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Copyright 1989 AT&T.
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#include <unistd.h> unsigned int alarm(unsigned int seconds);
The alarm() function causes the system to generate a SIGALRM signal for the process after the number of real-time seconds specified by seconds have elapsed (see signal.h(3HEAD)). Processor scheduling delays may prevent the process from handling the signal as soon as it is generated.
If seconds is 0, a pending alarm request, if any, is cancelled. If seconds is greater than LONG_MAX/hz, seconds is rounded down to LONG_MAX/hz. The value of hz is normally 100.
Alarm requests are not stacked; only one SIGALRM generation can be scheduled in this manner; if the SIGALRM signal has not yet been generated, the call will result in rescheduling the time at which the SIGALRM signal will be generated.
The fork(2) function clears pending alarms in the child process. A new process image created by one of the exec(2) functions inherits the time left to an alarm signal in the old process's image.
If there is a previous alarm request with time remaining, alarm() returns a non-zero value that is the number of seconds until the previous request would have generated a SIGALRM signal. Otherwise, alarm() returns 0.
The alarm() function is always successful; no return value is reserved to indicate an error.
See attributes(7) for descriptions of the following attributes:
| ATTRIBUTE TYPE ATTRIBUTE VALUE |
| Interface Stability Standard |
| MT-Level Async-Signal-Safe |
exec (2), fork (2), signal.h (3HEAD), attributes (7), standards (7)