godot-docs/classes/class_semaphore.rst

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.. _class_Semaphore:

Semaphore
=========

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

A synchronization semaphore.

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

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

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

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

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

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

Tutorials
---------

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

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

Methods
-------

.. table::
   :widths: auto

   +---------------------------------------+--------------------------------------------------------------+
   | :ref:`Error<enum_@GlobalScope_Error>` | :ref:`post<class_Semaphore_method_post>` **(** **)**         |
   +---------------------------------------+--------------------------------------------------------------+
   | :ref:`Error<enum_@GlobalScope_Error>` | :ref:`try_wait<class_Semaphore_method_try_wait>` **(** **)** |
   +---------------------------------------+--------------------------------------------------------------+
   | :ref:`Error<enum_@GlobalScope_Error>` | :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

:ref:`Error<enum_@GlobalScope_Error>` **post** **(** **)**

Lowers the **Semaphore**, allowing one more thread in.

\ **Note:** This method internals' can't possibly fail, but an error code is returned for backwards compatibility, which will always be :ref:`@GlobalScope.OK<class_@GlobalScope_constant_OK>`.

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

----

.. _class_Semaphore_method_try_wait:

.. rst-class:: classref-method

:ref:`Error<enum_@GlobalScope_Error>` **try_wait** **(** **)**

Like :ref:`wait<class_Semaphore_method_wait>`, but won't block, so if the value is zero, fails immediately and returns :ref:`@GlobalScope.ERR_BUSY<class_@GlobalScope_constant_ERR_BUSY>`. If non-zero, it returns :ref:`@GlobalScope.OK<class_@GlobalScope_constant_OK>` to report success.

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

----

.. _class_Semaphore_method_wait:

.. rst-class:: classref-method

:ref:`Error<enum_@GlobalScope_Error>` **wait** **(** **)**

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

\ **Note:** This method internals' can't possibly fail, but an error code is returned for backwards compatibility, which will always be :ref:`@GlobalScope.OK<class_@GlobalScope_constant_OK>`.

.. |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.)`