waitpid() -- wait for process termination

SYNOPSIS

#include <sys/types.h>

#include <sys/wait.h>

pid_t waitpid(pid_t pid, int *stat_loc, int options);

The waitpid() function lets the calling process obtain status information about one of its child processes. If status information is available for two or more child processes, the order in which their status is reported is unspecified. If more than one thread is suspended in waitpid() awaiting termination of the same process, exactly one thread returns the process status at the time of the target child process termination. The other threads return -1, with errno set to ECHILD.

If the calling process sets SIGCHLD to SIG_IGN, and the process has no unwaited for children that were transformed into zombie processes, the calling thread blocks until all of the children of the process terminate, at which time waitpid() returns -1 with errno set to ECHILD.

If the parent process terminates without waiting for all of its child processes to terminate, the remaining child processes are assigned a new parent process ID corresponding to a system-level process.

PARAMETERS

pid

Specifies a set of child processes for which the status is requested:

If pid is equal to -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 calling process. This setting is not currently supported.

If pid is less than -1, status is requested for any child process whose process group ID is equal to the absolute value of pid. This setting is not currently supported.

stat_loc

Specifies the location to which the child process' exit status is stored. If NULL is passed, no exit status is returned. Otherwise, the following macros defined in <sys/wait.h> can be used to evaluate the returned status:

WIFEXITED(s): Evaluates to a non-zero value if status was returned for a child process that exited normally.
WEXITSTATUS(s): If the value of WIFEXITED(s) is non-zero, this macro evaluates to the low-order 8 bits of the status argument that the child process passed to exit() or _exit(), or to the value that the child process returned from main().
WIFSIGNALED(s): Evaluates to a non-zero value if status was returned for a child process that terminated due to receipt of a signal that was not caught.
WTERMSIG(s): If the value of WIFSIGNALED(s) is non-zero, this macro evaluates to the number of the signal that caused the termination of the child process.
WIFCORED(s): Evaluates to a non-zero value if status was returned for a child process that terminated due to receipt of a signal that was not caught, and whose default action is to dump core.
WCOREDUMP(s): Evaluates to a non-zero value if status was returned for a child process that terminated due to receipt of a signal that was not caught, and whose default action is to dump core.
WCORESIG(s): If the value of WIFCORED(s) is non-zero, this macro evaluates to the number of the signal that caused the termination of the child process.
WIFSTOPPED(s): Evaluates to a non-zero value if status was returned for a child process that is currently stopped.
WSTOPSIG(s): If the value of WIFSTOPPED(s) is non-zero, this macro evaluates to the number of the signal that caused the child process to stop.

options

Is the bitwise inclusive-OR of zero or more of the following flags, defined in <sys/wait.h>:

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.
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 thread. This value is currently not supported, and is ignored.

RETURN VALUES

If waitpid() was invoked with WNOHANG set in options, and there are children specified by pid for which status is not available, waitpid() returns 0. If WNOHANG was not set, waitpid() returns the process ID of a child when the status of that child is available. Otherwise, it returns -1 and sets errno to one of the following values:

ECHILD: The process or process group specified by pid does not exist or is not a child of the calling process.
EFAULT: stat_loc is not a writable address.
EINTR: The function was interrupted by a signal. The value of the location pointed to by stat_loc is undefined.
EINVAL: The options argument is not valid.
ENOSYS: pid specifies a process group (0 or less than -1), which is not currently supported.

waitpid()
wait for process termination

Function

SYNOPSIS

DESCRIPTION

PARAMETERS

RETURN VALUES

CONFORMANCE

MULTITHREAD SAFETY LEVEL

PORTING ISSUES

AVAILABILITY

SEE ALSO

waitpid() wait for process termination

Function

waitpid()
wait for process termination