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 (int initVal)
	Creates a new semaphore.
int	semDestroy (SEM *sem)
	Destroys a semaphore and frees all associated resources.
void	P (SEM *sem)
	P-operation.
void	V (SEM *sem)
	V-operation.

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Detailed Description

Semaphore implementation for the synchronization of POSIX threads.

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

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Typedef Documentation

typedef struct SEM SEM

Opaque type of a semaphore.

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Function Documentation

void P

(

SEM *

sem

)

P-operation.

Attempts to decrement the semaphore value by 1. If the semaphore value is 0, the operation blocks until a V-operation increments the value and the P-operation succeeds.

Parameters:

sem

Handle of the semaphore to decrement.

SEM* semCreate

(

int

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.

int semDestroy

(

SEM *

sem

)

Destroys a semaphore and frees all associated resources.

If an error occurs, errno is set to an appropriate value.

Parameters:

sem

Handle of the semaphore to destroy. If a NULL pointer is passed, the implementation does nothing, but returns 0.

Returns:

0 on success, negative value on error. In case of an error, not all resources may have been freed, but nevertheless the semaphore handle must not be used any more.

void V

(

SEM *

sem

)

V-operation.

Increments the semaphore value by 1 and notifies P-operations that are blocked on the semaphore of the change.

Parameters:

sem

Handle of the semaphore to increment.