sem.h File Reference

Semaphore implementation for the synchronization of POSIX threads. More...

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Typedefs
typedef struct SEM	SEM

Functions
SEM *	semCreate (unsigned initVal)
	Creates a new semaphore.
void	semDestroy (SEM *sem)
	Destroys a semaphore and frees all associated resources.
void	down (SEM *sem)
	Acquire the semaphore.
void	up (SEM *sem)
	Release the semaphore.

Detailed Description

Semaphore implementation for the synchronization of POSIX threads.

This module implements counting semaphores suitable for the synchronization of POSIX threads. POSIX mutexes and condition variables are utilized to implement the semaphor operations.

Typedef Documentation

SEM

typedef struct SEM SEM

Opaque type of a semaphore.

Function Documentation

down()

void down

(

SEM *

sem

)

Acquire the semaphore.

Attempts to decrement the semaphore value by 1. If the semaphore value is 0, the operation blocks until a up() call increments the value.

Parameters

sem	Handle of the semaphore to decrement.

semCreate()

SEM * semCreate

(

unsigned

initVal

)

Creates a new semaphore.

This function creates a new semaphore. If an error occurs during the initialization, the implementation frees all resources already allocated by then and sets errno to an appropriate value.

Parameters

initVal

The initial value of the semaphore.

Returns

Handle for the created semaphore, or NULL if an error occurred.

semDestroy()

void semDestroy

(

SEM *

sem

)

Destroys a semaphore and frees all associated resources.

Parameters

sem	Handle of the semaphore to destroy. If a NULL pointer is passed, the implementation does nothing.

up()

void up

(

SEM *

sem

)

Release the semaphore.

Increments the semaphore value by 1 and notifies threads that are blocked on the semaphore of the change.

Parameters

sem	Handle of the semaphore to increment.