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.
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12 timer_getoverrun, timer_gettime, timer_settime — per-process timers
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15 #include <time.h>
16 int timer_getoverrun(timer_t timerid);
18 int timer_gettime(timer_t timerid, struct itimerspec *value);
19 int timer_settime(timer_t timerid, int flags,
20 const struct itimerspec *restrict value,
21 struct itimerspec *restrict ovalue);
22
24 The timer_gettime() function shall store the amount of time until the
25 specified timer, timerid, expires and the reload value of the timer
26 into the space pointed to by the value argument. The it_value member of
27 this structure shall contain the amount of time before the timer
28 expires, or zero if the timer is disarmed. This value is returned as
29 the interval until timer expiration, even if the timer was armed with
30 absolute time. The it_interval member of value shall contain the reload
31 value last set by timer_settime().
32 The timer_settime() function shall set the time until the next expira‐
34 tion of the timer specified by timerid from the it_value member of the
35 value argument and arm the timer if the it_value member of value is
36 non-zero. If the specified timer was already armed when timer_settime()
37 is called, this call shall reset the time until next expiration to the
38 value specified. If the it_value member of value is zero, the timer
39 shall be disarmed. The effect of disarming or resetting a timer with
40 pending expiration notifications is unspecified.
41 If the flag TIMER_ABSTIME is not set in the argument flags, timer_set‐
43 time() shall behave as if the time until next expiration is set to be
44 equal to the interval specified by the it_value member of value. That
45 is, the timer shall expire in it_value nanoseconds from when the call
46 is made. If the flag TIMER_ABSTIME is set in the argument flags,
47 timer_settime() shall behave as if the time until next expiration is
48 set to be equal to the difference between the absolute time specified
49 by the it_value member of value and the current value of the clock
50 associated with timerid. That is, the timer shall expire when the
51 clock reaches the value specified by the it_value member of value. If
52 the specified time has already passed, the function shall succeed and
53 the expiration notification shall be made.
54 The reload value of the timer shall be set to the value specified by
56 the it_interval member of value. When a timer is armed with a non-zero
57 it_interval, a periodic (or repetitive) timer is specified.
58 Time values that are between two consecutive non-negative integer mul‐
60 tiples of the resolution of the specified timer shall be rounded up to
61 the larger multiple of the resolution. Quantization error shall not
62 cause the timer to expire earlier than the rounded time value.
63 If the argument ovalue is not NULL, the timer_settime() function shall
65 store, in the location referenced by ovalue, a value representing the
66 previous amount of time before the timer would have expired, or zero if
67 the timer was disarmed, together with the previous timer reload value.
68 Timers shall not expire before their scheduled time.
69 Only a single signal shall be queued to the process for a given timer
71 at any point in time. When a timer for which a signal is still pending
72 expires, no signal shall be queued, and a timer overrun shall occur.
73 When a timer expiration signal is delivered to or accepted by a
74 process, the timer_getoverrun() function shall return the timer expira‐
75 tion overrun count for the specified timer. The overrun count returned
76 contains the number of extra timer expirations that occurred between
77 the time the signal was generated (queued) and when it was delivered or
78 accepted, up to but not including an implementation-defined maximum of
79 {DELAYTIMER_MAX}. If the number of such extra expirations is greater
80 than or equal to {DELAYTIMER_MAX}, then the overrun count shall be set
81 to {DELAYTIMER_MAX}. The value returned by timer_getoverrun() shall
82 apply to the most recent expiration signal delivery or acceptance for
83 the timer. If no expiration signal has been delivered for the timer,
84 the return value of timer_getoverrun() is unspecified.
85 The behavior is undefined if the value specified by the timerid argu‐
87 ment to timer_getoverrun(), timer_gettime(), or timer_settime() does
88 not correspond to a timer ID returned by timer_create() but not yet
89 deleted by timer_delete().
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92 If the timer_getoverrun() function succeeds, it shall return the timer
93 expiration overrun count as explained above.
94 If the timer_gettime() or timer_settime() functions succeed, a value of
96 0 shall be returned.
97 If an error occurs for any of these functions, the value -1 shall be
99 returned, and errno set to indicate the error.
100
102 The timer_settime() function shall fail if:
103 EINVAL A value structure specified a nanosecond value less than zero or
105 greater than or equal to 1000 million, and the it_value member
106 of that structure did not specify zero seconds and nanoseconds.
107 The timer_settime() function may fail if:
109 EINVAL The it_interval member of value is not zero and the timer was
111 created with notification by creation of a new thread
112 (sigev_sigev_notify was SIGEV_THREAD) and a fixed stack address
113 has been set in the thread attribute pointed to by
114 sigev_notify_attributes.
115 The following sections are informative.
117
119 None.
120
122 Using fixed stack addresses is problematic when timer expiration is
123 signaled by the creation of a new thread. Since it cannot be assumed
124 that the thread created for one expiration is finished before the next
125 expiration of the timer, it could happen that two threads use the same
126 memory as a stack at the same time. This is invalid and produces unde‐
127 fined results.
128
130 Practical clocks tick at a finite rate, with rates of 100 hertz and
131 1000 hertz being common. The inverse of this tick rate is the clock
132 resolution, also called the clock granularity, which in either case is
133 expressed as a time duration, being 10 milliseconds and 1 millisecond
134 respectively for these common rates. The granularity of practical
135 clocks implies that if one reads a given clock twice in rapid succes‐
136 sion, one may get the same time value twice; and that timers must wait
137 for the next clock tick after the theoretical expiration time, to
138 ensure that a timer never returns too soon. Note also that the granu‐
139 larity of the clock may be significantly coarser than the resolution of
140 the data format used to set and get time and interval values. Also note
141 that some implementations may choose to adjust time and/or interval
142 values to exactly match the ticks of the underlying clock.
143 This volume of POSIX.1‐2017 defines functions that allow an application
145 to determine the implementation-supported resolution for the clocks and
146 requires an implementation to document the resolution supported for
147 timers and nanosleep() if they differ from the supported clock resolu‐
148 tion. This is more of a procurement issue than a runtime application
149 issue.
150 If an implementation detects that the value specified by the timerid
152 argument to timer_getoverrun(), timer_gettime(), or timer_settime()
153 does not correspond to a timer ID returned by timer_create() but not
154 yet deleted by timer_delete(), it is recommended that the function
155 should fail and report an [EINVAL] error.
156
158 None.
159
161 clock_getres(), timer_create()
162 The Base Definitions volume of POSIX.1‐2017, <time.h>
164
166 Portions of this text are reprinted and reproduced in electronic form
167 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
168 table Operating System Interface (POSIX), The Open Group Base Specifi‐
169 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
170 Electrical and Electronics Engineers, Inc and The Open Group. In the
171 event of any discrepancy between this version and the original IEEE and
172 The Open Group Standard, the original IEEE and The Open Group Standard
173 is the referee document. The original Standard can be obtained online
174 at http://www.opengroup.org/unix/online.html .
175 Any typographical or formatting errors that appear in this page are
177 most likely to have been introduced during the conversion of the source
178 files to man page format. To report such errors, see https://www.ker‐
179 nel.org/doc/man-pages/reporting_bugs.html .
180IEEE/The Open Group 2017 TIMER_GETOVERRUN(3P)