1GETITIMER(3P) POSIX Programmer's Manual GETITIMER(3P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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12 getitimer, setitimer - get and set value of interval timer
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15 #include <sys/time.h>
16 int getitimer(int which, struct itimerval *value);
18 int setitimer(int which, const struct itimerval *restrict value,
19 struct itimerval *restrict ovalue);
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23 The getitimer() function shall store the current value of the timer
24 specified by which into the structure pointed to by value. The
25 setitimer() function shall set the timer specified by which to the
26 value specified in the structure pointed to by value, and if ovalue is
27 not a null pointer, store the previous value of the timer in the struc‐
28 ture pointed to by ovalue.
29 A timer value is defined by the itimerval structure, specified in
31 <sys/time.h>. If it_value is non-zero, it shall indicate the time to
32 the next timer expiration. If it_interval is non-zero, it shall specify
33 a value to be used in reloading it_value when the timer expires. Set‐
34 ting it_value to 0 shall disable a timer, regardless of the value of
35 it_interval. Setting it_interval to 0 shall disable a timer after its
36 next expiration (assuming it_value is non-zero).
37 Implementations may place limitations on the granularity of timer val‐
39 ues. For each interval timer, if the requested timer value requires a
40 finer granularity than the implementation supports, the actual timer
41 value shall be rounded up to the next supported value.
42 An XSI-conforming implementation provides each process with at least
44 three interval timers, which are indicated by the which argument:
45 ITIMER_REAL
47 Decrements in real time. A SIGALRM signal is delivered when this
48 timer expires.
49 ITIMER_VIRTUAL
51 Decrements in process virtual time. It runs only when the
52 process is executing. A SIGVTALRM signal is delivered when it
53 expires.
54 ITIMER_PROF
56 Decrements both in process virtual time and when the system is
57 running on behalf of the process. It is designed to be used by
58 interpreters in statistically profiling the execution of inter‐
59 preted programs. Each time the ITIMER_PROF timer expires, the
60 SIGPROF signal is delivered.
61 The interaction between setitimer() and any of alarm(), sleep(), or
64 usleep() is unspecified.
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67 Upon successful completion, getitimer() or setitimer() shall return 0;
68 otherwise, -1 shall be returned and errno set to indicate the error.
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71 The setitimer() function shall fail if:
72 EINVAL The value argument is not in canonical form. (In canonical form,
74 the number of microseconds is a non-negative integer less than
75 1000000 and the number of seconds is a non-negative integer.)
76 The getitimer() and setitimer() functions may fail if:
79 EINVAL The which argument is not recognized.
81 The following sections are informative.
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86 None.
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89 None.
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92 None.
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95 None.
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98 alarm(), sleep(), timer_getoverrun(), ualarm(), usleep(), the Base Def‐
99 initions volume of IEEE Std 1003.1-2001, <signal.h>, <sys/time.h>
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102 Portions of this text are reprinted and reproduced in electronic form
103 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
104 -- Portable Operating System Interface (POSIX), The Open Group Base
105 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
106 Electrical and Electronics Engineers, Inc and The Open Group. In the
107 event of any discrepancy between this version and the original IEEE and
108 The Open Group Standard, the original IEEE and The Open Group Standard
109 is the referee document. The original Standard can be obtained online
110 at http://www.opengroup.org/unix/online.html .
111IEEE/The Open Group 2003 GETITIMER(3P)