wait.2 (2010 09)

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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,

wait-

pid() 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.

• 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

waitable 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 request-

ing process.

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (4 pages)

PAGE 1
wait(2) wait(2) NAME wait(), waitpid() - wait for child process to stop or terminate SYNOPSIS #include #include 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 terminated or stopped.
PAGE 2
wait(2) wait(2) HP-UX EXTENSION: If and only if this flag is set, waitpid() or wait3() (see wait3 (2)) returns information on child or attached processes that are stopped because they received a SIGTTIN, SIGTTOU, SIGTSTP or SIGSTOP signal, and whose status has not yet been reported. Regardless of this flag, status is returned for child or attached processes that have terminated or are stopped and traced and whose status has not yet been reported.
PAGE 3
wait(2) wait(2) If the information pointed to by stat_loc was stored by a call to waitpid() that specified the WUNTRACED and WCONTINUED flags, exactly one of the macros WIFCONTINUED(*stat_loc), WIFEXITED(*stat_loc ), WIFSIGNALED(*stat_loc ), and WIFSTOPPED(*stat_loc ) evaluates to a nonzero value.
PAGE 4
wait(2) wait(2) WARNINGS HP-UX EXTENSION: The operation of wait(), waitpid() is affected if the SIGCLD signal is set to SIG_IGN (see the WARNINGS section of signal (5)). Signal handlers that cause system calls to be restarted can affect the [EINTR] condition (see bsdproc (3C) and sigaction (2)). APPLICATION USAGE Threads Considerations In a multithreaded application, only the calling thread is suspended by wait(), waitpid() call.