Kernel sem structure

In the semid_ds structure, there exists a pointer to the base of the semaphore array itself. Each array member is of the sem structure type. It is also defined in linux/sem.h:

/* One semaphore structure for each
semaphore in the system. */
struct sem {
short   sempid; /* pid of last operation */
ushort  semval; /* current value */
ushort  semncnt;/* num procs awaiting increase in semval */
ushort  semzcnt;/* num procs awaiting semval = 0 */
};

sem_pid

The PID (process ID) that performed the last operation

sem_semval

The current value of the semaphore

sem_semncnt

Number of processes waiting for resources to become available

sem_semzcnt

Number of processes waiting for 100% resource utilization