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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-24 04:52:22 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-24 04:52:22 +0000
commit3d08cd331c1adcf0d917392f7e527b3f00511748 (patch)
tree312f0d1e1632f48862f044b8bb87e602dcffb5f9 /man2/timer_create.2
parentAdding debian version 6.7-2. (diff)
downloadmanpages-3d08cd331c1adcf0d917392f7e527b3f00511748.tar.xz
manpages-3d08cd331c1adcf0d917392f7e527b3f00511748.zip
Merging upstream version 6.8.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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-.\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
-.\" <mtk.manpages@gmail.com>
-.\"
-.\" SPDX-License-Identifier: Linux-man-pages-copyleft
-.\"
-.TH timer_create 2 2023-11-11 "Linux man-pages 6.7"
-.SH NAME
-timer_create \- create a POSIX per-process timer
-.SH LIBRARY
-Real-time library
-.RI ( librt ", " \-lrt )
-.SH SYNOPSIS
-.nf
-.BR "#include <signal.h>" " /* Definition of " SIGEV_* " constants */"
-.B #include <time.h>
-.P
-.BI "int timer_create(clockid_t " clockid ,
-.BI " struct sigevent *_Nullable restrict " sevp ,
-.BI " timer_t *restrict " timerid );
-.fi
-.P
-.RS -4
-Feature Test Macro Requirements for glibc (see
-.BR feature_test_macros (7)):
-.RE
-.P
-.BR timer_create ():
-.nf
- _POSIX_C_SOURCE >= 199309L
-.fi
-.SH DESCRIPTION
-.BR timer_create ()
-creates a new per-process interval timer.
-The ID of the new timer is returned in the buffer pointed to by
-.IR timerid ,
-which must be a non-null pointer.
-This ID is unique within the process, until the timer is deleted.
-The new timer is initially disarmed.
-.P
-The
-.I clockid
-argument specifies the clock that the new timer uses to measure time.
-It can be specified as one of the following values:
-.TP
-.B CLOCK_REALTIME
-A settable system-wide real-time clock.
-.TP
-.B CLOCK_MONOTONIC
-A nonsettable monotonically increasing clock that measures time
-from some unspecified point in the past that does not change
-after system startup.
-.\" Note: the CLOCK_MONOTONIC_RAW clock added for clock_gettime()
-.\" in Linux 2.6.28 is not supported for POSIX timers -- mtk, Feb 2009
-.TP
-.BR CLOCK_PROCESS_CPUTIME_ID " (since Linux 2.6.12)"
-A clock that measures (user and system) CPU time consumed by
-(all of the threads in) the calling process.
-.TP
-.BR CLOCK_THREAD_CPUTIME_ID " (since Linux 2.6.12)"
-A clock that measures (user and system) CPU time consumed by
-the calling thread.
-.\" The CLOCK_MONOTONIC_RAW that was added in Linux 2.6.28 can't be used
-.\" to create a timer -- mtk, Feb 2009
-.TP
-.BR CLOCK_BOOTTIME " (Since Linux 2.6.39)"
-.\" commit 70a08cca1227dc31c784ec930099a4417a06e7d0
-Like
-.BR CLOCK_MONOTONIC ,
-this is a monotonically increasing clock.
-However, whereas the
-.B CLOCK_MONOTONIC
-clock does not measure the time while a system is suspended, the
-.B CLOCK_BOOTTIME
-clock does include the time during which the system is suspended.
-This is useful for applications that need to be suspend-aware.
-.B CLOCK_REALTIME
-is not suitable for such applications, since that clock is affected
-by discontinuous changes to the system clock.
-.TP
-.BR CLOCK_REALTIME_ALARM " (since Linux 3.0)"
-.\" commit 9a7adcf5c6dea63d2e47e6f6d2f7a6c9f48b9337
-This clock is like
-.BR CLOCK_REALTIME ,
-but will wake the system if it is suspended.
-The caller must have the
-.B CAP_WAKE_ALARM
-capability in order to set a timer against this clock.
