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Execution control library (since C++26)

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Execution control library
 

The Execution control library provides a framework for managing asynchronous execution on generic execution resources.

The library aims to provide vocabulary types for asynchronous operations and to allow the construction of task execution graphs in a simple, composable way.

Contents

[edit] Library-wide definitions

  • Sender: A description of asynchronous work to be sent for execution. Produces an operation state (below).
  • Senders asynchronously “send” their results to listeners called “receivers” (below).
  • Senders can be composed into task graphs using generic algorithms.
  • Sender factories and adaptors are generic algorithms that capture common async patterns in objects satisfying the sender concept.
  • Receiver: A generalized callback that consumes or “receives” the asynchronous results produced by a sender.
  • Receivers have three different “channels” through which a sender may propagate results: success, failure, and canceled, so-named “value”, “error”, and “stopped”.
  • Receivers provide an extensible execution environment: a set of key/value pairs that the consumer can use to parameterize the asynchronous operation.
  • Operation State: An object that contains the state needed by the asynchronous operation.
  • A sender and receiver are connected when passed to the std::execution::connect function.
  • The result of connecting a sender and a receiver is an operation state.
  • Work is not enqueued for execution until “start” is called on an operation state.
  • Once started, the operation state’s lifetime cannot end before the async operation is complete, and its address must be stable.
  • Scheduler: A lightweight handle to an execution context.
  • An execution context is a source of asynchronous execution such as a thread pool or a GPU stream.
  • A scheduler is a factory for a sender that completes its receiver from a thread of execution owned by the execution context.

[edit] Library utilities

[edit] Concepts

[edit] Schedulers

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 specifies that a type is a scheduler
(concept) [edit]

[edit] Senders

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 specifies that a type is a sender
(concept) [edit]
(C++26)
 specifies a sender that can create asynchronous operations for given associated environment type
(concept) [edit]
(C++26)
 specifies a sender that can connect with a specific receiver type
(concept) [edit]

[edit] Receivers

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 specifies that a type is a receiver
(concept) [edit]
(C++26)
 specifies that a type is a receiver for given completion signatures
(concept) [edit]

[edit] Operation states

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 specifies that a type is an operation state
(concept) [edit]

[edit] Utility components

[edit] Execution contexts

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 execution resource holding a thread-safe MPSC task queue and a manually-driven event loop
(class) [edit]

[edit] Execution domains

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 default execution domain tag type that dispatches transformations from a sender tag
(class) [edit]
(C++26)
 transforms into a new sender under a given execution domain tag
(function template) [edit]
(C++26)
 transforms into a new queryable object under a given execution domain tag
(function template) [edit]
(C++26)
 consumes a sender using a given sender consumer tag with a set of arguments and returns its result under a given execution domain tag
(function template) [edit]

[edit] Forward progress guarantee

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 specifies a forward progress guarantee of execution agents created by the scheduler's associated execution resource
(enum) [edit]

[edit] Environments

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 builds a queryable object from a query object and a value
(class template) [edit]
(C++26)
 aggregates several queryable objects into one queryable object
(class template) [edit]
(C++26)
 returns the associated queryable object for its given argument
(customization point object)[edit]

[edit] Queries

Defined in header <execution>
(C++26)
 asks a query object whether it should be forwarded through queryable adaptors
(customization point object)[edit]
(C++26)
 asks a queryable object for its associated allocator
(customization point object)[edit]
(C++26)
 asks a queryable object for its associated stop token
(customization point object)[edit]
(C++26)
 asks a queryable object for its associated execution domain tag
(customization point object)[edit]
(C++26)
 asks a queryable object for its associated scheduler
(customization point object)[edit]
(C++26)
 asks a queryable object for a scheduler that can be used to delegate work to for the purpose of forward progress delegation
(customization point object)[edit]
(C++26)
 obtains the completion scheduler associated with a completion tag from a sender's attributes
(customization point object)[edit]
(C++26)
 asks a scheduler about its execution::forward_progress_guarantee
(customization point object)[edit]

[edit] Completion signatures

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 type that encodes a set of completion signatures
(class template) [edit]
(C++26)
 obtains the completion signatures of a sender
(customization point object)[edit]
(C++26)
 transforms one set of completion signatures into another
(alias template)[edit]
(C++26)
 transforms completion signatures of a sender
(alias template)[edit]
(C++26)
 obtains the tag type of a sender
(alias template)[edit]
(C++26)
 obtains the value completion type of a sender
(alias template)[edit]
(C++26)
 obtains the error completion type of a sender
(alias template)[edit]
(C++26)
 determines whether the sender supports stopped completion
(variable template)[edit]

[edit] Coroutine utility

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 transforms an expression into awaitable object within a particular coroutine
(customization point object)[edit]
(C++26)
 when used as the base class of a coroutine promise type, enables senders to be awaitable within that coroutine type
(class template) [edit]

[edit] Core operations

[edit] Operation state

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 connects a sender with a receiver
(customization point object)[edit]
(C++26)
 starts the asynchronous operation associated with an operation_state object
(customization point object)[edit]

[edit] Completion functions

These functions are called by senders to announce the completion of the work to their receivers.

Defined in header <execution>
Defined in namespace std::execution
(C++26)
 value completion function indicating successful completion
(customization point object)[edit]
(C++26)
 error completion function indicating that an error occurred during calculation or scheduling
(customization point object)[edit]
(C++26)
 stopped completion function indicating that an operation ended before it could achieve success or failure
(customization point object)[edit]

[edit] Sender algorithms

This section is incomplete
Reason: WIP update to current standard in progress

[edit] Sender factories

A sender factory is a function that returns a sender and whose parameters have types for which the sender concept is false.

The following are sender factories:

Defined in header