Crate async_lock

Async synchronization primitives.

This crate provides the following primitives:

• Barrier - enables tasks to synchronize all together at the same time.
• Mutex - a mutual exclusion lock.
• RwLock - a reader-writer lock, allowing any number of readers or a single writer.
• Semaphore - limits the number of concurrent operations.

Relationship with std::sync

In general, you should consider using std::sync types over types from this crate.

There are two primary use cases for types from this crate:

• You need to use a synchronization primitive in a no_std environment.
• You need to hold a lock across an .await point. (Holding an std::sync lock guard across an .await will make your future non-Send, and is also highly likely to cause deadlocks.)

If you already use libstd and you aren’t holding locks across await points (there is a Clippy lint called await_holding_lock that emits warnings for this scenario), you should consider std::sync instead of this crate. Those types are optimized for the currently running operating system, are less complex and are generally much faster.

In contrast, async-lock’s notification system uses std::sync::Mutex under the hood if the std feature is enabled, and will fall back to a significantly slower strategy if it is not. So, there are few cases where async-lock is a win for performance over std::sync.

Modules

• futures
  Named futures for use with async_lock primitives.

Structs

• Barrier
  A counter to synchronize multiple tasks at the same time.
• BarrierWaitResult
  Returned by Barrier::wait() when all tasks have called it.
• Mutex
  An async mutex.
• MutexGuard
  A guard that releases the mutex when dropped.
• MutexGuardArc
  An owned guard that releases the mutex when dropped.
• OnceCell
  A memory location that can be written to at most once.
• RwLock
  An async reader-writer lock.
• RwLockReadGuard
  A guard that releases the read lock when dropped.
• RwLockReadGuardArc
  An owned, reference-counting guard that releases the read lock when dropped.
• RwLockUpgradableReadGuard
  A guard that releases the upgradable read lock when dropped.
• RwLockUpgradableReadGuardArc
  An owned, reference-counting guard that releases the upgradable read lock when dropped.
• RwLockWriteGuard
  A guard that releases the write lock when dropped.
• RwLockWriteGuardArc
  An owned, reference-counted guard that releases the write lock when dropped.
• Semaphore
  A counter for limiting the number of concurrent operations.
• SemaphoreGuard
  A guard that releases the acquired permit.
• SemaphoreGuardArc
  An owned guard that releases the acquired permit.