Sends the signal SIGALRM (defined in the <signal.h> header file) to the invoking process after the number of seconds indicated by its argument has elapsed.
#include <unistd.h> unsigned int alarm (unsigned int seconds); (ISO POSIX-1) int alarm (unsigned int seconds); (Compatability)
Unless it is caught or ignored, the signal generated by alarm terminates the process. Successive alarm calls reinitialize the alarm clock. Alarms are not stacked.
Because the clock has a 1-second resolution, the signal may occur up to 1 second early. If the SIGALRM signal is caught, resumption of execution may be held up due to scheduling delays.
When the SIGALRM signal is generated, a call to SYS$WAKE is generated whether or not the process is hibernating. The pending wake causes the current pause() to return immediately (after completing any function that catches the SIGALRM).
| n | The number of seconds remaining from a previous alarm request. |