-.TP
-.BR CLOCK_BOOTTIME_ALARM " (since Linux 3.0)"
-.\" commit 9a7adcf5c6dea63d2e47e6f6d2f7a6c9f48b9337
-This clock is like
-.BR CLOCK_BOOTTIME ,
-but will wake the system if it is suspended.
-The caller must have the
-.B CAP_WAKE_ALARM
-capability in order to set a timer against this clock.
-.TP
-.BR CLOCK_TAI " (since Linux 3.10)"
-A system-wide clock derived from wall-clock time but counting leap seconds.
-.P
-See
-.BR clock_getres (2)
-for some further details on the above clocks.
-.P
-As well as the above values,
-.I clockid
-can be specified as the
-.I clockid
-returned by a call to
-.BR clock_getcpuclockid (3)
-or
-.BR pthread_getcpuclockid (3).
-.P
-The
-.I sevp
-argument points to a
-.I sigevent
-structure that specifies how the caller
-should be notified when the timer expires.
-For the definition and general details of this structure, see
-.BR sigevent (3type).
-.P
-The
-.I sevp.sigev_notify
-field can have the following values:
-.TP
-.B SIGEV_NONE
-Don't asynchronously notify when the timer expires.
-Progress of the timer can be monitored using
-.BR timer_gettime (2).
-.TP
-.B SIGEV_SIGNAL
-Upon timer expiration, generate the signal
-.I sigev_signo
-for the process.
-See
-.BR sigevent (3type)
-for general details.
-The
-.I si_code
-field of the
-.I siginfo_t
-structure will be set to
-.BR SI_TIMER .
-At any point in time,
-at most one signal is queued to the process for a given timer; see
-.BR timer_getoverrun (2)
-for more details.
-.TP
-.B SIGEV_THREAD
-Upon timer expiration, invoke
-.I sigev_notify_function
-as if it were the start function of a new thread.
-See
-.BR sigevent (3type)
-for details.
-.TP
-.BR SIGEV_THREAD_ID " (Linux-specific)"
-As for
-.BR SIGEV_SIGNAL ,
-but the signal is targeted at the thread whose ID is given in
-.IR sigev_notify_thread_id ,
-which must be a thread in the same process as the caller.
-The
-.I sigev_notify_thread_id
-field specifies a kernel thread ID, that is, the value returned by
-.BR clone (2)
-or
-.BR gettid (2).
-This flag is intended only for use by threading libraries.
-.P
-Specifying
-.I sevp
-as NULL is equivalent to specifying a pointer to a
-.I sigevent
-structure in which
-.I sigev_notify
-is
-.BR SIGEV_SIGNAL ,
-.I sigev_signo
-is
-.BR SIGALRM ,
-and
-.I sigev_value.sival_int
-is the timer ID.
-.SH RETURN VALUE
-On success,
-.BR timer_create ()
-returns 0, and the ID of the new timer is placed in
-.IR *timerid .
-On failure, \-1 is returned, and
-.I errno
-is set to indicate the error.
-.SH ERRORS
-.TP
-.B EAGAIN
-Temporary error during kernel allocation of timer structures.
-.TP
-.B EINVAL
-Clock ID,
-.IR sigev_notify ,
-.IR sigev_signo ,
-or
-.I sigev_notify_thread_id
-is invalid.
-.TP
-.B ENOMEM
-.\" glibc layer: malloc()
-Could not allocate memory.
-.TP
-.B ENOTSUP
-The kernel does not support creating a timer against this
-.IR clockid .
-.TP
-.B EPERM
-.I clockid
-was
-.B CLOCK_REALTIME_ALARM
-or
-.B CLOCK_BOOTTIME_ALARM
-but the caller did not have the
-.B CAP_WAKE_ALARM
-capability.
-.SH VERSIONS
-.SS C library/kernel differences
-Part of the implementation of the POSIX timers API is provided by glibc.
-.\" See nptl/sysdeps/unix/sysv/linux/timer_create.c
-In particular:
-.IP \[bu] 3
-Much of the functionality for
-.B SIGEV_THREAD
-is implemented within glibc, rather than the kernel.
-(This is necessarily so,
-since the thread involved in handling the notification is one
-that must be managed by the C library POSIX threads implementation.)
