1CLOCK_NANOSLEEP(P) POSIX Programmer's Manual CLOCK_NANOSLEEP(P)
2
6 clock_nanosleep - high resolution sleep with specifiable clock
7 (ADVANCED REALTIME)
8
10 #include <time.h>
11 int clock_nanosleep(clockid_t clock_id, int flags,
13 const struct timespec *rqtp, struct timespec *rmtp);
14
17 If the flag TIMER_ABSTIME is not set in the flags argument, the
18 clock_nanosleep() function shall cause the current thread to be sus‐
19 pended from execution until either the time interval specified by the
20 rqtp argument has elapsed, or a signal is delivered to the calling
21 thread and its action is to invoke a signal-catching function, or the
22 process is terminated. The clock used to measure the time shall be the
23 clock specified by clock_id.
24 If the flag TIMER_ABSTIME is set in the flags argument, the
26 clock_nanosleep() function shall cause the current thread to be sus‐
27 pended from execution until either the time value of the clock speci‐
28 fied by clock_id reaches the absolute time specified by the rqtp argu‐
29 ment, or a signal is delivered to the calling thread and its action is
30 to invoke a signal-catching function, or the process is terminated. If,
31 at the time of the call, the time value specified by rqtp is less than
32 or equal to the time value of the specified clock, then
33 clock_nanosleep() shall return immediately and the calling process
34 shall not be suspended.
35 The suspension time caused by this function may be longer than
37 requested because the argument value is rounded up to an integer multi‐
38 ple of the sleep resolution, or because of the scheduling of other
39 activity by the system. But, except for the case of being interrupted
40 by a signal, the suspension time for the relative clock_nanosleep()
41 function (that is, with the TIMER_ABSTIME flag not set) shall not be
42 less than the time interval specified by rqtp, as measured by the cor‐
43 responding clock. The suspension for the absolute clock_nanosleep()
44 function (that is, with the TIMER_ABSTIME flag set) shall be in effect
45 at least until the value of the corresponding clock reaches the abso‐
46 lute time specified by rqtp, except for the case of being interrupted
47 by a signal.
48 The use of the clock_nanosleep() function shall have no effect on the
50 action or blockage of any signal.
51 The clock_nanosleep() function shall fail if the clock_id argument
53 refers to the CPU-time clock of the calling thread. It is unspecified
54 whether clock_id values of other CPU-time clocks are allowed.
55
57 If the clock_nanosleep() function returns because the requested time
58 has elapsed, its return value shall be zero.
59 If the clock_nanosleep() function returns because it has been inter‐
61 rupted by a signal, it shall return the corresponding error value. For
62 the relative clock_nanosleep() function, if the rmtp argument is non-
63 NULL, the timespec structure referenced by it shall be updated to con‐
64 tain the amount of time remaining in the interval (the requested time
65 minus the time actually slept). If the rmtp argument is NULL, the
66 remaining time is not returned. The absolute clock_nanosleep() function
67 has no effect on the structure referenced by rmtp.
68 If clock_nanosleep() fails, it shall return the corresponding error
70 value.
71
73 The clock_nanosleep() function shall fail if:
74 EINTR The clock_nanosleep() function was interrupted by a signal.
76 EINVAL The rqtp argument specified a nanosecond value less than zero or
78 greater than or equal to 1000 million; or the TIMER_ABSTIME flag
79 was specified in flags and the rqtp argument is outside the
80 range for the clock specified by clock_id; or the clock_id argu‐
81 ment does not specify a known clock, or specifies the CPU-time
82 clock of the calling thread.
83 ENOTSUP
85 The clock_id argument specifies a clock for which
86 clock_nanosleep() is not supported, such as a CPU-time clock.
87 The following sections are informative.
90
92 None.
93
95 Calling clock_nanosleep() with the value TIMER_ABSTIME not set in the
96 flags argument and with a clock_id of CLOCK_REALTIME is equivalent to
97 calling nanosleep() with the same rqtp and rmtp arguments.
98
100 The nanosleep() function specifies that the system-wide clock
101 CLOCK_REALTIME is used to measure the elapsed time for this time ser‐
102 vice. However, with the introduction of the monotonic clock CLOCK_MONO‐
103 TONIC a new relative sleep function is needed to allow an application
104 to take advantage of the special characteristics of this clock.
105 There are many applications in which a process needs to be suspended
107 and then activated multiple times in a periodic way; for example, to
108 poll the status of a non-interrupting device or to refresh a display
109 device. For these cases, it is known that precise periodic activation
110 cannot be achieved with a relative sleep() or nanosleep() function
111 call. Suppose, for example, a periodic process that is activated at
112 time T0, executes for a while, and then wants to suspend itself until
113 time T0+ T, the period being T. If this process wants to use the
114 nanosleep() function, it must first call clock_gettime() to get the
115 current time, then calculate the difference between the current time
116 and T0+ T and, finally, call nanosleep() using the computed interval.
117 However, the process could be preempted by a different process between
118 the two function calls, and in this case the interval computed would be
119 wrong; the process would wake up later than desired. This problem would
120 not occur with the absolute clock_nanosleep() function, since only one
121 function call would be necessary to suspend the process until the
122 desired time. In other cases, however, a relative sleep is needed, and
123 that is why both functionalities are required.
124 Although it is possible to implement periodic processes using the
126 timers interface, this implementation would require the use of signals,
127 and the reservation of some signal numbers. In this regard, the reasons
128 for including an absolute version of the clock_nanosleep() function in
129 IEEE Std 1003.1-2001 are the same as for the inclusion of the relative
130 nanosleep().
131 It is also possible to implement precise periodic processes using
133 pthread_cond_timedwait(), in which an absolute timeout is specified
134 that takes effect if the condition variable involved is never signaled.
135 However, the use of this interface is unnatural, and involves perform‐
136 ing other operations on mutexes and condition variables that imply an
137 unnecessary overhead. Furthermore, pthread_cond_timedwait() is not
138 available in implementations that do not support threads.
139 Although the interface of the relative and absolute versions of the new
141 high resolution sleep service is the same clock_nanosleep() function,
142 the rmtp argument is only used in the relative sleep. This argument is
143 needed in the relative clock_nanosleep() function to reissue the func‐
144 tion call if it is interrupted by a signal, but it is not needed in the
145 absolute clock_nanosleep() function call; if the call is interrupted by
146 a signal, the absolute clock_nanosleep() function can be invoked again
147 with the same rqtp argument used in the interrupted call.
148
150 None.
151
153 clock_getres() , nanosleep() , pthread_cond_timedwait() , sleep() , the
154 Base Definitions volume of IEEE Std 1003.1-2001, <time.h>
155
157 Portions of this text are reprinted and reproduced in electronic form
158 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
159 -- Portable Operating System Interface (POSIX), The Open Group Base
160 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
161 Electrical and Electronics Engineers, Inc and The Open Group. In the
162 event of any discrepancy between this version and the original IEEE and
163 The Open Group Standard, the original IEEE and The Open Group Standard
164 is the referee document. The original Standard can be obtained online
165 at http://www.opengroup.org/unix/online.html .
166IEEE/The Open Group 2003 CLOCK_NANOSLEEP(P)