подождите, пока дочерний процесс остановится или завершится (wait for a child process to stop or terminate)
Имя (Name)
wait, waitpid — wait for a child process to stop or terminate
Синопсис (Synopsis)
#include <sys/wait.h>
pid_t wait(int *stat_loc);
pid_t waitpid(pid_t pid, int *stat_loc, int options);
Описание (Description)
The wait() and waitpid() functions shall obtain status
information (see Section 2.13, Status Information) pertaining to
one of the caller's child processes. The wait() function obtains
status information for process termination from any child
process. The waitpid() function obtains status information for
process termination, and optionally process stop and/or continue,
from a specified subset of the child processes.
The wait() function shall cause the calling thread to become
blocked until status information generated by child process
termination is made available to the thread, or until delivery of
a signal whose action is either to execute a signal-catching
function or to terminate the process, or an error occurs. If
termination status information is available prior to the call to
wait(), return shall be immediate. If termination status
information is available for two or more child processes, the
order in which their status is reported is unspecified.
As described in Section 2.13, Status Information, the wait() and
waitpid() functions consume the status information they obtain.
The behavior when multiple threads are blocked in wait(),
waitid(), or waitpid() is described in Section 2.13, Status
Information.
The waitpid() function shall be equivalent to wait() if the pid
argument is (pid_t)-1 and the options argument is 0. Otherwise,
its behavior shall be modified by the values of the pid and
options arguments.
The pid argument specifies a set of child processes for which
status is requested. The waitpid() function shall 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
<sys/wait.h> header:
WCONTINUED The waitpid() function shall report 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 shall 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, shall also be reported
to the requesting process.
If wait() or waitpid() return because the status of a child
process is available, these functions shall 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
shall be stored in the location pointed to by stat_loc. The
value stored at the location pointed to by stat_loc shall be 0 if
and only if the status returned is from a terminated child
process that terminated by one of the following means:
1. The process returned 0 from main().
2. The process called _exit() or exit() with a status argument
of 0.
3. The process was terminated because the last thread in the
process terminated.
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.
WIFEXITED(stat_val)
Evaluates to a non-zero value if status was returned for a
child process that terminated normally.
WEXITSTATUS(stat_val)
If the value of WIFEXITED(stat_val) 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 the
value the child process returned from main().
WIFSIGNALED(stat_val)
Evaluates to a non-zero value if status was returned for a
child process that terminated due to the receipt of a
signal that was not caught (see <signal.h>).
WTERMSIG(stat_val)
If the value of WIFSIGNALED(stat_val) is non-zero, this
macro evaluates to the number of the signal that caused the
termination of the child process.
WIFSTOPPED(stat_val)
Evaluates to a non-zero value if status was returned for a
child process that is currently stopped.
WSTOPSIG(stat_val)
If the value of WIFSTOPPED(stat_val) is non-zero, this
macro evaluates to the number of the signal that caused the
child process to stop.
WIFCONTINUED(stat_val)
Evaluates to a non-zero value if status was returned for a
child process that has continued from a job control stop.
It is unspecified whether the status value returned by calls to
wait() or waitpid() for processes created by posix_spawn() or
posix_spawnp() can indicate a WIFSTOPPED(stat_val) before
subsequent calls to wait() or waitpid() indicate
WIFEXITED(stat_val) as the result of an error detected before the
new process image starts executing.
It is unspecified whether the status value returned by calls to
wait() or waitpid() for processes created by posix_spawn() or
posix_spawnp() can indicate a WIFSIGNALED(stat_val) if a signal
is sent to the parent's process group after posix_spawn() or
posix_spawnp() is called.
If the information pointed to by stat_loc was stored by a call to
waitpid() that specified the WUNTRACED flag and did not specify
the WCONTINUED flag, exactly one of the macros
WIFEXITED(*stat_loc), WIFSIGNALED(*stat_loc), and
WIFSTOPPED(*stat_loc) shall evaluate to a non-zero value.
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 WIFEXITED(*stat_loc),
WIFSIGNALED(*stat_loc), WIFSTOPPED(*stat_loc), and
WIFCONTINUED(*stat_loc) shall evaluate to a non-zero value.
If the information pointed to by stat_loc was stored by a call to
waitpid() that did not specify the WUNTRACED or WCONTINUED flags,
or by a call to the wait() function, exactly one of the macros
WIFEXITED(*stat_loc) and WIFSIGNALED(*stat_loc) shall evaluate to
a non-zero value.
If the information pointed to by stat_loc was stored by a call to
waitpid() that did not specify the WUNTRACED flag and specified
the WCONTINUED flag, exactly one of the macros
WIFEXITED(*stat_loc), WIFSIGNALED(*stat_loc), and
WIFCONTINUED(*stat_loc) shall evaluate to a non-zero value.
If _POSIX_REALTIME_SIGNALS is defined, and the implementation
queues the SIGCHLD signal, then if wait() or waitpid() returns
because the status of a child process is available, any pending
SIGCHLD signal associated with the process ID of the child
process shall be discarded. Any other pending SIGCHLD signals
shall remain pending.
Otherwise, if SIGCHLD is blocked, if wait() or waitpid() return
because the status of a child process is available, any pending
SIGCHLD signal shall be cleared unless the status of another
child process is available.
For all other conditions, it is unspecified whether child status
will be available when a SIGCHLD signal is delivered.
There may be additional implementation-defined circumstances
under which wait() or waitpid() report status. This shall not
occur unless the calling process or one of its child processes
explicitly makes use of a non-standard extension. In these cases
the interpretation of the reported status is implementation-
defined.
If a parent process terminates without waiting for all of its
child processes to terminate, the remaining child processes shall
be assigned a new parent process ID corresponding to an
implementation-defined system process.
