WAIT(2)WAIT(2)NAME
wait, wait3, wait4, WIFSTOPPED, WIFSIGNALED, WIFEXITED - wait for
process to terminate or stop (BSD version)
SYNOPSIS
#include <sys/wait.h>
int wait(statusp)
union wait ∗statusp;
int wait((union wait ∗)0)
#include <sys/time.h>
#include <sys/resource.h>
int wait3(statusp, options, rusage)
union wait ∗statusp;
int options;
struct rusage ∗rusage;
int wait4(pid, statusp, options, rusage)
int pid;
union wait ∗statusp;
int options;
struct rusage ∗rusage;
WIFSTOPPED(status)
union wait status;
WIFSIGNALED(status)
union wait status;
WIFEXITED(status)
union wait status;
DESCRIPTION
This is the BSD specification for wait. For the POSIX specification,
see wait(2P).
wait() delays its caller until a signal is received or one of its child
processes terminates or stops due to tracing. If any child has died or
stopped due to tracing and this has not been reported using wait,
return is immediate, returning the process ID and exit status of one of
those children. If that child had died, it is discarded. If there are
no children, return is immediate with the value -1 returned. If there
are only running or stopped but reported children, the calling process
is blocked.
If status is not a NULL pointer, then on return from a successful
wait() call the status of the child process whose process ID is the
return value of wait() is stored in the wait() union pointed to by
status. The w_status member of that union is an int; it indicates the
cause of termination and other information about the terminated process
in the following manner:
- If the low-order 8 bits of w_status are equal to 0177, the
child process has stopped; see ptrace(2) and sigvec(2).
- If the low-order 8 bits of w_status are non-zero and are
not equal to 0177, the child process terminated due to a
signal; the low-order 7 bits of w_status contain the number
of the signal that terminated the process. In addition, if
the low-order seventh bit of w_status (that is, bit 0200)
is set, a ``core image'' of the process was produced; see
sigvec(2).
- Otherwise, the child process terminated due to an exit()
call; the 8 bits higher up from the low-order 8 bits of
w_status contain the low-order 8 bits of the argument that
the child process passed to exit; see exit(2).
Other members of the wait() union can be used to extract this
information more conveniently:
- If the w_stopval member has the value WSTOPPED, the child
process has stopped; the value of the w_stopsig member is
the signal that stopped the process.
- If the w_termsig member is non-zero, the child process
terminated due to a signal; the value of the w_termsig
member is the number of the signal that terminated the
process. If the w_coredump member is non-zero, a core dump
was produced.
- Otherwise, the child process terminated due to an exit()
call; the value of the w_retcode member is the low-order 8
bits of the argument that the child process passed to exit.
The other members of the wait() union merely provide an alternate way
of analyzing the status. The value stored in the w_status field is
compatible with the values stored by other versions of the UNIX system,
and an argument of type int ∗ may be provided instead of an argument of
type union wait ∗ for compatibility with those versions.
wait3() is an alternate interface that allows both non-blocking status
collection and the collection of the status of children stopped by any
means. The status parameter is defined as above. The options
parameter is used to indicate the call should not block if there are no
processes that have status to report (WNOHANG), and/or that children of
the current process that are stopped due to a SIGTTIN, SIGTTOU,
SIGTSTP, or SIGSTOP signal are eligible to have their status reported
as well (WUNTRACED). A terminated child is discarded after it reports
status, and a stopped process will not report its status more than
once. If rusage is not a NULL pointer, a summary of the resources used
by the terminated process and all its children is returned. (This
information is currently not available for stopped processes.)
When the WNOHANG option is specified and no processes have status to
report, wait3() returns 0. The WNOHANG and WUNTRACED options may be
combined by ORing the two values.
wait4() is another alternate interface. With a pid argument of 0, it
is equivalent to wait3. If pid has a nonzero value, then wait4()
returns status only for the indicated process ID, but not for any other
child processes.
WIFSTOPPED, WIFSIGNALED, WIFEXITED, are macros that take an argument
status, of type `union wait', as returned by wait, wait2, wait3, or
wait4. WIFSTOPPED evaluates to true (1) when the process for which the
wait() call was made is stopped, or to false (0) otherwise.
WIFSIGNALED evaluates to true when the process was terminated with a
signal. WIFEXITED evaluates to true when the process exited by using
an exit(2) call.
NOTES
If a parent process terminates without waiting on its children, the
initialization process (process ID = 1) inherits the children.
wait, wait3, and wait4() are automatically restarted when a process
receives a signal while awaiting termination of a child process, unless
the SV_INTERRUPT bit is set in the flags for that signal.
RETURN VALUE
If wait() returns due to a stopped or terminated child process, the
process ID of the child is returned to the calling process. Otherwise,
a value of -1 is returned and errno is set to indicate the error.
wait3() and wait4() return 0 if WNOHANG is specified and there are no
stopped or exited children, and return the process ID of the child
process if they return due to a stopped or terminated child process.
Otherwise, they return a value of -1 and set errno to indicate the
error.
ERRORS
wait, wait3, or wait4 will fail and return immediately if one or more
of the following are true:
ECHILD The calling process has no existing unwaited-for
child processes.
EFAULT The status or rusage arguments point to an illegal
address.
wait, wait3, and wait4 will terminate prematurely, return -1, and set
errno to EINTR upon the arrival of a signal whose SV_INTERRUPT bit in
its flags field is set (see sigvec(2) and siginterrupt(3)).
SEE ALSOexit(2), getrusage(2), sigvec(2), siginterrupt(3), signal(3), wait(2P)WARNINGS
Calls to wait with an argument of 0 should be cast to type
`unionwait*', as in:
wait( (union wait *) 0)
Otherwise the compiler might complain.
27 May 1988 WAIT(2)
