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

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.

Typedef Documentation

SEM

typedef struct SEM SEM

Opaque type of a semaphore.

Function Documentation

P()

void P

(

SEM *

sem

)

P-operation.

Attempts to decrement the semaphore value by 1. If the semaphore value is not a positive number, the operation blocks until a V-operation increments the value and the P-operation succeeds.

Parameters

sem	Handle of the semaphore to decrement.

semCreate()

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.

It is legal to initialize the semaphore with a negative value. If this is the case, in order to reset the semaphore counter to zero, the V-operation must be performed (-initVal) times.

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.

V()

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.