# restart_syscall

## NAME



           restart_syscall - restart a system call after interruption by a
           stop signal
    


## SYNOPSIS



           **long restart_syscall(void);**
    
           _Note_ : There is no glibc wrapper for this system call; see NOTES.
    


## DESCRIPTION



           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.
    


## RETURN VALUE



           The return value of **restart_syscall**() is the return value of
           whatever system call is being restarted.
    


## ERRORS



           _errno_ is set as per the errors for whatever system call is being
           restarted by **restart_syscall**().
    


## STANDARDS



           Linux.
    


## NOTES



           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.
    


* * *