ualarm - schedule signal after given number of microseconds
useconds_t ualarm(useconds_t usecs, useconds_t interval);
Feature Test Macro Requirements for glibc (see feature_test_macros
- 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
() 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
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.
- Interrupted by a signal; see signal(7).
- 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
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
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
The interaction of this function with other timer functions such as
This function is obsolete. Use setitimer
(2) or POSIX interval timers
(2), etc.) instead.