Crate rayon

Rayon is a data-parallelism library that makes it easy to convert sequential computations into parallel.

It is lightweight and convenient for introducing parallelism into existing code. It guarantees data-race free executions and takes advantage of parallelism when sensible, based on work-load at runtime.

How to use Rayon

There are two ways to use Rayon:

• High-level parallel constructs are the simplest way to use Rayon and also typically the most efficient.
  • Parallel iterators make it easy to convert a sequential iterator to execute in parallel.
    • The ParallelIterator trait defines general methods for all parallel iterators.
    • The IndexedParallelIterator trait adds methods for iterators that support random access.
  • The par_sort method sorts &mut [T] slices (or vectors) in parallel.
  • par_extend can be used to efficiently grow collections with items produced by a parallel iterator.
• Custom tasks let you divide your work into parallel tasks yourself.
  • join is used to subdivide a task into two pieces.
  • scope creates a scope within which you can create any number of parallel tasks.
  • ThreadPoolBuilder can be used to create your own thread pools or customize the global one.

Basic usage and the Rayon prelude

First, you will need to add rayon to your Cargo.toml.

Next, to use parallel iterators or the other high-level methods, you need to import several traits. Those traits are bundled into the module rayon::prelude. It is recommended that you import all of these traits at once by adding use rayon::prelude::* at the top of each module that uses Rayon methods.

These traits give you access to the par_iter method which provides parallel implementations of many iterative functions such as map, for_each, filter, fold, and more.

Crate Layout

Rayon extends many of the types found in the standard library with parallel iterator implementations. The modules in the rayon crate mirror std itself: so, e.g., the option module in Rayon contains parallel iterators for the Option type, which is found in the option module of std. Similarly, the collections module in Rayon offers parallel iterator types for the collections from std. You will rarely need to access these submodules unless you need to name iterator types explicitly.

Targets without threading

Rayon has limited support for targets without std threading implementations. See the rayon_core documentation for more information about its global fallback.

Other questions?

See the Rayon FAQ.

Modules

• array
  Parallel iterator types for arrays ([T; N])
• collections
  Parallel iterator types for standard collections
• iter
  Traits for writing parallel programs using an iterator-style interface
• option
  Parallel iterator types for options
• prelude
  The rayon prelude imports the various ParallelIterator traits. The intention is that one can include use rayon::prelude::* and have easy access to the various traits and methods you will need.
• range
  Parallel iterator types for ranges, the type for values created by a..b expressions
• range_inclusive
  Parallel iterator types for inclusive ranges, the type for values created by a..=b expressions
• result
  Parallel iterator types for results
• slice
  Parallel iterator types for slices
• str
  Parallel iterator types for strings
• string
  This module contains the parallel iterator types for owned strings (String). You will rarely need to interact with it directly unless you have need to name one of the iterator types.
• vec
  Parallel iterator types for vectors (Vec<T>)

Structs

• BroadcastContext
  Provides context to a closure called by broadcast.
• FnContext
  Provides the calling context to a closure called by join_context.
• Scope
  Represents a fork-join scope which can be used to spawn any number of tasks. See scope() for more information.
• ScopeFifo
  Represents a fork-join scope which can be used to spawn any number of tasks. Those spawned from the same thread are prioritized in relative FIFO order. See scope_fifo() for more information.
• ThreadBuilder
  Thread builder used for customization via ThreadPoolBuilder::spawn_handler.
• ThreadPool
  Represents a user created thread-pool.
• ThreadPoolBuildError
  Error when initializing a thread pool.
• ThreadPoolBuilder
  Used to create a new ThreadPool or to configure the global rayon thread pool.

Enums

• Yield
  Result of yield_now() or yield_local().

Functions

• broadcast
  Executes op within every thread in the current threadpool. If this is called from a non-Rayon thread, it will execute in the global threadpool. Any attempts to use join, scope, or parallel iterators will then operate within that threadpool. When the call has completed on each thread, returns a vector containing all of their return values.
• current_num_threads
  Returns the number of threads in the current registry. If this code is executing within a Rayon thread-pool, then this will be the number of threads for the thread-pool of the current thread. Otherwise, it will be the number of threads for the global thread-pool.
• current_thread_index
  If called from a Rayon worker thread, returns the index of that thread within its current pool; if not called from a Rayon thread, returns None.
• in_place_scope
  Creates a “fork-join” scope s and invokes the closure with a reference to s. This closure can then spawn asynchronous tasks into s. Those tasks may run asynchronously with respect to the closure; they may themselves spawn additional tasks into s. When the closure returns, it will block until all tasks that have been spawned into s complete.
• in_place_scope_fifo
  Creates a “fork-join” scope s with FIFO order, and invokes the closure with a reference to s. This closure can then spawn asynchronous tasks into s. Those tasks may run asynchronously with respect to the closure; they may themselves spawn additional tasks into s. When the closure returns, it will block until all tasks that have been spawned into s complete.
• join
  Takes two closures and potentially runs them in parallel. It returns a pair of the results from those closures.
• join_context
  Identical to join, except that the closures have a parameter that provides context for the way the closure has been called, especially indicating whether they’re executing on a different thread than where join_context was called. This will occur if the second job is stolen by a different thread, or if join_context was called from outside the thread pool to begin with.
• max_num_threads
  Returns the maximum number of threads that Rayon supports in a single thread-pool.
• scope
  Creates a “fork-join” scope s and invokes the closure with a reference to s. This closure can then spawn asynchronous tasks into s. Those tasks may run asynchronously with respect to the closure; they may themselves spawn additional tasks into s. When the closure returns, it will block until all tasks that have been spawned into s complete.
• scope_fifo
  Creates a “fork-join” scope s with FIFO order, and invokes the closure with a reference to s. This closure can then spawn asynchronous tasks into s. Those tasks may run asynchronously with respect to the closure; they may themselves spawn additional tasks into s. When the closure returns, it will block until all tasks that have been spawned into s complete.
• spawn
  Puts the task into the Rayon threadpool’s job queue in the “static” or “global” scope. Just like a standard thread, this task is not tied to the current stack frame, and hence it cannot hold any references other than those with 'static lifetime. If you want to spawn a task that references stack data, use the scope() function to create a scope.
• spawn_broadcast
  Spawns an asynchronous task on every thread in this thread-pool. This task will run in the implicit, global scope, which means that it may outlast the current stack frame – therefore, it cannot capture any references onto the stack (you will likely need a move closure).
• spawn_fifo
  Fires off a task into the Rayon threadpool in the “static” or “global” scope. Just like a standard thread, this task is not tied to the current stack frame, and hence it cannot hold any references other than those with 'static lifetime. If you want to spawn a task that references stack data, use the scope_fifo() function to create a scope.
• yield_local
  Cooperatively yields execution to local Rayon work.
• yield_now
  Cooperatively yields execution to Rayon.