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.. DO NOT EDIT THIS FILE!!!
.. Generated automatically from Godot engine sources.
.. Generator: https://github.com/godotengine/godot/tree/master/doc/tools/make_rst.py.
.. XML source: https://github.com/godotengine/godot/tree/master/doc/classes/Semaphore.xml.

.. _class_Semaphore:

Semaphore
=========

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

A synchronization mechanism used to control access to a shared resource by :ref:`Thread<class_Thread>`\ s.

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

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

A synchronization semaphore that can be used to synchronize multiple :ref:`Thread<class_Thread>`\ s. Initialized to zero on creation. For a binary version, see :ref:`Mutex<class_Mutex>`.

\ **Warning:** Semaphores must be used carefully to avoid deadlocks.

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

- When a **Semaphore**'s reference count reaches zero and it is therefore destroyed, no threads must be waiting on it.

- When a :ref:`Thread<class_Thread>`'s reference count reaches zero and it is therefore destroyed, it must not be waiting on any semaphore.

.. 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:`post<class_Semaphore_method_post>`\ (\ count\: :ref:`int<class_int>` = 1\ ) |
   +-------------------------+-----------------------------------------------------------------------------------+
   | :ref:`bool<class_bool>` | :ref:`try_wait<class_Semaphore_method_try_wait>`\ (\ )                            |
   +-------------------------+-----------------------------------------------------------------------------------+
   | |void|                  | :ref:`wait<class_Semaphore_method_wait>`\ (\ )                                    |
   +-------------------------+-----------------------------------------------------------------------------------+

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

----

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

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

.. _class_Semaphore_method_post:

.. rst-class:: classref-method

|void| **post**\ (\ count\: :ref:`int<class_int>` = 1\ ) :ref:`🔗<class_Semaphore_method_post>`

Lowers the **Semaphore**, allowing one thread in, or more if ``count`` is specified.

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

----

.. _class_Semaphore_method_try_wait:

.. rst-class:: classref-method

:ref:`bool<class_bool>` **try_wait**\ (\ ) :ref:`🔗<class_Semaphore_method_try_wait>`

Like :ref:`wait<class_Semaphore_method_wait>`, but won't block, so if the value is zero, fails immediately and returns ``false``. If non-zero, it returns ``true`` to report success.

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

----

.. _class_Semaphore_method_wait:

.. rst-class:: classref-method

|void| **wait**\ (\ ) :ref:`🔗<class_Semaphore_method_wait>`

Waits for the **Semaphore**, if its value is zero, blocks until non-zero.

.. |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.)`
.. |void| replace:: :abbr:`void (No return value.)`