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<?xml version="1.0" encoding="UTF-8" ?>
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<class name= "Semaphore" inherits= "RefCounted" version= "4.2" xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation= "../class.xsd" >
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<brief_description >
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A synchronization mechanism used to control access to a shared resource by [Thread]s.
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</brief_description>
<description >
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A synchronization semaphore that can be used to synchronize multiple [Thread]s. Initialized to zero on creation. For a binary version, see [Mutex].
[b]Warning:[/b] Semaphores must be used carefully to avoid deadlocks.
[b]Warning:[/b] 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 [Thread]'s reference count reaches zero and it is therefore destroyed, it must not be waiting on any semaphore.
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</description>
<tutorials >
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<link title= "Using multiple threads" > $DOCS_URL/tutorials/performance/using_multiple_threads.html</link>
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<link title= "Thread-safe APIs" > $DOCS_URL/tutorials/performance/thread_safe_apis.html</link>
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</tutorials>
<methods >
<method name= "post" >
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<return type= "void" />
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<description >
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Lowers the [Semaphore], allowing one more thread in.
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</description>
</method>
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<method name= "try_wait" >
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<return type= "bool" />
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<description >
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Like [method wait], but won't block, so if the value is zero, fails immediately and returns [code]false[/code]. If non-zero, it returns [code]true[/code] to report success.
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</description>
</method>
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<method name= "wait" >
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<return type= "void" />
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<description >
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Waits for the [Semaphore], if its value is zero, blocks until non-zero.
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</description>
</method>
</methods>
</class>