123 lines
2.5 KiB
Plaintext
123 lines
2.5 KiB
Plaintext
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.TH WAIT 2
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.SH NAME
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await, wait, waitpid \- wait for a process to exit
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.B
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Waitmsg* wait(void)
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.PP
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.B
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int waitpid(void)
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.PP
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.B
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int await(char *s, int n)
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.SH DESCRIPTION
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.I Wait
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causes a process to wait for any child process (see
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.IR fork (2))
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to exit.
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It returns a
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.B Waitmsg
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holding
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information about the exited child.
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A
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.B Waitmsg
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has this structure:
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.IP
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.EX
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.ta 6n +\w'long 'u +\w'msg[ERRLEN]; 'u
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typedef
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struct Waitmsg
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{
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int pid; /* of loved one */
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ulong time[3]; /* of loved one & descendants */
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char *msg;
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} Waitmsg;
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.EE
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.PP
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.B Pid
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is the child's
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process id.
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The
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.B time
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array contains the time the child and its descendants spent in user code,
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the time spent in system calls, and the child's elapsed real time,
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all in units of milliseconds.
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.B Msg
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contains the message that the child specified in
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.IR exits (2).
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For a normal exit,
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.B msg[0]
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is zero,
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otherwise
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.B msg
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is the exit string
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prefixed by the process name, a blank, the process id, and a colon.
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.PP
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If there are no more children to wait for,
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.I wait
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returns immediately, with return value nil.
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.PP
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The
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.B Waitmsg
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structure is allocated by
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.IR malloc (2)
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and should be freed after use.
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For programs that only need the pid of the exiting program,
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.I waitpid
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returns just the pid and discards the rest of the information.
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.PP
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The underlying system call is
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.IR await ,
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which fills in the n-byte buffer
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.I s
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with a textual representation of the pid, times, and exit string.
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There is no terminal NUL.
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The return value is the length, in bytes, of the data.
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.PP
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The buffer filled in by
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.I await
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may be parsed (after appending a NUL) using
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.IR tokenize
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(see
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.IR getfields (2));
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the resulting fields are, in order, pid, the three times, and the exit string,
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which will be
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.B ''
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for normal exit.
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If the representation is longer than
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.I n
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bytes, it is truncated but, if possible, properly formatted.
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The information that does not fit in the buffer is discarded, so
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a subsequent call to
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.I await
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will return the information about the next exiting child, not the remainder
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of the truncated message.
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In other words, each call to
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.I await
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returns the information about one child, blocking if necessary if no child has exited.
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.PP
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If the calling process has no living children,
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.I await
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and
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.I waitpid
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return
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.BR -1 .
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.SH SOURCE
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.B /sys/src/libc/9syscall
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.br
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.B /sys/src/libc/9sys
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.SH "SEE ALSO"
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.IR fork (2),
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.IR exits (2),
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the
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.B wait
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file in
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.IR proc (3)
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.SH DIAGNOSTICS
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These routines set
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.IR errstr .
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