82 lines
4.2 KiB
C
82 lines
4.2 KiB
C
#pragma once
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// Baselib_SystemSemaphore
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// In computer science, a semaphore is a variable or abstract data type used to control access to a common resource by multiple processes in a concurrent
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// system such as a multitasking operating system. A semaphore is simply a variable. This variable is used to solve critical section problems and to achieve
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// process synchronization in the multi processing environment. A trivial semaphore is a plain variable that is changed (for example, incremented or
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// decremented, or toggled) depending on programmer-defined conditions.
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//
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// A useful way to think of a semaphore as used in the real-world system is as a record of how many units of a particular resource are available, coupled with
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// operations to adjust that record safely (i.e. to avoid race conditions) as units are required or become free, and, if necessary, wait until a unit of the
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// resource becomes available.
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//
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// "Semaphore (programming)", Wikipedia: The Free Encyclopedia
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// https://en.wikipedia.org/w/index.php?title=Semaphore_(programming)&oldid=872408126
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#ifdef __cplusplus
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BASELIB_C_INTERFACE
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{
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#endif
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typedef struct Baselib_SystemSemaphore_Handle { void* handle; } Baselib_SystemSemaphore_Handle;
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// This is the maximum number of tokens that can be made available on a semaphore
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enum { Baselib_SystemSemaphore_MaxCount = INT32_MAX };
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// Creates a counting semaphore synchronization primitive.
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//
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// If there are not enough system resources to create a semaphore, process abort is triggered.
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//
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// \returns A handle to a semaphore instance. Use Baselib_SystemSemaphore_Free to free the semaphore.
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BASELIB_API Baselib_SystemSemaphore_Handle Baselib_SystemSemaphore_Create(void);
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// Creates a counting semaphore synchronization primitive given a memory buffer.
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//
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// Semaphore is created in-place in semaphoreData and must be atleast Baselib_SystemSemaphore_PlatformSize in size.
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// (Some platforms dont support in-place creation and this function then works the same as Baselib_SystemSemaphore_Create() )
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//
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// \returns A handle to a semaphore instance. Use Baselib_Semaphore_FreeInplace to free the semaphore.
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BASELIB_API Baselib_SystemSemaphore_Handle Baselib_SystemSemaphore_CreateInplace(void* semaphoreData);
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// Wait for semaphore token to become available
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//
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BASELIB_API void Baselib_SystemSemaphore_Acquire(Baselib_SystemSemaphore_Handle semaphore);
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// Try to consume a token and return immediately.
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//
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// \returns true if token was consumed. false if not.
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BASELIB_API bool Baselib_SystemSemaphore_TryAcquire(Baselib_SystemSemaphore_Handle semaphore);
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// Wait for semaphore token to become available
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//
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// Timeout passed to this function may be subject to system clock resolution.
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// If the system clock has a resolution of e.g. 16ms that means this function may exit with a timeout error 16ms earlier than originally scheduled.
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//
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// \param timeout Time to wait for token to become available.
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//
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// \returns true if token was consumed. false if timeout was reached.
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BASELIB_API bool Baselib_SystemSemaphore_TryTimedAcquire(Baselib_SystemSemaphore_Handle semaphore, uint32_t timeoutInMilliseconds);
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// Submit tokens to the semaphore.
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//
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// Increase the number of available tokens on the semaphore by `count`. Any waiting threads will be notified there are new tokens available.
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// If count reach `Baselib_SystemSemaphore_MaxCount` this function silently discard any overflow.
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// Note that hitting max count may inflict a heavy performance penalty.
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BASELIB_API void Baselib_SystemSemaphore_Release(Baselib_SystemSemaphore_Handle semaphore, uint32_t count);
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// Reclaim resources and memory held by the semaphore.
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//
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// If threads are waiting on the semaphore, calling free may cause process abort.
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BASELIB_API void Baselib_SystemSemaphore_Free(Baselib_SystemSemaphore_Handle semaphore);
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// Reclaim resources held by the semaphore created using Baselib_SystemSemaphore_CreateInplace
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//
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// If threads are waiting on the semaphore, calling free will trigger an assert and may cause process abort.
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// Must not be used to free a semaphore created with Baselib_Semaphore_Create
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BASELIB_API void Baselib_SystemSemaphore_FreeInplace(Baselib_SystemSemaphore_Handle semaphore);
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#ifdef __cplusplus
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} // BASELIB_C_INTERFACE
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#endif
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