wait waitpid wait4 wait3 - wait for process termination
system call provides a more general interface for programs that need to wait for certain child processes, that need resource utilization statistics accumulated by child processes, or that require options. The other wait functions are implemented using wait4 (.);
The Fa wpid argument specifies the set of child processes for which to wait. If Fa wpid is -1, the call waits for any child process. If Fa wpid is 0, the call waits for any child process in the process group of the caller. If Fa wpid is greater than zero, the call waits for the process with process id Fa wpid . If Fa wpid is less than -1, the call waits for any process whose process group id equals the absolute value of Fa wpid .
The Fa status argument is defined below.
The Fa options argument contains the bitwise OR of any of the following options. The WCONTINUED option indicates that children of the current process that have continued from a job control stop, by receiving a SIGCONT signal, should also have their status reported. The WNOHANG option is used to indicate that the call should not block if there are no processes that wish to report status. If the WUNTRACED option is set, children of the current process that are stopped due to a SIGTTIN , SIGTTOU , SIGTSTP or SIGSTOP signal also have their status reported. The WSTOPPED option is an alias for WUNTRACED The WNOWAIT option keeps the process whose status is returned in a waitable state. The process may be waited for again after this call completes.
If Fa rusage is non-zero, a summary of the resources used by the terminated process and all its children is returned (this information is currently not available for stopped or continued processes).
option is specified and no processes
wish to report status,
returns a process id of 0.
function is identical to wait4 ();
with an Fa rusage value of zero. The older wait3 ();
call is the same as wait4 ();
with a Fa wpid value of -1.
The following macros may be used to test the manner of exit of the process. One of the first three macros will evaluate to a non-zero (true) value:
Depending on the values of those macros, the following macros produce the remaining status information about the child process:
If a parent process terminates without waiting for all of its child processes to terminate, the remaining child processes are assigned the parent process 1 ID (the init process ID).
If a signal is caught while any of the
calls are pending, the call may be interrupted or restarted when the signal-catching routine returns, depending on the options in effect for the signal; see discussion of SA_RESTART in sigaction(2).
The implementation queues one
signal for each child process whose
status has changed, if
returns because the status of a child process is available, the pending SIGCHLD signal associated with the process ID of the child process will be discarded. Any other pending SIGCHLD signals remain pending.
returns because the status of a child process is available, the pending SIGCHLD signal will be cleared unless another status of the child process is available.
or waitpid ();
returns due to a stopped, continued, or terminated child process, the process ID of the child is returned to the calling process. If there are no children not previously awaited, -1 is returned with errno set to Er ECHILD . Otherwise, if WNOHANG is specified and there are no stopped, continued or exited children, 0 is returned. If an error is detected or a caught signal aborts the call, a value of -1 is returned and errno is set to indicate the error.
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Created 1996-2021 by Maxim Chirkov
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