Initialize an unnamed semaphore
#include <semaphore.h> int sem_init( sem_t * sem, int pshared, unsigned value );
|It's always safe, and typically faster, to assure that sem is 32-bit aligned.|
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The sem_init() function initializes the unnamed semaphore referred to by the sem argument. The initial counter value of this semaphore is specified by the value argument.
|You should allocate synchronization objects only in normal memory mappings. On certain processors (e.g. some PPC ones), atomic operations such as calls to pthread_mutex_lock() will cause a fault if the control structure is allocated in uncached memory.|
You can use the initialized semaphore in subsequent calls to sem_wait(), sem_trywait(), sem_post(), and sem_destroy(). An initialized semaphore is valid until it's destroyed by the sem_destroy() function, or until the memory where the semaphore resides is released.
If the pshared argument is nonzero, then the semaphore can be shared between processes via shared memory. Any process can then use sem with the sem_wait(), sem_trywait(), sem_post() and sem_destroy() functions.
|Don't mix named semaphore operations (sem_open() and sem_close()) with unnamed semaphore operations (sem_init() and sem_destroy()) on the same semaphore.|
POSIX 1003.1 SEM
Don't initialize the same semaphore from more than one thread. It's best to set up semaphores before starting any threads.
errno, sem_destroy(), sem_post(), sem_trywait(), sem_wait()