godot-docs/classes/class_mutex.rst

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.. _class_Mutex:

Mutex
=====

**Inherits:** :ref:`RefCounted<class_RefCounted>` **<** :ref:`Object<class_Object>`

A binary :ref:`Semaphore<class_Semaphore>` for synchronization of multiple :ref:`Thread<class_Thread>`\ s.

.. rst-class:: classref-introduction-group

Description
-----------

A synchronization mutex (mutual exclusion). This is used to synchronize multiple :ref:`Thread<class_Thread>`\ s, and is equivalent to a binary :ref:`Semaphore<class_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 :ref:`Thread<class_Thread>`'s reference count reaches zero and it is therefore destroyed, it must not have any mutex locked.

.. rst-class:: classref-introduction-group

Tutorials
---------

- :doc:`Using multiple threads <../tutorials/performance/using_multiple_threads>`

- :doc:`Thread-safe APIs <../tutorials/performance/thread_safe_apis>`

.. rst-class:: classref-reftable-group

Methods
-------

.. table::
   :widths: auto

   +-------------------------+----------------------------------------------------------+
   | void                    | :ref:`lock<class_Mutex_method_lock>` **(** **)**         |
   +-------------------------+----------------------------------------------------------+
   | :ref:`bool<class_bool>` | :ref:`try_lock<class_Mutex_method_try_lock>` **(** **)** |
   +-------------------------+----------------------------------------------------------+
   | void                    | :ref:`unlock<class_Mutex_method_unlock>` **(** **)**     |
   +-------------------------+----------------------------------------------------------+

.. rst-class:: classref-section-separator

----

.. rst-class:: classref-descriptions-group

Method Descriptions
-------------------

.. _class_Mutex_method_lock:

.. rst-class:: classref-method

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.

.. rst-class:: classref-item-separator

----

.. _class_Mutex_method_try_lock:

.. rst-class:: classref-method

:ref:`bool<class_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.

.. rst-class:: classref-item-separator

----

.. _class_Mutex_method_unlock:

.. rst-class:: classref-method

void **unlock** **(** **)**

Unlocks this **Mutex**, leaving it to other threads.

\ **Note:** If a thread called :ref:`lock<class_Mutex_method_lock>` or :ref:`try_lock<class_Mutex_method_try_lock>` multiple times while already having ownership of the mutex, it must also call :ref:`unlock<class_Mutex_method_unlock>` the same number of times in order to unlock it correctly.

\ **Warning:** Calling :ref:`unlock<class_Mutex_method_unlock>` more times that :ref:`lock<class_Mutex_method_lock>` on a given thread, thus ending up trying to unlock a non-locked mutex, is wrong and may causes crashes or deadlocks.

.. |virtual| replace:: :abbr:`virtual (This method should typically be overridden by the user to have any effect.)`
.. |const| replace:: :abbr:`const (This method has no side effects. It doesn't modify any of the instance's member variables.)`
.. |vararg| replace:: :abbr:`vararg (This method accepts any number of arguments after the ones described here.)`
.. |constructor| replace:: :abbr:`constructor (This method is used to construct a type.)`
.. |static| replace:: :abbr:`static (This method doesn't need an instance to be called, so it can be called directly using the class name.)`
.. |operator| replace:: :abbr:`operator (This method describes a valid operator to use with this type as left-hand operand.)`
.. |bitfield| replace:: :abbr:`BitField (This value is an integer composed as a bitmask of the following flags.)`