HP-UX Reference (11i v3 07/02) - 2 System Calls (vol 5)

w
wait(2) wait(2)
NAME
wait(), waitpid() - wait for child process to stop or terminate
SYNOPSIS
#include <sys/types.h>
#include <sys/wait.h>
pid_t wait(
int *
stat_loc
);
pid_t waitpid(
pid_t
pid,
int *
stat_loc,
int
options
);
DESCIPTION
The wait() and waitpid() functions obtain status information pertaining to one of the caller’s child
processes. Various options permit status information to be obtained for child processes that have ter-
minated or stopped. If status information is available for two or more child processes, the order in which
their status is reported is unspecified.
The wait() function suspends execution of the calling thread until status information for one of the ter-
minated child processes of the calling process is available, or until delivery of a signal whose action is either
to execute a signal-catching function or to terminate the process. If more than one thread is suspended in
wait() or waitpid() awaiting termination of the same process, exactly one thread returns the process
status at the time of the target process termination. If status information is available prior to the call to
wait(), return is immediate.
The waitpid() function is equivalent to wait() if the pid argument is (pid_t)-1 and the options
argument is 0. Otherwise, its behavior is modified by the values of the pid and options arguments.
Note that if the parent process terminates without waiting for its child processes to terminate, these
processes are adopted by and recognize the initialization process as their parent.
The pid argument specifies the child processes for which status is requested. The
waitpid() function
only returns the status of a child process from this set:
• If pid is equal to
(pid_t)-1, status is requested for any child process. In this respect,
waitpid()
is equivalent to wait().
• If pid is greater than 0, it specifies the process ID of a single child process for which status is
requested.
• If pid is 0, status is requested for any child process whose process group ID is equal to that of the cal-
ling process.
• If pid is less than
(pid_t)-1, status is requested for any child process whose process group ID is
equal to the absolute value of pid.
The stat_loc argument is the address where status of the specified child processes is placed.
The options argument is constructed from the bitwise-inclusive OR of zero or more of the following flags
defined in the <sys/wait.h> header file.
WCONTINUED The waitpid() function reports the status of any continued child process specified
by pid whose status has not been reported since it continued from a job control stop.
WNOHANG The waitpid() function does not suspend execution of the calling thread if status is
not immediately available for one of the child processes specified by pid.
WNOWAIT HP-UX EXTENSION: Keep the process whose status is returned in stat_loc in a wait-
able state. The process may be waited for again with identical results, provided the
state of the process doesn’t change in the interim.
WUNTRACED The status of any child processes specified by pid that are stopped, and whose status
has not yet been reported since they stopped, is also reported to the requesting pro-
cess.
542 Hewlett-Packard Company − 1 − HP-UX 11i Version 3: February 2007