Crate futures_executor

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Built-in executors and related tools.

All asynchronous computation occurs within an executor, which is capable of spawning futures as tasks. This module provides several built-in executors, as well as tools for building your own.

All items are only available when the std feature of this library is activated, and it is activated by default.

Using a thread pool (M:N task scheduling)

Most of the time tasks should be executed on a thread pool. A small set of worker threads can handle a very large set of spawned tasks (which are much lighter weight than threads). Tasks spawned onto the pool with the spawn_ok function will run ambiently on the created threads.

Spawning additional tasks

Tasks can be spawned onto a spawner by calling its spawn_obj method directly. In the case of !Send futures, spawn_local_obj can be used instead.

Single-threaded execution

In addition to thread pools, it’s possible to run a task (and the tasks it spawns) entirely within a single thread via the LocalPool executor. Aside from cutting down on synchronization costs, this executor also makes it possible to spawn non-Send tasks, via spawn_local_obj. The LocalPool is best suited for running I/O-bound tasks that do relatively little work between I/O operations.

There is also a convenience function block_on for simply running a future to completion on the current thread.


  • An iterator which blocks on values from a stream until they become available.
  • Represents an executor context.
  • An error returned by enter if an execution scope has already been entered.
  • A single-threaded task pool for polling futures to completion.
  • A handle to a LocalPool that implements Spawn.


  • Run a future to completion on the current thread.
  • Turn a stream into a blocking iterator.
  • Marks the current thread as being within the dynamic extent of an executor.