWithRetries allows to switch to alternative Source on flow failure. It will stay in effect after a failure has been recovered up to attempts number of times so that each time there is a failure it is fed into the pf and a new Source may be materialized. Note that if you pass in 0, this won't attempt to recover at all.

A negative attempts number is interpreted as "infinite", which results in the exact same behavior as recoverWith.

Since the underlying failure signal onError arrives out-of-band, it might jump over existing elements. This operator can recover the failure signal, but not the skipped elements, which will be dropped.

Throwing an exception inside recoverWithRetries _will_ be logged on ERROR level automatically.

Emits when element is available from the upstream or upstream is failed and element is available from alternative Source

Backpressures when downstream backpressures

Completes when upstream completes or upstream failed with exception pf can handle

Cancels when downstream cancels

Similar to fold but uses first element as zero element. Applies the given function towards its current and next value, yielding the next current value.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when upstream completes

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Similar to fold but is not a terminal operation, emits its current value which starts at zero and then applies the current and next value to the given function f, emitting the next current value.

If the function f throws an exception and the supervision decision is akka.stream.Supervision#restart current value starts at zero again the stream will continue.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Note that the zero value must be immutable.

Emits when the function scanning the element returns a new element

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Similar to scan but with a asynchronous function, emits its current value which starts at zero and then applies the current and next value to the given function f, emitting a Future that resolves to the next current value.

If the function f throws an exception and the supervision decision is akka.stream.Supervision.Restart current value starts at zero again the stream will continue.

If the function f throws an exception and the supervision decision is akka.stream.Supervision.Resume current value starts at the previous current value, or zero when it doesn't have one, and the stream will continue.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Note that the zero value must be immutable.

Emits when the future returned by f completes

Backpressures when downstream backpressures

Completes when upstream completes and the last future returned by f completes

Cancels when downstream cancels

See also #scan

Apply a sliding window over the stream and return the windows as groups of elements, with the last group possibly smaller than requested due to end-of-stream.

n must be positive, otherwise IllegalArgumentException is thrown. step must be positive, otherwise IllegalArgumentException is thrown.

Emits when enough elements have been collected within the window or upstream completed

Backpressures when a window has been assembled and downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Transform each stream element with the help of a state.

The state creation function is invoked once when the stream is materialized and the returned state is passed to the mapping function for mapping the first element. The mapping function returns a mapped element to emit downstream and a state to pass to the next mapping function. The state can be the same for each mapping return, be a new immutable state but it is also safe to use a mutable state. The returned T MUST NOT be null as it is illegal as stream element - according to the Reactive Streams specification. A null state is not allowed and will fail the stream.

For stateless variant see map.

The onComplete function is called only once when the upstream or downstream finished, You can do some clean-up here, and if the returned value is not empty, it will be emitted to the downstream if available, otherwise the value will be dropped.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the mapping function returns an element and downstream is ready to consume it

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Transform each input element into an Iterable of output elements that is then flattened into the output stream. The transformation is meant to be stateful, which is enabled by creating the transformation function anew for every materialization — the returned function will typically close over mutable objects to store state between invocations. For the stateless variant see #mapConcat.

Make sure that the Iterable is immutable or at least not modified after being used as an output sequence. Otherwise the stream may fail with ConcurrentModificationException or other more subtle errors may occur.

The returned Iterable MUST NOT contain null values, as they are illegal as stream elements - according to the Reactive Streams specification.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the mapping function returns an element or there are still remaining elements from the previously calculated collection

Backpressures when downstream backpressures or there are still remaining elements from the previously calculated collection

Completes when upstream completes and all remaining elements has been emitted

Cancels when downstream cancels

Terminate processing (and cancel the upstream publisher) after the given number of elements. Due to input buffering some elements may have been requested from upstream publishers that will then not be processed downstream of this step.

The stream will be completed without producing any elements if n is zero or negative.

