Semaphore APIs

 #include <sys/types.h>     #include <sys/ipc.h>     #include <sys/sem.h>     int  semget  ( key_t key, int nsems, int semflg );     int  semop  ( int semid, struct sembuf *sops, unsigned int nsops );     int  semctl  ( int semid, int semnum, int cmd, ... );