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<head>
<title>wait(3) - Plan 9 from User Space</title>
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<tr><td width=20><td>
<tr><td width=20><td><b>WAIT(3)</b><td align=right><b>WAIT(3)</b>
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<br>
<p><font size=+1><b>NAME </b></font><br>
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await, awaitnohang, awaitfor, wait, waitnohang, waitfor, waitpid
– wait for a process to exit<br>
</table>
<p><font size=+1><b>SYNOPSIS </b></font><br>
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<tt><font size=+1>#include <u.h><br>
#include <libc.h>
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</font></tt>
<tt><font size=+1>Waitmsg* wait(void)
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</font></tt>
<tt><font size=+1>Waitmsg* waitnohang(void)
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</font></tt>
<tt><font size=+1>Waitmsg* waitfor(int pid)
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</font></tt>
<tt><font size=+1>int waitpid(void)
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</font></tt>
<tt><font size=+1>int await(char *s, int n)
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</font></tt>
<tt><font size=+1>int awaitnohang(char *s, int n)
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</font></tt>
<tt><font size=+1>int awaitfor(int pid, char *s, int n)<br>
</font></tt>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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<i>Wait</i> causes a process to wait for any child process (see <a href="../man2/fork.html"><i>fork</i>(2)</a>
and <a href="../man3/rfork.html"><i>rfork</i>(3)</a>) to exit. It returns a <tt><font size=+1>Waitmsg</font></tt> holding information
about the exited child. A <tt><font size=+1>Waitmsg</font></tt> has this structure:<br>
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<tt><font size=+1>typedef<br>
struct Waitmsg<br>
{<br>
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int pid; /* of loved one */<br>
ulong time[3]; /* of loved one & descendants */<br>
char *msg;<br>
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} Waitmsg;<br>
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</font></tt>
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<tt><font size=+1>Pid</font></tt> is the child’s process id. The <tt><font size=+1>time</font></tt> array contains the time
the child and its descendants spent in user code, the time spent
in system calls, and the child’s elapsed real time, all in units
of milliseconds. <tt><font size=+1>Msg</font></tt> contains the message that the child specified
in <a href="../man3/exits.html"><i>exits</i>(3)</a>. For a normal exit, <tt><font size=+1>msg[0]</font></tt> is zero, otherwise <tt><font size=+1>msg
</font></tt>is the exit string prefixed by the process name, a blank, the
process id, and a colon.
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If there are no more children to wait for, <i>wait</i> returns immediately,
with return value nil.
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The <tt><font size=+1>Waitmsg</font></tt> structure is allocated by <a href="../man3/malloc.html"><i>malloc</i>(3)</a> and should be
freed after use. For programs that only need the pid of the exiting
program, <i>waitpid</i> returns just the pid and discards the rest of
the information.
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<i>Waitnohang</i> is like <i>wait</i> but does not block if there are no more
children to wait for. Instead it returns immediately and sets
<i>errstr</i>.
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<i>Waitfor</i> is like <i>wait</i> but waits for a particular <i>pid</i>.
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The underlying calls are <i>await</i>, <i>awaitnohang</i>, and <i>awaitfor</i>, which
fill in the <i>n</i>-byte buffer <i>s</i> with a textual representation of the
pid, times, and exit string. There is no terminal NUL. The return
value is the length, in bytes, of the data.
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The filled-in buffer may be parsed (after appending a NUL) using
<i>tokenize</i> (see <a href="../man3/getfields.html"><i>getfields</i>(3)</a>); the resulting fields are, in order,
pid, the three times, and the exit string, which will be <tt><font size=+1>''</font></tt> for
normal exit. If the representation is longer than <i>n</i> bytes, it
is truncated but, if possible, properly formatted. The information
that
does not fit in the buffer is discarded, so a subsequent call
to <i>await</i> will return the information about the next exiting child,
not the remainder of the truncated message. In other words, each
call to <i>await</i> returns the information about one child, blocking
if necessary if no child has exited. If the calling process has
no
living children, <i>await</i> returns <tt><font size=+1>−1</font></tt>.<br>
</table>
<p><font size=+1><b>SOURCE </b></font><br>
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<tt><font size=+1>/usr/local/plan9/src/lib9/wait.c
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</font></tt>
<tt><font size=+1>/usr/local/plan9/src/lib9/await.c<br>
</font></tt>
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<p><font size=+1><b>SEE ALSO </b></font><br>
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<a href="../man3/rfork.html"><i>rfork</i>(3)</a>, <a href="../man3/exits.html"><i>exits</i>(3)</a>,<br>
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<p><font size=+1><b>DIAGNOSTICS </b></font><br>
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These routines set <i>errstr</i>.<br>
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<p><font size=+1><b>BUGS </b></font><br>
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To avoid name conflicts with the underlying system, <i>wait</i>, <i>waitpid</i>,
and <i>waitfor</i> are preprocessor macros defined as <i>p9wait</i>, <i>p9waitpid</i>,
and <i>p9waitfor</i>; see <a href="../man3/intro.html"><i>intro</i>(3)</a>.<br>
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