Emits when the specified number of elements to take has not yet been reached

Backpressures when downstream backpressures

Completes when the defined number of elements has been taken or upstream completes

Cancels when the defined number of elements has been taken or downstream cancels

Terminate processing (and cancel the upstream publisher) after predicate returns false for the first time, including the first failed element iff inclusive is true Due to input buffering some elements may have been requested from upstream publishers that will then not be processed downstream of this step.

The stream will be completed without producing any elements if predicate is false for the first stream element.

Adheres to the ActorAttributes.SupervisionStrategy attribute.

Emits when the predicate is true

Backpressures when downstream backpressures

Completes when predicate returned false (or 1 after predicate returns false if inclusive or upstream completes

Cancels when predicate returned false or downstream cancels

Terminate processing (and cancel the upstream publisher) after predicate returns false for the first time, Due to input buffering some elements may have been requested from upstream publishers that will then not be processed downstream of this step.

The stream will be completed without producing any elements if predicate is false for the first stream element.

Emits when the predicate is true

Backpressures when downstream backpressures

Completes when predicate returned false (or 1 after predicate returns false if inclusive or upstream completes

Cancels when predicate returned false or downstream cancels

Terminate processing (and cancel the upstream publisher) after the given duration. Due to input buffering some elements may have been requested from upstream publishers that will then not be processed downstream of this step.

Note that this can be combined with #take to limit the number of elements within the duration.

Emits when an upstream element arrives

Backpressures when downstream backpressures

Completes when upstream completes or timer fires

Cancels when downstream cancels or timer fires

Sends elements downstream with speed limited to cost/per. Cost is calculating for each element individually by calling calculateCost function. This operator works for streams when elements have different cost(length). Streams of ByteString for example.

Throttle implements the token bucket model. There is a bucket with a given token capacity (burst size or maximumBurst). Tokens drops into the bucket at a given rate and can be spared for later use up to bucket capacity to allow some burstiness. Whenever stream wants to send an element, it takes as many tokens from the bucket as element costs. If there isn't any, throttle waits until the bucket accumulates enough tokens. Elements that costs more than the allowed burst will be delayed proportionally to their cost minus available tokens, meeting the target rate. Bucket is full when stream just materialized and started.

Parameter mode manages behavior when upstream is faster than throttle rate:

• akka.stream.ThrottleMode.Shaping makes pauses before emitting messages to meet throttle rate
• akka.stream.ThrottleMode.Enforcing fails with exception when upstream is faster than throttle rate. Enforcing cannot emit elements that cost more than the maximumBurst

It is recommended to use non-zero burst sizes as they improve both performance and throttling precision by allowing the implementation to avoid using the scheduler when input rates fall below the enforced limit and to reduce most of the inaccuracy caused by the scheduler resolution (which is in the range of milliseconds).

WARNING: Be aware that throttle is using scheduler to slow down the stream. This scheduler has minimal time of triggering next push. Consequently it will slow down the stream as it has minimal pause for emitting. This can happen in case burst is 0 and speed is higher than 30 events per second. You need to increase the maximumBurst if elements arrive with small interval (30 milliseconds or less). Use the overloaded throttle method without maximumBurst parameter to automatically calculate the maximumBurst based on the given rate (cost/per). In other words the throttler always enforces the rate limit when maximumBurst parameter is given, but in certain cases (mostly due to limited scheduler resolution) it enforces a tighter bound than what was prescribed.

Emits when upstream emits an element and configured time per each element elapsed

Backpressures when downstream backpressures or the incoming rate is higher than the speed limit

Completes when upstream completes

Cancels when downstream cancels

Sends elements downstream with speed limited to cost/per. Cost is calculating for each element individually by calling calculateCost function. This operator works for streams when elements have different cost(length). Streams of ByteString for example.