-Although the notification delivered to the process is via a thread,
-internally the NPTL implementation uses a
-.I sigev_notify
-value of
-.B SIGEV_THREAD_ID
-along with a real-time signal that is reserved by the implementation (see
-.BR nptl (7)).
-.IP \[bu]
-The implementation of the default case where
-.I evp
-is NULL is handled inside glibc,
-which invokes the underlying system call with a suitably populated
-.I sigevent
-structure.
-.IP \[bu]
-The timer IDs presented at user level are maintained by glibc,
-which maps these IDs to the timer IDs employed by the kernel.
-.\" See the glibc source file kernel-posix-timers.h for the structure
-.\" that glibc uses to map user-space timer IDs to kernel timer IDs
-.\" The kernel-level timer ID is exposed via siginfo.si_tid.
-.SH STANDARDS
-POSIX.1-2008.
-.SH HISTORY
-Linux 2.6.
-POSIX.1-2001.
-.P
-Prior to Linux 2.6,
-glibc provided an incomplete user-space implementation
-.RB ( CLOCK_REALTIME
-timers only) using POSIX threads,
-and before glibc 2.17,
-.\" glibc commit 93a78ac437ba44f493333d7e2a4b0249839ce460
-the implementation falls back to this technique on systems
-running kernels older than Linux 2.6.
-.SH NOTES
-A program may create multiple interval timers using
-.BR timer_create ().
-.P
-Timers are not inherited by the child of a
-.BR fork (2),
-and are disarmed and deleted during an
-.BR execve (2).
-.P
-The kernel preallocates a "queued real-time signal"
-for each timer created using
-.BR timer_create ().
-Consequently, the number of timers is limited by the
-.B RLIMIT_SIGPENDING
-resource limit (see
-.BR setrlimit (2)).
-.P
-The timers created by
-.BR timer_create ()
-are commonly known as "POSIX (interval) timers".
-The POSIX timers API consists of the following interfaces:
-.TP
-.BR timer_create ()
-Create a timer.
-.TP
-.BR timer_settime (2)
-Arm (start) or disarm (stop) a timer.
-.TP
-.BR timer_gettime (2)
-Fetch the time remaining until the next expiration of a timer,
-along with the interval setting of the timer.
-.TP
-.BR timer_getoverrun (2)
-Return the overrun count for the last timer expiration.
-.TP
-.BR timer_delete (2)
-Disarm and delete a timer.
-.P
-Since Linux 3.10, the
-.IR /proc/ pid /timers
-file can be used to list the POSIX timers for the process with PID
-.IR pid .
-See
-.BR proc (5)
-for further information.
-.P
-Since Linux 4.10,
-.\" baa73d9e478ff32d62f3f9422822b59dd9a95a21
-support for POSIX timers is a configurable option that is enabled by default.
-Kernel support can be disabled via the
-.B CONFIG_POSIX_TIMERS
-option.
-.SH EXAMPLES
-The program below takes two arguments: a sleep period in seconds,
-and a timer frequency in nanoseconds.
-The program establishes a handler for the signal it uses for the timer,
-blocks that signal,
-creates and arms a timer that expires with the given frequency,
-sleeps for the specified number of seconds,
-and then unblocks the timer signal.
-Assuming that the timer expired at least once while the program slept,
-the signal handler will be invoked,
-and the handler displays some information about the timer notification.
-The program terminates after one invocation of the signal handler.
-.P
-In the following example run, the program sleeps for 1 second,
-after creating a timer that has a frequency of 100 nanoseconds.
-By the time the signal is unblocked and delivered,
-there have been around ten million overruns.
