1TIMER_GETOVERRUN(P) POSIX Programmer's Manual TIMER_GETOVERRUN(P)
2
6 timer_getoverrun, timer_gettime, timer_settime - per-process timers
7 (REALTIME)
8
10 #include <time.h>
11 int timer_getoverrun(timer_t timerid);
13 int timer_gettime(timer_t timerid, struct itimerspec *value);
14 int timer_settime(timer_t timerid, int flags,
15 const struct itimerspec *restrict value,
16 struct itimerspec *restrict ovalue);
17
20 The timer_gettime() function shall store the amount of time until the
21 specified timer, timerid, expires and the reload value of the timer
22 into the space pointed to by the value argument. The it_value member of
23 this structure shall contain the amount of time before the timer
24 expires, or zero if the timer is disarmed. This value is returned as
25 the interval until timer expiration, even if the timer was armed with
26 absolute time. The it_interval member of value shall contain the reload
27 value last set by timer_settime().
28 The timer_settime() function shall set the time until the next expira‐
30 tion of the timer specified by timerid from the it_value member of the
31 value argument and arm the timer if the it_value member of value is
32 non-zero. If the specified timer was already armed when timer_settime()
33 is called, this call shall reset the time until next expiration to the
34 value specified. If the it_value member of value is zero, the timer
35 shall be disarmed. The effect of disarming or resetting a timer with
36 pending expiration notifications is unspecified.
37 If the flag TIMER_ABSTIME is not set in the argument flags, timer_set‐
39 time() shall behave as if the time until next expiration is set to be
40 equal to the interval specified by the it_value member of value. That
41 is, the timer shall expire in it_value nanoseconds from when the call
42 is made. If the flag TIMER_ABSTIME is set in the argument flags,
43 timer_settime() shall behave as if the time until next expiration is
44 set to be equal to the difference between the absolute time specified
45 by the it_value member of value and the current value of the clock
46 associated with timerid. That is, the timer shall expire when the
47 clock reaches the value specified by the it_value member of value. If
48 the specified time has already passed, the function shall succeed and
49 the expiration notification shall be made.
50 The reload value of the timer shall be set to the value specified by
52 the it_interval member of value. When a timer is armed with a non-zero
53 it_interval, a periodic (or repetitive) timer is specified.
54 Time values that are between two consecutive non-negative integer mul‐
56 tiples of the resolution of the specified timer shall be rounded up to
57 the larger multiple of the resolution. Quantization error shall not
58 cause the timer to expire earlier than the rounded time value.
59 If the argument ovalue is not NULL, the timer_settime() function shall
61 store, in the location referenced by ovalue, a value representing the
62 previous amount of time before the timer would have expired, or zero if
63 the timer was disarmed, together with the previous timer reload value.
64 Timers shall not expire before their scheduled time.
65 Only a single signal shall be queued to the process for a given timer
67 at any point in time. When a timer for which a signal is still pending
68 expires, no signal shall be queued, and a timer overrun shall occur.
69 When a timer expiration signal is delivered to or accepted by a
70 process, if the implementation supports the Realtime Signals Extension,
71 the timer_getoverrun() function shall return the timer expiration over‐
72 run count for the specified timer. The overrun count returned contains
73 the number of extra timer expirations that occurred between the time
74 the signal was generated (queued) and when it was delivered or
75 accepted, up to but not including an implementation-defined maximum of
76 {DELAYTIMER_MAX}. If the number of such extra expirations is greater
77 than or equal to {DELAYTIMER_MAX}, then the overrun count shall be set
78 to {DELAYTIMER_MAX}. The value returned by timer_getoverrun() shall
79 apply to the most recent expiration signal delivery or acceptance for
80 the timer. If no expiration signal has been delivered for the timer,
81 or if the Realtime Signals Extension is not supported, the return value
82 of timer_getoverrun() is unspecified.
83
85 If the timer_getoverrun() function succeeds, it shall return the timer
86 expiration overrun count as explained above.
87 If the timer_gettime() or timer_settime() functions succeed, a value of
89 0 shall be returned.
90 If an error occurs for any of these functions, the value -1 shall be
92 returned, and errno set to indicate the error.
93
95 The timer_getoverrun(), timer_gettime(), and timer_settime() functions
96 shall fail if:
97 EINVAL The timerid argument does not correspond to an ID returned by
99 timer_create() but not yet deleted by timer_delete().
100 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 following sections are informative.
110
112 None.
113
115 None.
116
118 Practical clocks tick at a finite rate, with rates of 100 hertz and
119 1000 hertz being common. The inverse of this tick rate is the clock
120 resolution, also called the clock granularity, which in either case is
121 expressed as a time duration, being 10 milliseconds and 1 millisecond
122 respectively for these common rates. The granularity of practical
123 clocks implies that if one reads a given clock twice in rapid succes‐
124 sion, one may get the same time value twice; and that timers must wait
125 for the next clock tick after the theoretical expiration time, to
126 ensure that a timer never returns too soon. Note also that the granu‐
127 larity of the clock may be significantly coarser than the resolution of
128 the data format used to set and get time and interval values. Also note
129 that some implementations may choose to adjust time and/or interval
130 values to exactly match the ticks of the underlying clock.
131 This volume of IEEE Std 1003.1-2001 defines functions that allow an
133 application to determine the implementation-supported resolution for
134 the clocks and requires an implementation to document the resolution
135 supported for timers and nanosleep() if they differ from the supported
136 clock resolution. This is more of a procurement issue than a runtime
137 application issue.
138
140 None.
141
143 clock_getres() , timer_create() , the Base Definitions volume of
144 IEEE Std 1003.1-2001, <time.h>
145
147 Portions of this text are reprinted and reproduced in electronic form
148 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
149 -- Portable Operating System Interface (POSIX), The Open Group Base
150 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
151 Electrical and Electronics Engineers, Inc and The Open Group. In the
152 event of any discrepancy between this version and the original IEEE and
153 The Open Group Standard, the original IEEE and The Open Group Standard
154 is the referee document. The original Standard can be obtained online
155 at http://www.opengroup.org/unix/online.html .
156IEEE/The Open Group 2003 TIMER_GETOVERRUN(P)