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ualarm(3)
UALARM(3) Linux Programmer's Manual UALARM(3)
NAME
ualarm - schedule signal after given number of microseconds
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 since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 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
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.
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
attributes(7).
allbox; lb lb lb l l l. Interface Attribute Value T{ ualarm()
T} Thread safety MT-Safe
CONFORMING TO
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.
NOTES
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_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This function is obsolete.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)
COLOPHON
This page is part of release 5.02 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
2017-09-15 UALARM(3)