2.11BSD/man/cat2/wait3.0
WAIT(2) UNIX Programmer's Manual WAIT(2)
NAME
wait, waitpid, wait4, wait3 - wait for process terminatation
SYNOPSIS
#include <sys/types.h>
#include <sys/wait.h>
pid = wait(status)
int pid;
union wait *status;
#include <sys/time.h>
#include <sys/resource.h>
pid = waitpid(wpid, status, options);
int pid;
int wpid;
union wait *status;
int options;
pid = wait3(status, options, rusage);
int pid;
union wait *status;
int options;
struct rusage *rusage;
pid = wait4(wpid, status, options, rusage);
int pid;
int wpid;
union wait *status;
int options;
struct rusage *rusage;
DESCRIPTION
The _w_a_i_t function suspends execution of its calling process
until status information is available for a terminated child
process, or a signal is received. On return from a success-
ful _w_a_i_t call, the status area contains termination informa-
tion about the process that exited as defined below.
The _w_a_i_t_4 call provides a more general interface for pro-
grams that need to wait for certain child processes, that
need resource utilization statistics accummulated by child
processes, or that require options. The other wait func-
tions are implemented using _w_a_i_t_4 .
The wpid parameter specifies the set of child processes for
which to wait. If wpid is -1, the call waits for any child
process. If wpid is 0, the call waits for any child process
in the process group of the caller. If wpid is greater than
zero, the call waits for the process with process id wpid .
If wpid is less than -1, the call waits for any process
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whose process group id equals the absolute value of wpid .
The status parameter is defined below. The options parame-
ter contains the bitwise OR of any of the following options.
The WNOHANG option is used to indicate that the call should
not block if there are no processes that wish to report
status. If the WUNTRACED option is set, children of the
current process that are stopped due to a SIGTTIN , SIGTTOU
, SIGTSTP , or SIGSTOP signal also have their status
reported.
If rusage is non-zero, 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 wish
to report status, _w_a_i_t_4 returns a process id of 0.
The _w_a_i_t_p_i_d call is identical to _w_a_i_t_4 with an rusage value
of zero. The older _w_a_i_t_3 call is the same as _w_a_i_t_4 with a
wpid value of -1.
The following macros may be used to test the manner of exit
of the process. One of the first three macros will evaluate
to a non-zero (true) value:
_W_I_F_E_X_I_T_E_D(_s_t_a_t_u_s) - True if the process terminated normally
by a call to __e_x_i_t(_2) or _e_x_i_t(_2) .
_W_I_F_S_I_G_N_A_L_E_D(_s_t_a_t_u_s) - True if the process terminated due to
receipt of a signal.
_W_I_F_S_T_O_P_P_E_D(_s_t_a_t_u_s) - True if the process has not terminated,
but has stopped and can be restarted. This macro can be
true only if the wait call specified the WUNTRACED option or
if the child process is being traced (see _p_t_r_a_c_e(_2)).
Depending on the values of those macros, the following mac-
ros produce the remaining status information about the child
process:
_W_E_X_I_T_S_T_A_T_U_S(_s_t_a_t_u_s) - If _W_I_F_E_X_I_T_E_D(_s_t_a_t_u_s) is true, evalu-
ates to the low-order 8 bits of the argument passed to
__e_x_i_t(_2) or _e_x_i_t(_2) by the child.
_W_T_E_R_M_S_I_G(_s_t_a_t_u_s) - If _W_I_F_S_I_G_N_A_L_E_D(_s_t_a_t_u_s) is true, evaluates
to the number of the signal that caused the termination of
the process.
_W_C_O_R_E_D_U_M_P(_s_t_a_t_u_s) If _W_I_F_S_I_G_N_A_L_E_D(_s_t_a_t_u_s) is true, evaluates
as true if the termination of the process was accompanied by
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the creation of a core file containing an image of the pro-
cess when the signal was received.
_W_S_T_O_P_S_I_G(_s_t_a_t_u_s) If _W_I_F_S_T_O_P_P_E_D(_s_t_a_t_u_s) is true, evaluates to
the number of the signal that caused the process to stop.
NOTES
See _s_i_g_v_e_c(_2) for a list of termination signals. A status
of 0 indicates normal termination.
If a parent process terminates without waiting for all of
its child processes to terminate, the remaining child
processes are assigned the parent process 1 ID (the init
process ID).
If a signal is caught while any of the _w_a_i_t calls is pend-
ing, the call may be interrupted or restarted when the
signal-catching routine returns, depending on the options in
effect for the signal; see _i_n_t_r_o(_2), System call restart.
RETURN VALUES
If _w_a_i_t() returns due to a stopped or terminated child pro-
cess, the process ID of the child is returned to the calling
process. Otherwise, a value of -1 is returned and _e_r_r_n_o is
set to indicate the error.
If _w_a_i_t_4(), _w_a_i_t_3() _o_r _w_a_i_t_p_i_d() returns due to a stopped or
terminated child process, the process ID of the child is
returned to the calling process. If there are no children
not previously awaited, -1 is returned with _e_r_r_n_o set to
[ECHILD]. Otherwise, if WNOHANG is specified and there are
no stopped or exited children, 0 is returned. If an error
is detected or a caught signal aborts the call, a value of
-1 is returned and _e_r_r_n_o is set to indicate the error.
ERRORS
_W_a_i_t() will fail and return immediately if:
[ECHILD] The calling process has no existing
unwaited-for child processes.
[EFAULT] The _s_t_a_t_u_s or _r_u_s_a_g_e arguments point to an
illegal address. (May not be detected before
exit of a child process.)
[EINTR] The call was interrupted by a caught signal,
or the signal had the _S_V__I_N_T_E_R_R_U_P_T flag set.
STANDARDS
The _w_a_i_t and _w_a_i_t_p_i_d functions are defined by POSIX; _w_a_i_t_4
and _w_a_i_t_3 are not specified by POSIX. The _W_C_O_R_E_D_U_M_P macro
and the ability to restart a pending _w_a_i_t call are
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extensions to the POSIX interface.
SEE ALSO
_e_x_i_t(_2) , _s_i_g_v_e_c(_2) A _w_a_i_t function call appeared in Version
6 AT&T UNIX.
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