1TIMER_GETOVERRUN(3P) POSIX Programmer's Manual TIMER_GETOVERRUN(3P)
2
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.
10
13 timer_getoverrun, timer_gettime, timer_settime — per-process timers
14
16 #include <time.h>
17 int timer_getoverrun(timer_t timerid);
19 int timer_gettime(timer_t timerid, struct itimerspec *value);
20 int timer_settime(timer_t timerid, int flags,
21 const struct itimerspec *restrict value,
22 struct itimerspec *restrict ovalue);
23
25 The timer_gettime() function shall store the amount of time until the
26 specified timer, timerid, expires and the reload value of the timer
27 into the space pointed to by the value argument. The it_value member of
28 this structure shall contain the amount of time before the timer
29 expires, or zero if the timer is disarmed. This value is returned as
30 the interval until timer expiration, even if the timer was armed with
31 absolute time. The it_interval member of value shall contain the reload
32 value last set by timer_settime().
33 The timer_settime() function shall set the time until the next expira‐
35 tion of the timer specified by timerid from the it_value member of the
36 value argument and arm the timer if the it_value member of value is
37 non-zero. If the specified timer was already armed when timer_settime()
38 is called, this call shall reset the time until next expiration to the
39 value specified. If the it_value member of value is zero, the timer
40 shall be disarmed. The effect of disarming or resetting a timer with
41 pending expiration notifications is unspecified.
42 If the flag TIMER_ABSTIME is not set in the argument flags, timer_set‐
44 time() shall behave as if the time until next expiration is set to be
45 equal to the interval specified by the it_value member of value. That
46 is, the timer shall expire in it_value nanoseconds from when the call
47 is made. If the flag TIMER_ABSTIME is set in the argument flags,
48 timer_settime() shall behave as if the time until next expiration is
49 set to be equal to the difference between the absolute time specified
50 by the it_value member of value and the current value of the clock
51 associated with timerid. That is, the timer shall expire when the
52 clock reaches the value specified by the it_value member of value. If
53 the specified time has already passed, the function shall succeed and
54 the expiration notification shall be made.
55 The reload value of the timer shall be set to the value specified by
57 the it_interval member of value. When a timer is armed with a non-zero
58 it_interval, a periodic (or repetitive) timer is specified.
59 Time values that are between two consecutive non-negative integer mul‐
61 tiples of the resolution of the specified timer shall be rounded up to
62 the larger multiple of the resolution. Quantization error shall not
63 cause the timer to expire earlier than the rounded time value.
64 If the argument ovalue is not NULL, the timer_settime() function shall
66 store, in the location referenced by ovalue, a value representing the
67 previous amount of time before the timer would have expired, or zero if
68 the timer was disarmed, together with the previous timer reload value.
69 Timers shall not expire before their scheduled time.
70 Only a single signal shall be queued to the process for a given timer
72 at any point in time. When a timer for which a signal is still pending
73 expires, no signal shall be queued, and a timer overrun shall occur.
74 When a timer expiration signal is delivered to or accepted by a
75 process, the timer_getoverrun() function shall return the timer expira‐
76 tion overrun count for the specified timer. The overrun count returned
77 contains the number of extra timer expirations that occurred between
78 the time the signal was generated (queued) and when it was delivered or
79 accepted, up to but not including an implementation-defined maximum of
80 {DELAYTIMER_MAX}. If the number of such extra expirations is greater
81 than or equal to {DELAYTIMER_MAX}, then the overrun count shall be set
82 to {DELAYTIMER_MAX}. The value returned by timer_getoverrun() shall
83 apply to the most recent expiration signal delivery or acceptance for
84 the timer. If no expiration signal has been delivered for the timer,
85 the return value of timer_getoverrun() is unspecified.
86
88 If the timer_getoverrun() function succeeds, it shall return the timer
89 expiration overrun count as explained above.
90 If the timer_gettime() or timer_settime() functions succeed, a value of
92 0 shall be returned.
93 If an error occurs for any of these functions, the value −1 shall be
95 returned, and errno set to indicate the error.
96
98 The timer_settime() function shall fail if:
99 EINVAL A value structure specified a nanosecond value less than zero or
101 greater than or equal to 1000 million, and the it_value member
102 of that structure did not specify zero seconds and nanoseconds.
103 These functions may fail if:
105 EINVAL The timerid argument does not correspond to an ID returned by
107 timer_create() but not yet deleted by timer_delete().
108 The timer_settime() function may fail if:
110 EINVAL The it_interval member of value is not zero and the timer was
112 created with notification by creation of a new thread
113 (sigev_sigev_notify was SIGEV_THREAD) and a fixed stack address
114 has been set in the thread attribute pointed to by
115 sigev_notify_attributes.
116 The following sections are informative.
118
120 None.
121
123 Using fixed stack addresses is problematic when timer expiration is
124 signaled by the creation of a new thread. Since it cannot be assumed
125 that the thread created for one expiration is finished before the next
126 expiration of the timer, it could happen that two threads use the same
127 memory as a stack at the same time. This is invalid and produces unde‐
128 fined results.
129
131 Practical clocks tick at a finite rate, with rates of 100 hertz and
132 1000 hertz being common. The inverse of this tick rate is the clock
133 resolution, also called the clock granularity, which in either case is
134 expressed as a time duration, being 10 milliseconds and 1 millisecond
135 respectively for these common rates. The granularity of practical
136 clocks implies that if one reads a given clock twice in rapid succes‐
137 sion, one may get the same time value twice; and that timers must wait
138 for the next clock tick after the theoretical expiration time, to
139 ensure that a timer never returns too soon. Note also that the granu‐
140 larity of the clock may be significantly coarser than the resolution of
141 the data format used to set and get time and interval values. Also note
142 that some implementations may choose to adjust time and/or interval
143 values to exactly match the ticks of the underlying clock.
144 This volume of POSIX.1‐2008 defines functions that allow an application
146 to determine the implementation-supported resolution for the clocks and
147 requires an implementation to document the resolution supported for
148 timers and nanosleep() if they differ from the supported clock resolu‐
149 tion. This is more of a procurement issue than a runtime application
150 issue.
151
153 None.
154
156 clock_getres(), timer_create()
157 The Base Definitions volume of POSIX.1‐2008, <time.h>
159
161 Portions of this text are reprinted and reproduced in electronic form
162 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
163 -- Portable Operating System Interface (POSIX), The Open Group Base
164 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
165 cal and Electronics Engineers, Inc and The Open Group. (This is
166 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
167 event of any discrepancy between this version and the original IEEE and
168 The Open Group Standard, the original IEEE and The Open Group Standard
169 is the referee document. The original Standard can be obtained online
170 at http://www.unix.org/online.html .
171 Any typographical or formatting errors that appear in this page are
173 most likely to have been introduced during the conversion of the source
174 files to man page format. To report such errors, see https://www.ker‐
175 nel.org/doc/man-pages/reporting_bugs.html .
176IEEE/The Open Group 2013 TIMER_GETOVERRUN(3P)