The architecture of Akka Streams internally consists of several distinct layers:
The architecture of Akka Streams internally consists of several distinct layers:
* The DSLs like akka.stream.scaladsl.Flow, akka.stream.scaladsl.Source etc. are the user facing API for composing streams. These DSLs are a thin wrappers around the internal akka.stream.impl.TraversalBuilder builder classes. There are Java alternatives of these DSLs in javadsl which basically wrap their scala counterpart, delegating method calls. * The akka.stream.stage.GraphStage API is the user facing API for creating new stream operators. These classes are used by the akka.stream.impl.fusing.GraphInterpreter which executes islands (subgraphs) of these operators * The high level DSLs use the akka.stream.impl.TraversalBuilder classes to build instances of akka.stream.impl.Traversal which are the representation of a materializable stream description. These builders are immutable and safely shareable. Unlike the top-level DSLs, these are classic, i.e. elements are treated as Any. * The akka.stream.impl.Traversal is the immutable, efficient representation of a stream processing graph that can be materialized. The builders exists solely for the purpose of producing a traversal in the end. * The akka.stream.impl.PhasedFusingActorMaterializer is the class that is responsible for traversing and interpreting a akka.stream.impl.Traversal. It delegates the actual task of creating executable entities and Publishers/Producers to akka.stream.impl.PhaseIslands which are plugins that understand atomic operators in the graph and able to turn them into executable entities. * The akka.stream.impl.fusing.GraphInterpreter and its actor backed wrapper