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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
RESTART_SYSCALL(2) Linux Programmer's Manual RESTART_SYSCALL(2)
restart_syscall - restart a system call after interruption by a stop
signal
int restart_syscall(void);
Note: There is no glibc wrapper for this system call; see NOTES.
The restart_syscall() system call is used to restart certain system
calls after a process that was stopped by a signal (e.g., SIGSTOP or
SIGTSTP) is later resumed after receiving a SIGCONT signal. This
system call is designed only for internal use by the kernel.
restart_syscall() is used for restarting only those system calls
that, when restarted, should adjust their time-related parameters—
namely poll(2) (since Linux 2.6.24), nanosleep(2) (since Linux 2.6),
clock_nanosleep(2) (since Linux 2.6), and futex(2), when employed
with the FUTEX_WAIT (since Linux 2.6.22) and FUTEX_WAIT_BITSET (since
Linux 2.6.31) operations. restart_syscall() restarts the interrupted
system call with a time argument that is suitably adjusted to account
for the time that has already elapsed (including the time where the
process was stopped by a signal). Without the restart_syscall()
mechanism, restarting these system calls would not correctly deduct
the already elapsed time when the process continued execution.
The return value of restart_syscall() is the return value of whatever
system call is being restarted.
errno is set as per the errors for whatever system call is being
restarted by restart_syscall().
The restart_syscall() system call is present since Linux 2.6.
This system call is Linux-specific.
There is no glibc wrapper for this system call, because it is
intended for use only by the kernel and should never be called by
applications.
The kernel uses restart_syscall() to ensure that when a system call
is restarted after a process has been stopped by a signal and then
resumed by SIGCONT, then the time that the process spent in the
stopped state is counted against the timeout interval specified in
the original system call. In the case of system calls that take a
timeout argument and automatically restart after a stop signal plus
SIGCONT, but which do not have the restart_syscall() mechanism built
in, then, after the process resumes execution, the time that the
process spent in the stop state is not counted against the timeout
value. Notable examples of system calls that suffer this problem are
ppoll(2), select(2), and pselect(2).
From user space, the operation of restart_syscall() is largely
invisible: to the process that made the system call that is
restarted, it appears as though that system call executed and
returned in the usual fashion.
sigaction(2), sigreturn(2), signal(7)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2016-10-08 RESTART_SYSCALL(2)
Pages that refer to this page: clock_nanosleep(2), futex(2), nanosleep(2), poll(2), ptrace(2), select(2), sigaction(2), sigreturn(2), syscalls(2), signal(7)