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alarm(3) Library Functions Manual alarm(3) NAME alarm, ualarm - Sets or changes the timeout of interval timers. LIBRARY Standard C Library (libc.so, libc.a) SYNOPSIS #include <unistd.h> unsigned int alarm( unsigned int seconds); useconds_t ualarm( useconds_t useconds, useconds_t interval); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: alarm(): XPG4, XPG4-UNIX ualarm(): XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS Specifies a number of real-time seconds. Specifies a number of real- time microseconds. Specifies the interval for repeating the timer. DESCRIPTION The alarm() function is used to obtain notification of a timeout after the number of real-time seconds specified by the seconds parameter has elapsed. At some time after seconds seconds have elapsed, a signal is delivered to the process. Each call resets the timer to the new value. A value of 0 (zero) disables the timer. When the notification signal is caught or ignored, no action takes place; otherwise the calling process is terminated. The alarm() function uses the ITIMER_REAL in- terval timer. The ualarm() function is used to obtain notification of a timeout after the number of real-time microseconds specified by the useconds parame- ter has elapsed. When the interval parameter is nonzero, timeout noti- fication occurs after the number of microseconds specified by the in- terval parameter has been added to the useconds parameter. When the notification signal is caught or ignored, no action takes place; other- wise the calling process is terminated. The ualarm() function is the simplified interface to the setitimer() function, and uses the ITIMER_REAL interval timer. NOTES The alarm() and ualarm() functions are supported for multithreaded ap- plications. Although the alarm() and ualarm() functions are reentrant, it should be noted that just as the second of two calls from a single thread to alarm() resets the timer, this is also true if two calls are made from different threads. RETURN VALUES If there is a previous alarm() request with time remaining, the alarm() function 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 (zero). The ualarm() function returns the number of microseconds remaining from the previous ualarm() call. If no timeouts are pending or if ualarm() has not previously been called, ualarm() returns 0 (zero). ERRORS The alarm() function sets errno to the specified values for the follow- ing conditions: [Digital] The seconds parameter specifies a value greater than 100,000,000. RELATED INFORMATION Functions: gettimer(3) Standards: standards(5) delim off alarm(3)