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Message Passing Protocol

Communication between components

The Message Passing Protocol defines the communication between components in Distributed Async Await.

The Message-Passing Protocol MUST support a wide array of transport mechanisms such as push or poll over http or message queues. Therefore, the specification defines the behavior of sending and receiving messages between processes with minimal requirements and minimal guarantees.

Messaging​

Every component may issue a Send(address, message) command that will result in emitting a Send(address, message) event.

command Send<T>(address : Address, message : T)

The Send command is the foundation of Distributed Async Await’s failover mechanics: Send’s AnyCast semantics enables both routing as well as transparent rerouting in case of failure. This ensures that distributed executions can adapt dynamically to changes in the process topology automatically.

Invoke-Resume Example: The Canonical Interaction

The canonical interaction in Distributed Async Await involves invoking and awaiting an asynchronous function remotely (see Distributed Coordination Protocol). This interaction involves two messages:

Invoke

invoke represents the request to invoke an execution.

Resume

resume represents the request to resume an awaiting execution.

Addressing​

Processes communicate via addresses. Distributed Async Await supports two types of addresses, UniCast addresses and AnyCast addresses.

UniCast. A UniCast address denotes an individual process. AnyCast. An AnyCast address denotes a group of processes.

data Address =
  | UniCast PSpecifier
  | AnyCast GSpecifier x optional<PSpecifier>
  • PSpecifier denotes a transport-specific specifier specifying a single progress.
  • GSpecifier denotes a transport-specific specifier specifying a group of processes.

Address Resolution​

This specification does not determine how and when addresses are resolved. Specifically, this specification does not determine whether addresses are resolved on send (early binding) or on recv (late binding).