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wait(2) wait(2)

NAME

wait, waitpid - wait for child process to stop or terminate

SYNOPSIS

#include <sys/types.h> OH

#include <sys/wait.h>

pid_t wait(int *stat_loc);

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

DESCRIPTION

The wait() and waitpid() functions allow the calling process to obtain status information pertaining

to one of its child processes. Various options permit status information to be obtained for child processes

that have terminated 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 will suspend execution of the calling process until status information for one of its

terminated child processes is available, or until delivery of a signal whose action is either to execute a

signal-catching function or to terminate the process. If status information is available prior to the call to

wait(), return will be immediate.

The waitpid() function will behave identically to wait(), if the pid argument is (pid_t)−1 and the

options argument is 0. Otherwise, its behaviour will be modiﬁed by the values of the pid and options argu-

ments.

The pid argument speciﬁes a set of child processes for which status is requested. The

waitpid() func-

tion will only return 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 then 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.

• 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 options argument is constructed from the bitwise-inclusive OR of zero or more of the following ﬂags,

deﬁned in the header <sys/wait.h> .

WCONTINUED The waitpid() function will report the status of any continued child pro-

cess speciﬁed by pid whose status has not been reported since it continued

from a job control stop.

WNOHANG The waitpid() function will not suspend execution of the calling process

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, will also be

reported to the requesting process.

If the calling process has SA_NOCLDWAIT set or has SIGCHLD set to SIG_IGN, and the process has no

unwaited for children that were transformed into zombie processes, it will block until all of its children ter-

minate, and wait() and waitpid() will fail and set errno to ECHILD.

If wait() or waitpid() return because the status of a child process is available, these functions will

return a value equal to the process ID of the child process. In this case, if the value of the argument

stat_loc is not a null pointer, information will be stored in the location pointed to by stat_loc. If and only if

the status returned is from a terminated child process that returned 0 from main() or passed 0 as the

status argument to _exit() or exit(), the value stored at the location pointed to by stat_loc will be 0.

Regardless of its value, this information may be interpreted using the following macros, which are deﬁned

in <sys/wait.h> and evaluate to integral expressions; the stat_val argument is the integer value

pointed to by stat_loc.

HP-UX Release 11i: December 2000 − 1 − Section 2−−449

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