Throttle implements the token bucket model. There is a bucket with a given token capacity (burst size). Tokens drops into the bucket at a given rate and can be spared for later use up to bucket capacity to allow some burstiness. Whenever stream wants to send an element, it takes as many tokens from the bucket as element costs. If there isn't any, throttle waits until the bucket accumulates enough tokens. Elements that costs more than the allowed burst will be delayed proportionally to their cost minus available tokens, meeting the target rate. Bucket is full when stream just materialized and started.

The burst size is calculated based on the given rate (cost/per) as 0.1 * rate, for example: - rate < 20/second => burst size 1 - rate 20/second => burst size 2 - rate 100/second => burst size 10 - rate 200/second => burst size 20

The throttle mode is akka.stream.ThrottleMode.Shaping, which makes pauses before emitting messages to meet throttle rate.

Emits when upstream emits an element and configured time per each element elapsed

Backpressures when downstream backpressures or the incoming rate is higher than the speed limit

Completes when upstream completes

Cancels when downstream cancels

Sends elements downstream with speed limited to elements/per. In other words, this operator set the maximum rate for emitting messages. This operator works for streams where all elements have the same cost or length.

Throttle implements the token bucket model. There is a bucket with a given token capacity (burst size or maximumBurst). Tokens drops into the bucket at a given rate and can be spared for later use up to bucket capacity to allow some burstiness. Whenever stream wants to send an element, it takes as many tokens from the bucket as element costs. If there isn't any, throttle waits until the bucket accumulates enough tokens. Elements that costs more than the allowed burst will be delayed proportionally to their cost minus available tokens, meeting the target rate. Bucket is full when stream just materialized and started.

Parameter mode manages behavior when upstream is faster than throttle rate:

• akka.stream.ThrottleMode.Shaping makes pauses before emitting messages to meet throttle rate
• akka.stream.ThrottleMode.Enforcing fails with exception when upstream is faster than throttle rate

It is recommended to use non-zero burst sizes as they improve both performance and throttling precision by allowing the implementation to avoid using the scheduler when input rates fall below the enforced limit and to reduce most of the inaccuracy caused by the scheduler resolution (which is in the range of milliseconds).

WARNING: Be aware that throttle is using scheduler to slow down the stream. This scheduler has minimal time of triggering next push. Consequently it will slow down the stream as it has minimal pause for emitting. This can happen in case burst is 0 and speed is higher than 30 events per second. You need to increase the maximumBurst if elements arrive with small interval (30 milliseconds or less). Use the overloaded throttle method without maximumBurst parameter to automatically calculate the maximumBurst based on the given rate (cost/per). In other words the throttler always enforces the rate limit when maximumBurst parameter is given, but in certain cases (mostly due to limited scheduler resolution) it enforces a tighter bound than what was prescribed.

Emits when upstream emits an element and configured time per each element elapsed

Backpressures when downstream backpressures or the incoming rate is higher than the speed limit

Completes when upstream completes

Cancels when downstream cancels

Sends elements downstream with speed limited to elements/per. In other words, this operator set the maximum rate for emitting messages. This operator works for streams where all elements have the same cost or length.

Throttle implements the token bucket model. There is a bucket with a given token capacity (burst size). Tokens drops into the bucket at a given rate and can be spared for later use up to bucket capacity to allow some burstiness. Whenever stream wants to send an element, it takes as many tokens from the bucket as element costs. If there isn't any, throttle waits until the bucket accumulates enough tokens. Elements that costs more than the allowed burst will be delayed proportionally to their cost minus available tokens, meeting the target rate. Bucket is full when stream just materialized and started.

The burst size is calculated based on the given rate (cost/per) as 0.1 * rate, for example: - rate < 20/second => burst size 1 - rate 20/second => burst size 2 - rate 100/second => burst size 10 - rate 200/second => burst size 20

The throttle mode is akka.stream.ThrottleMode.Shaping, which makes pauses before emitting messages to meet throttle rate.

