Section (3) ualarm
ualarm — schedule signal after given number of microseconds
ualarm() function causes
SIGALRM to be sent
to the invoking process after (not less than)
usecs microseconds. The delay
may be lengthened slightly by any system activity or by the
time spent processing the call or by the granularity of
Unless caught or ignored, the
SIGALRM signal will terminate the
argument is nonzero, further
SIGALRM signals will be sent every
after the first.
This function returns the number of microseconds remaining for any alarm that was previously set, or 0 if no alarm was pending.
Interrupted by a signal; see signal(7).
intervalis not smaller than 1000000. (On systems where that is considered an error.)
For an explanation of the terms used in this section, see attributes(7).
4.3BSD, POSIX.1-2001. POSIX.1-2001 marks
ualarm() as obsolete. POSIX.1-2008 removes
the specification of
4.3BSD, SUSv2, and POSIX do not define any errors.
POSIX.1-2001 does not specify what happens if the
usecs argument is 0.
On Linux (and probably most other systems), the effect is to
cancel any pending alarm.
The type useconds_t is an
unsigned integer type capable of holding integers in the
range [0,1000000]. On the original BSD implementation, and in
glibc before version 2.1, the arguments to
ualarm() were instead typed as unsigned int. Programs will be more portable if
they never mention useconds_t
The interaction of this function with other timer functions such as alarm(2), sleep(3), nanosleep(2), setitimer(2), timer_create(2), timer_delete(2), timer_getoverrun(2), timer_gettime(2), timer_settime(2), usleep(3) is unspecified.
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Copyright (c) 2003 Andries Brouwer (aebcwi.nl)
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