wait for child process to change state
pid_t waitpid(pid_t pid, int stat_loc, int options);
waitpid suspends the calling process until
one of its children changes state;
if a child process changed state prior to the call to
waitpid, return is immediate.
pid specifies a set of child processes for which status is requested.
is equal to (pid_t)-1, status is requested for any child process.
is greater than (pid_t)0, it specifies the process
of the child process for which status is requested.
is equal to (pid_t)0 status is requested for any child process whose
is equal to that of the calling process.
is less than (pid_t)-1, status is requested for any child process whose
is equal to the absolute value of pid.
returns because the status of a child process is available, then that
status may be evaluated with the macros defined by
If the calling process had specified a non-zero value
of stat_loc, the status of the child process will be stored in the
location pointed to by stat_loc.
argument is constructed from the bitwise inclusive OR of zero or more
of the following flags, defined in the header file sys/wait.h:
the status of any continued child process specified by pid,
whose status has not been reported since it continued (from a job control
stop), shall also be reported to the calling process.
waitpid will not suspend execution of the calling process if status
is not immediately available for one of the child processes specified by
keep the process whose status is returned in stat_loc in a waitable
The process may be waited for again with identical results.
the status of any child processes specified by pid^
that are stopped, and whose status has not yet been reported since
they stopped, shall also be reported to the calling process.
equal to WUNTRACED and pid^ equal to (pid_t)-1 is
identical to a call to
If waitpid returns because the status of a child process is available,
it returns the process
of the child process for which status is reported.
If waitpid was invoked with WNOHANG set in options,
it has at least one child process specified by pid for which
status is not available, and status is not available for any process
specified by pid, waitpid returns 0.
Otherwise, waitpid returns -1 and sets errno to identify the error.
In the following conditions, waitpid fails and sets errno to:
waitpid was interrupted due to the receipt of a signal sent by the
An invalid value was specified for
The process or process group specified by pid
does not exist or is not a child of the calling process
or can never be in the states specified by options.
Considerations for threads programming
While one thread is blocked, siblings might still be executing.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004