godot-docs/classes/class_mutex.rst

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.. _class_Mutex:

Mutex
=====

**Inherits:** :ref:`Reference<class_Reference>` **<** :ref:`Object<class_Object>`

A synchronization mutex (mutual exclusion).

.. 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 ever acquire the lock at a time. A mutex can be used to protect a critical section; however, be careful to avoid deadlocks.

It's of the recursive kind, so it can be locked multiple times by one thread, provided it also unlocks it as many times.

\ **Warning:**\ 

To guarantee that the operating system is able to perform proper cleanup (no crashes, no deadlocks), these conditions must be met:

- By the time a **Mutex**'s reference count reaches zero and therefore it is destroyed, no threads (including the one on which the destruction will happen) must have it locked.

- By the time a :ref:`Thread<class_Thread>`'s reference count reaches zero and therefore it is destroyed, it must not have any mutex locked.

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

Tutorials
---------

- :doc:`../tutorials/performance/threads/using_multiple_threads`

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

Methods
-------

.. table::
   :widths: auto

   +---------------------------------------+----------------------------------------------------------+
   | void                                  | :ref:`lock<class_Mutex_method_lock>` **(** **)**         |
   +---------------------------------------+----------------------------------------------------------+
   | :ref:`Error<enum_@GlobalScope_Error>` | :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:`Error<enum_@GlobalScope_Error>` **try_lock** **(** **)**

Tries locking this **Mutex**, but does not block. Returns :ref:`@GlobalScope.OK<class_@GlobalScope_constant_OK>` on success, :ref:`@GlobalScope.ERR_BUSY<class_@GlobalScope_constant_ERR_BUSY>` otherwise.

\ **Note:** This function returns :ref:`@GlobalScope.OK<class_@GlobalScope_constant_OK>` 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.)`
.. |static| replace:: :abbr:`static (This method doesn't need an instance to be called, so it can be called directly using the class name.)`