virtualx-engine/doc/classes/Mutex.xml

<?xml version="1.0" encoding="UTF-8" ?>
<class name="Mutex" inherits="RefCounted" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
	<brief_description>
		A binary [Semaphore] for synchronization of multiple [Thread]s.
	</brief_description>
	<description>
		A synchronization mutex (mutual exclusion). This is used to synchronize multiple [Thread]s, 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.
		[b]Warning:[/b] Mutexes must be used carefully to avoid deadlocks.
		[b]Warning:[/b] 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.
	</description>
	<tutorials>
		<link title="Using multiple threads">$DOCS_URL/tutorials/performance/using_multiple_threads.html</link>
		<link title="Thread-safe APIs">$DOCS_URL/tutorials/performance/thread_safe_apis.html</link>
	</tutorials>
	<methods>
		<method name="lock">
			<return type="void" />
			<description>
				Locks this [Mutex], blocks until it is unlocked by the current owner.
				[b]Note:[/b] This function returns without blocking if the thread already has ownership of the mutex.
			</description>
		</method>
		<method name="try_lock">
			<return type="bool" />
			<description>
				Tries locking this [Mutex], but does not block. Returns [code]true[/code] on success, [code]false[/code] otherwise.
				[b]Note:[/b] This function returns [code]true[/code] if the thread already has ownership of the mutex.
			</description>
		</method>
		<method name="unlock">
			<return type="void" />
			<description>
				Unlocks this [Mutex], leaving it to other threads.
				[b]Note:[/b] If a thread called [method lock] or [method try_lock] multiple times while already having ownership of the mutex, it must also call [method unlock] the same number of times in order to unlock it correctly.
				[b]Warning:[/b] Calling [method unlock] more times that [method lock] on a given thread, thus ending up trying to unlock a non-locked mutex, is wrong and may causes crashes or deadlocks.
			</description>
		</method>
	</methods>
</class>