ualarm(3) Library Functions Manual ualarm(3)
NAME
ualarm - schedule signal after given number of microseconds
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <unistd.h>
useconds_t ualarm(useconds_t usecs, useconds_t interval);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
ualarm():
Since glibc 2.12:
(_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
|| /* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500
DESCRIPTION
The ualarm() function causes the signal SIGALRM to be sent to the in-
voking process after (not less than) usecs microseconds. The delay may
be lengthened slightly by any system activity or by the time spent pro-
cessing the call or by the granularity of system timers.
Unless caught or ignored, the SIGALRM signal will terminate the
process.
If the interval argument is nonzero, further SIGALRM signals will be
sent every interval microseconds after the first.
RETURN VALUE
This function returns the number of microseconds remaining for any
alarm that was previously set, or 0 if no alarm was pending.
ERRORS
EINTR Interrupted by a signal; see signal(7).
EINVAL usecs or interval is not smaller than 1000000. (On systems
where that is considered an error.)
ATTRIBUTES
For an explanation of the terms used in this section, see attrib-
utes(7).
┌───────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├───────────────────────────────────────────┼───────────────┼─────────┤
│ ualarm() │ Thread safety │ MT-Safe │
└───────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
None.
HISTORY
4.3BSD, POSIX.1-2001. POSIX.1-2001 marks it as obsolete. Removed in
POSIX.1-2008.
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 in-
tegers in the range [0,1000000]. On the original BSD implementation,
and in glibc before glibc 2.1, the arguments to ualarm() were instead
typed as unsigned int. Programs will be more portable if they never
mention useconds_t explicitly.
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_set-
time(2), usleep(3) is unspecified.
This function is obsolete. Use setitimer(2) or POSIX interval timers
(timer_create(2), etc.) instead.
SEE ALSO
alarm(2), getitimer(2), nanosleep(2), select(2), setitimer(2),
usleep(3), time(7)
Linux man-pages 6.7 2023-10-31 ualarm(3)
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