Initialize a Semaphore

sema_init(3T)

#include <thread.h>

int sema_init(sema_t *sp, unsigned int count, int type,
    void *arg);

Use sema_init(3T) to initialize the semaphore variable pointed to by sp by count amount. type can be one of the following (note that arg is currently ignored).

USYNC_PROCESS The semaphore can be used to synchronize threads in this process and other processes. Only one process should initialize the semaphore. arg is ignored.

USYNC_THREAD The semaphore can be used to synchronize threads in this process, only. arg is ignored.

Multiple threads must not initialize the same semaphore simultaneously. A semaphore must not be reinitialized while other threads may be using it.

Semaphores with Intraprocess Scope

#include <thread.h>

sema_t sp;
int ret;
int count;
count = 4;

/* to be used within this process only */
ret = sema_init(&sp, count, USYNC_THREAD, 0); 

Semaphores with Interprocess Scope

#include <thread.h>

sema_t sp;
int ret;
int count;
count = 4;

/* to be used among all the processes */
ret = sema_init (&sp, count, USYNC_PROCESS, 0);