Emits when upstream emits an element and configured time per each element elapsed

Backpressures when downstream backpressures or the incoming rate is higher than the speed limit

Completes when upstream completes

Cancels when downstream cancels

Connect this SubFlow to a Sink, concatenating the processing steps of both. This means that all sub-flows that result from the previous sub-stream operator will be attached to the given sink.

    +----------------------------+
    | Resulting Sink             |
    |                            |
    |  +------+        +------+  |
    |  |      |        |      |  |
In ~~> | flow | ~Out~> | sink |  |
    |  |      |        |      |  |
    |  +------+        +------+  |
    +----------------------------+

Note that attributes set on the returned graph, including async boundaries are now for the entire graph and not the SubFlow. for example async will not have any effect as the returned graph is the entire, closed graph.

Transform this Flow by appending the given processing steps.

    +----------------------------+
    | Resulting Flow             |
    |                            |
    |  +------+        +------+  |
    |  |      |        |      |  |
In ~~> | this | ~Out~> | flow | ~~> T
    |  |      |        |      |  |
    |  +------+        +------+  |
    +----------------------------+

The materialized value of the combined Flow will be the materialized value of the current flow (ignoring the other Flow’s value), use viaMat if a different strategy is needed.

Attaches the given Sink to this Flow as a wire tap, meaning that elements that pass through will also be sent to the wire-tap Sink, without the latter affecting the mainline flow. If the wire-tap Sink backpressures, elements that would've been sent to it will be dropped instead.

It is similar to #alsoTo which does backpressure instead of dropping elements.

Emits when element is available and demand exists from the downstream; the element will also be sent to the wire-tap Sink if there is demand.

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

This is a simplified version of wireTap(Sink) that takes only a simple procedure. Elements will be passed into this "side channel" function, and any of its results will be ignored.

If the wire-tap operation is slow (it backpressures), elements that would've been sent to it will be dropped instead. It is similar to #alsoTo which does backpressure instead of dropping elements.

This operation is useful for inspecting the passed through element, usually by means of side-effecting operations (such as println, or emitting metrics), for each element without having to modify it.

For logging signals (elements, completion, error) consider using the log operator instead, along with appropriate ActorAttributes.logLevels.

Emits when upstream emits an element; the same element will be passed to the attached function, as well as to the downstream operator

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels

Change the attributes of this Source to the given ones and seal the list of attributes. This means that further calls will not be able to remove these attributes, but instead add new ones. Note that this operation has no effect on an empty Flow (because the attributes apply only to the contained processing operators).

Combine the elements of current Flow and the given Source into a stream of tuples.

Emits when all of the inputs has an element available

Backpressures when downstream backpressures

Completes when any upstream completes

Cancels when downstream cancels

Combine the elements of current flow and the given Source into a stream of tuples.

Emits when at first emits when both inputs emit, and then as long as any input emits (coupled to the default value of the completed input).

Backpressures when downstream backpressures

Completes when all upstream completes

Cancels when downstream cancels

Combine the elements of current Flow and the given Source into a stream of tuples, picking always the latest element of each.

Emits when all of the inputs have at least an element available, and then each time an element becomes available on either of the inputs

Backpressures when downstream backpressures

Completes when any upstream completes

Cancels when downstream cancels

Put together the elements of current Flow and the given Source into a stream of combined elements using a combiner function, picking always the latest element of each.

Emits when all of the inputs have at least an element available, and then each time an element becomes available on either of the inputs

Backpressures when downstream backpressures

Completes when any upstream completes

Cancels when downstream cancels

Put together the elements of current Flow and the given Source into a stream of combined elements using a combiner function.

Emits when all of the inputs has an element available

Backpressures when downstream backpressures

Completes when any upstream completes

Cancels when downstream cancels

Combine the elements of current Flow into a stream of tuples consisting of all elements paired with their index. Indices start at 0.

Emits when upstream emits an element and is paired with their index

Backpressures when downstream backpressures

Completes when upstream completes

Cancels when downstream cancels