1 stable release
1.10.2 | Feb 25, 2023 |
---|
#1172 in Concurrency
Used in rayon-wasm
260KB
4.5K
SLoC
Rayon-core represents the "core, stable" APIs of Rayon: join, scope, and so forth, as well as the ability to create custom thread-pools with ThreadPool.
Maybe worth mentioning: users are not necessarily intended to directly access rayon-core; all its APIs are mirror in the rayon crate. To that end, the examples in the docs use rayon::join and so forth rather than rayon_core::join.
rayon-core aims to never, or almost never, have a breaking change to its API, because each revision of rayon-core also houses the global thread-pool (and hence if you have two simultaneous versions of rayon-core, you have two thread-pools).
Please see Rayon Docs for details about using Rayon.
Rayon-core currently requires rustc 1.56.0
or greater.
lib.rs
:
Rayon-core houses the core stable APIs of Rayon.
These APIs have been mirrored in the Rayon crate and it is recommended to use these from there.
join
is used to take two closures and potentially run them in parallel.
- It will run in parallel if task B gets stolen before task A can finish.
- It will run sequentially if task A finishes before task B is stolen and can continue on task B.
scope
creates a scope in which you can run any number of parallel tasks.
These tasks can spawn nested tasks and scopes, but given the nature of work stealing, the order of execution can not be guaranteed.
The scope will exist until all tasks spawned within the scope have been completed.
spawn
add a task into the 'static' or 'global' scope, or a local scope created by the scope()
function.
ThreadPool
can be used to create your own thread pools (using ThreadPoolBuilder
) or to customize the global one.
Tasks spawned within the pool (using install()
, join()
, etc.) will be added to a deque,
where it becomes available for work stealing from other threads in the local threadpool.
Global fallback when threading is unsupported
Rayon uses std
APIs for threading, but some targets have incomplete implementations that
always return Unsupported
errors. The WebAssembly wasm32-unknown-unknown
and wasm32-wasi
targets are notable examples of this. Rather than panicking on the unsupported error when
creating the implicit global threadpool, Rayon configures a fallback mode instead.
This fallback mode mostly functions as if it were using a single-threaded "pool", like setting
RAYON_NUM_THREADS=1
. For example, join
will execute its two closures sequentially, since
there is no other thread to share the work. However, since the pool is not running independent
of the main thread, non-blocking calls like spawn
may not execute at all, unless a lower-
priority call like broadcast
gives them an opening. The fallback mode does not try to emulate
anything like thread preemption or async
task switching.
Explicit ThreadPoolBuilder
methods always report their error without any fallback.
Restricting multiple versions
In order to ensure proper coordination between threadpools, and especially
to make sure there's only one global threadpool, rayon-core
is actively
restricted from building multiple versions of itself into a single target.
You may see a build error like this in violation:
error: native library `rayon-core` is being linked to by more
than one package, and can only be linked to by one package
While we strive to keep rayon-core
semver-compatible, it's still
possible to arrive at this situation if different crates have overly
restrictive tilde or inequality requirements for rayon-core
. The
conflicting requirements will need to be resolved before the build will
succeed.
Dependencies
~640KB
~11K SLoC