suspends the execution of the calling thread
until either at least the time specified in
has elapsed, or the delivery of a signal
that triggers the invocation of a handler in the calling thread or
that terminates the process.
If the call is interrupted by a signal handler,
returns -1, sets errno to
and writes the remaining time into the structure pointed to by
The value of
can then be used to call
again and complete the specified pause (but see NOTES).
is used to specify intervals of time with nanosecond precision.
It is defined as follows:
The value of the nanoseconds field must be in the range 0 to 999999999.
has the following advantages:
it provides a higher resolution for specifying the sleep interval;
POSIX.1 explicitly specifies that it
does not interact with signals;
and it makes the task of resuming a sleep that has been
interrupted by a signal handler easier.
On successfully sleeping for the requested interval,
If the call is interrupted by a signal handler or encounters an error,
then it returns -1, with
set to indicate the error.
Problem with copying information from user space.
The pause has been interrupted by a signal that was
delivered to the thread.
The remaining sleep time has been written
into *rem so that the thread can easily call
again and continue with the pause.
The value in the
field was not in the range 0 to 999999999 or
If the interval specified in
is not an exact multiple of the granularity underlying clock (see
then the interval will be rounded up to the next multiple.
Furthermore, after the sleep completes, there may still be a delay before
the CPU becomes free to once again execute the calling thread.
The fact that
sleeps for a relative interval can be problematic if the call
is repeatedly restarted after being interrupted by signals,
since the time between the interruptions and restarts of the call
will lead to drift in the time when the sleep finally completes.
This problem can be avoided by using
with an absolute time value.
POSIX.1 specifies that
should measure time against the
However, Linux measures the time using the
This probably does not matter, since the POSIX.1 specification for
says that discontinuous changes in
should not affect
Setting the value of the
have no effect on threads that are blocked waiting for a relative time
service based upon this clock, including the
Consequently, these time services shall expire when the requested relative
interval elapses, independently of the new or old value of the clock.
In order to support applications requiring much more precise pauses
(e.g., in order to control some time-critical hardware),
would handle pauses of up to 2 ms by busy waiting with microsecond
precision when called from a thread scheduled under a real-time policy
This special extension was removed in kernel 2.5.39,
hence is still present in
current 2.4 kernels, but not in 2.6 kernels.
In Linux 2.4, if
is stopped by a signal (e.g.,
then the call fails with the error
after the thread is resumed by a
If the system call is subsequently restarted,
then the time that the thread spent in the stopped state is
not counted against the sleep interval.