ualarm - schedule signal after given number of microseconds
#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 since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
-
Before glibc 2.12:
-
_BSD_SOURCE || _XOPEN_SOURCE >= 500
The
ualarm() function causes the signal
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 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.
This function returns the number of microseconds remaining for any alarm that
was previously set, or 0 if no alarm was pending.
- 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.)
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| ualarm () |
Thread safety |
MT-Safe |
4.3BSD, POSIX.1-2001. POSIX.1-2001 marks
ualarm() as obsolete.
POSIX.1-2008 removes the specification of
ualarm(). 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 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_settime(2),
usleep(3) is
unspecified.
This function is obsolete. Use
setitimer(2) or POSIX interval timers
(
timer_create(2), etc.) instead.
alarm(2),
getitimer(2),
nanosleep(2),
select(2),
setitimer(2),
usleep(3),
time(7)