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Annotated edit history of wait4(2) version 2, including all changes. View license author blame.
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1 perry 1 !!NAME
2 PerryLorier 2 wait4 - wait for process termination, BSD style
1 perry 3 !!SYNOPSIS
2 PerryLorier 4 #include <sys/types.h>
5 #include <sys/time.h>
6 #include <sys/resource.h>
7 #include <sys/wait.h>
8 __pid_t wait4(pid_t__ ''pid''__, int *__''status''__, int__ ''options''__, struct rusage *__''rusage''__)__
1 perry 9 !!DESCRIPTION
2 PerryLorier 10 The __wait4__ function suspends execution of the current process until a child as specified by the ''pid'' argument has exited, or until a signal is delivered whose action is to terminate the current process or to call a signal handling function. If a child as requested by ''pid'' has already exited by the time of the call (a so-called "zombie" process), the function returns immediately. Any system resources used by the child are freed.
1 perry 11
12 The value of ''pid'' can be one of:
2 PerryLorier 13 ;<-1:which means to wait for any child process whose process group ID is equal to the absolute value of ''pid''.
14 ;-1:which means to wait for any child process; this is equivalent to calling wait3(2).
15 ;0:which means to wait for any child process whose process group ID is equal to that of the calling process.
16 ;>0:which means to wait for the child whose process ID is equal to the value of ''pid''.
1 perry 17
2 PerryLorier 18 The value of ''options'' is a bitwise OR of zero or more of the following constants:
19 ;__WNOHANG__: which means to return immediately if no child is there to be waited for.
20 ;__WUNTRACED__: which means to also return for children which are stopped, and whose status has not been reported.
1 perry 21
2 PerryLorier 22 If ''status'' is not __NULL__, __wait3__ or __wait4__ store status information in the location pointed to by ''status''.
1 perry 23
2 PerryLorier 24 This status can be evaluated with the following macros (these macros take the stat buffer (an __int__) as an argument -- not a pointer to the buffer!):
1 perry 25
2 PerryLorier 26 ;__WIFEXITED(__''status''__)__; is non-zero if the child exited normally.
27 ;__WEXITSTATUS(__''status''__)__: evaluates to the least significant eight bits of the return code of the child which terminated, which may have been set as the argument to a call to exit(3) or as the argument for a __return__ statement in the main program. This macro can only be evaluated if __WIFEXITED__ returned non-zero.
28 ;__WIFSIGNALED(__''status''__)__: returns true if the child process exited because of a signal which was not caught.
29 ;__WTERMSIG(__''status''__)__: returns the number of the signal that caused the child process to terminate. This macro can only be evaluated if
1 perry 30 __WIFSIGNALED__ returned non-zero.
2 PerryLorier 31 ;__WIFSTOPPED(__''status''__)__: returns true if the child process which caused the return is currently stopped; this is only possible if the call was
1 perry 32 done using __WUNTRACED__.
2 PerryLorier 33 ;__WSTOPSIG(__''status''__)__:returns the number of the signal which caused the child to stop. This macro can only be evaluated if __WIFSTOPPED__
1 perry 34 returned non-zero.
35
2 PerryLorier 36 If ''rusage'' is not __NULL__, the __struct rusage__ as defined in ''<sys/resource.h>'' it points to will be filled with accounting information. See
1 perry 37 getrusage(2) for details.
2 PerryLorier 38
1 perry 39 !!RETURN VALUE
2 PerryLorier 40 The process ID of the child which exited, -1 on error (in particular, when no unwaited-for child processes of the specified kind exist) or zero if __WNOHANG__ was used and no child was available yet. In the latter two cases ''errno'' will be set appropriately.
1 perry 41
42 !!ERRORS
2 PerryLorier 43 ;[ECHILD]: No unwaited-for child process as specified does exist.
44 ;[ERESTARTSYS]: if __WNOHANG__ was not set and an unblocked signal or a [SIGCHLD] was caught. This error is returned by the system call. The library interface is not allowed to return [ERESTARTSYS], but will return [EINTR].
1 perry 45
46 !!NOTE
2 PerryLorier 47 Including ''<sys/time.h>'' is not required these days, but increases portability. (Indeed, ''<sys/resource.h>'' defines the ''rusage'' structure with fields of type ''struct timeval'' defined in ''<sys/time.h>''.)
1 perry 48 !!CONFORMING TO
2 PerryLorier 49 SVr4, POSIX.1
1 perry 50
51 !!SEE ALSO
2 PerryLorier 52 signal(2), getrusage(2), wait(2), signal(7)
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