-.P
-.in +4n
-.EX
-$ \fB./a.out 1 100\fP
-Establishing handler for signal 34
-Blocking signal 34
-timer ID is 0x804c008
-Sleeping for 1 seconds
-Unblocking signal 34
-Caught signal 34
- sival_ptr = 0xbfb174f4; *sival_ptr = 0x804c008
- overrun count = 10004886
-.EE
-.in
-.SS Program source
-\&
-.\" SRC BEGIN (timer_create.c)
-.EX
-#include <signal.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <time.h>
-#include <unistd.h>
-\&
-#define CLOCKID CLOCK_REALTIME
-#define SIG SIGRTMIN
-\&
-#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \e
- } while (0)
-\&
-static void
-print_siginfo(siginfo_t *si)
-{
- int or;
- timer_t *tidp;
-\&
- tidp = si\->si_value.sival_ptr;
-\&
- printf(" sival_ptr = %p; ", si\->si_value.sival_ptr);
- printf(" *sival_ptr = %#jx\en", (uintmax_t) *tidp);
-\&
- or = timer_getoverrun(*tidp);
- if (or == \-1)
- errExit("timer_getoverrun");
- else
- printf(" overrun count = %d\en", or);
-}
-\&
-static void
-handler(int sig, siginfo_t *si, void *uc)
-{
- /* Note: calling printf() from a signal handler is not safe
- (and should not be done in production programs), since
- printf() is not async\-signal\-safe; see signal\-safety(7).
- Nevertheless, we use printf() here as a simple way of
- showing that the handler was called. */
-\&
- printf("Caught signal %d\en", sig);
- print_siginfo(si);
- signal(sig, SIG_IGN);
-}
-\&
-int
-main(int argc, char *argv[])
-{
- timer_t timerid;
- sigset_t mask;
- long long freq_nanosecs;
- struct sigevent sev;
- struct sigaction sa;
- struct itimerspec its;
-\&
- if (argc != 3) {
- fprintf(stderr, "Usage: %s <sleep\-secs> <freq\-nanosecs>\en",
- argv[0]);
- exit(EXIT_FAILURE);
- }
-\&
- /* Establish handler for timer signal. */
-\&
- printf("Establishing handler for signal %d\en", SIG);
- sa.sa_flags = SA_SIGINFO;
- sa.sa_sigaction = handler;
- sigemptyset(&sa.sa_mask);
- if (sigaction(SIG, &sa, NULL) == \-1)
- errExit("sigaction");
-\&
- /* Block timer signal temporarily. */
-\&
- printf("Blocking signal %d\en", SIG);
- sigemptyset(&mask);
- sigaddset(&mask, SIG);
- if (sigprocmask(SIG_SETMASK, &mask, NULL) == \-1)
- errExit("sigprocmask");
-\&
- /* Create the timer. */
-\&
- sev.sigev_notify = SIGEV_SIGNAL;
- sev.sigev_signo = SIG;
- sev.sigev_value.sival_ptr = &timerid;
- if (timer_create(CLOCKID, &sev, &timerid) == \-1)
- errExit("timer_create");
-\&
- printf("timer ID is %#jx\en", (uintmax_t) timerid);
-\&
- /* Start the timer. */
-\&
- freq_nanosecs = atoll(argv[2]);
- its.it_value.tv_sec = freq_nanosecs / 1000000000;
- its.it_value.tv_nsec = freq_nanosecs % 1000000000;
- its.it_interval.tv_sec = its.it_value.tv_sec;
- its.it_interval.tv_nsec = its.it_value.tv_nsec;
-\&
- if (timer_settime(timerid, 0, &its, NULL) == \-1)
- errExit("timer_settime");
-\&
- /* Sleep for a while; meanwhile, the timer may expire
- multiple times. */
-\&
- printf("Sleeping for %d seconds\en", atoi(argv[1]));
- sleep(atoi(argv[1]));
-\&
- /* Unlock the timer signal, so that timer notification
- can be delivered. */
-\&
- printf("Unblocking signal %d\en", SIG);
- if (sigprocmask(SIG_UNBLOCK, &mask, NULL) == \-1)
- errExit("sigprocmask");
-\&
- exit(EXIT_SUCCESS);
-}
-.EE
-.\" SRC END
-.SH SEE ALSO
-.ad l
-.nh
-.BR clock_gettime (2),
-.BR setitimer (2),
-.BR timer_delete (2),
-.BR timer_getoverrun (2),
-.BR timer_settime (2),
-.BR timerfd_create (2),
-.BR clock_getcpuclockid (3),
-.BR pthread_getcpuclockid (3),
-.BR pthreads (7),
-.BR sigevent (3type),
-.BR signal (7),
-.BR time (7)