A C function that allows the program to request a shared or exclusive lock on a file. Returns 0 on sucess and -1 on failure.
#define LOCK_SH 1 /* shared lock */
#define LOCK_EX 2 /* exclusive lock */
#define LOCK_NB 4 /* don't block when locking */
#define LOCK_UN 8 /* unlock */
int operation );
(from the flock() man page)
Where filedes is a file descriptor returned by open() or fcntl() and operation is one of the constants defined in the above block.