Mutex

Inherits: RefCounted < Object

A binary Semaphore for synchronization of multiple Threads.

Description

A synchronization mutex (mutual exclusion). This is used to synchronize multiple Threads, and is equivalent to a binary Semaphore. It guarantees that only one thread can access a critical section at a time.

This is a reentrant mutex, meaning that it can be locked multiple times by one thread, provided it also unlocks it as many times.

Warning: Mutexes must be used carefully to avoid deadlocks.

Warning: To ensure proper cleanup without crashes or deadlocks, the following conditions must be met:

• When a Mutex‘s reference count reaches zero and it is therefore destroyed, no threads (including the one on which the destruction will happen) must have it locked.

• When a Thread‘s reference count reaches zero and it is therefore destroyed, it must not have any mutex locked.

Tutorials

• Using multiple threads

• Thread-safe APIs

Methods

Method Descriptions

void lock() 🔗

Locks this Mutex, blocks until it is unlocked by the current owner.

Note: This function returns without blocking if the thread already has ownership of the mutex.

bool try_lock() 🔗

Tries locking this Mutex, but does not block. Returns true on success, false otherwise.

Note: This function returns true if the thread already has ownership of the mutex.

void unlock() 🔗

Unlocks this Mutex, leaving it to other threads.

Note: If a thread called lock or try_lock multiple times while already having ownership of the mutex, it must also call unlock the same number of times in order to unlock it correctly.

Warning: Calling unlock more times that lock on a given thread, thus ending up trying to unlock a non-locked mutex, is wrong and may causes crashes or deadlocks.

User-contributed notes

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