Crate lock_api

This library provides type-safe and fully-featured Mutex and RwLock types which wrap a simple raw mutex or rwlock type. This has several benefits: not only does it eliminate a large portion of the work in implementing custom lock types, it also allows users to write code which is generic with regards to different lock implementations.

Basic usage of this crate is very straightforward:

1. Create a raw lock type. This should only contain the lock state, not any data protected by the lock.
2. Implement the RawMutex trait for your custom lock type.
3. Export your mutex as a type alias for lock_api::Mutex, and your mutex guard as a type alias for lock_api::MutexGuard. See the example below for details.

This process is similar for RwLocks, except that two guards need to be exported instead of one. (Or 3 guards if your type supports upgradable read locks, see extension traits below for details)

Example

use lock_api::{RawMutex, Mutex, GuardSend};
use std::sync::atomic::{AtomicBool, Ordering};

// 1. Define our raw lock type
pub struct RawSpinlock(AtomicBool);

// 2. Implement RawMutex for this type
unsafe impl RawMutex for RawSpinlock {
    const INIT: RawSpinlock = RawSpinlock(AtomicBool::new(false));

    // A spinlock guard can be sent to another thread and unlocked there
    type GuardMarker = GuardSend;

    fn lock(&self) {
        // Note: This isn't the best way of implementing a spinlock, but it
        // suffices for the sake of this example.
        while !self.try_lock() {}
    }

    fn try_lock(&self) -> bool {
        self.0
            .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
            .is_ok()
    }

    fn unlock(&self) {
        self.0.store(false, Ordering::Release);
    }
}

// 3. Export the wrappers. This are the types that your users will actually use.
pub type Spinlock<T> = lock_api::Mutex<RawSpinlock, T>;
pub type SpinlockGuard<'a, T> = lock_api::MutexGuard<'a, RawSpinlock, T>;

Extension traits

In addition to basic locking & unlocking functionality, you have the option of exposing additional functionality in your lock types by implementing additional traits for it. Examples of extension features include:

• Fair unlocking (RawMutexFair, RawRwLockFair)
• Lock timeouts (RawMutexTimed, RawRwLockTimed)
• Downgradable write locks (RawRwLockDowngradable)
• Recursive read locks (RawRwLockRecursive)
• Upgradable read locks (RawRwLockUpgrade)

The Mutex and RwLock wrappers will automatically expose this additional functionality if the raw lock type implements these extension traits.

Cargo features

This crate supports two cargo features:

• owning_ref: Allows your lock types to be used with the owning_ref crate.
• nightly: Enables nightly-only features. At the moment the only such feature is const fn constructors for lock types.

Structs

GuardNoSend	Marker type which indicates that the Guard type for a lock is not Send.
GuardSend	Marker type which indicates that the Guard type for a lock is Send.
MappedMutexGuard	An RAII mutex guard returned by MutexGuard::map, which can point to a subfield of the protected data.
MappedReentrantMutexGuard	An RAII mutex guard returned by ReentrantMutexGuard::map, which can point to a subfield of the protected data.
MappedRwLockReadGuard	An RAII read lock guard returned by RwLockReadGuard::map, which can point to a subfield of the protected data.
MappedRwLockWriteGuard	An RAII write lock guard returned by RwLockWriteGuard::map, which can point to a subfield of the protected data.
Mutex	A mutual exclusion primitive useful for protecting shared data
MutexGuard	An RAII implementation of a "scoped lock" of a mutex. When this structure is dropped (falls out of scope), the lock will be unlocked.
ReentrantMutex	A mutex which can be recursively locked by a single thread.
ReentrantMutexGuard	An RAII implementation of a "scoped lock" of a reentrant mutex. When this structure is dropped (falls out of scope), the lock will be unlocked.
RwLock	A reader-writer lock
RwLockReadGuard	RAII structure used to release the shared read access of a lock when dropped.
RwLockUpgradableReadGuard	RAII structure used to release the upgradable read access of a lock when dropped.
RwLockWriteGuard	RAII structure used to release the exclusive write access of a lock when dropped.

Traits

GetThreadId	Helper trait which returns a non-zero thread ID.
RawMutex	Basic operations for a mutex.
RawMutexFair	Additional methods for mutexes which support fair unlocking.
RawMutexTimed	Additional methods for mutexes which support locking with timeouts.
RawRwLock	Basic operations for a reader-writer lock.
RawRwLockDowngrade	Additional methods for RwLocks which support atomically downgrading an exclusive lock to a shared lock.
RawRwLockFair	Additional methods for RwLocks which support fair unlocking.
RawRwLockRecursive	Additional methods for RwLocks which support recursive read locks.
RawRwLockRecursiveTimed	Additional methods for RwLocks which support recursive read locks and timeouts.
RawRwLockTimed	Additional methods for RwLocks which support locking with timeouts.
RawRwLockUpgrade	Additional methods for RwLocks which support atomically upgrading a shared lock to an exclusive lock.
RawRwLockUpgradeDowngrade	Additional methods for RwLocks which support upgradable locks and lock downgrading.
RawRwLockUpgradeFair	Additional methods for RwLocks which support upgradable locks and fair unlocking.
RawRwLockUpgradeTimed	Additional methods for RwLocks which support upgradable locks and locking with timeouts.