await, awaitnohang, awaitfor, wait, waitnohang, waitfor, waitpid
– wait for a process to exit|
Waitmsg* waitfor(int pid)
int await(char *s, int n)
int awaitnohang(char *s, int n)
int awaitfor(int pid, char *s, int n)
Wait causes a process to wait for any child process (see fork(2)
and rfork(3)) to exit. It returns a Waitmsg holding information
about the exited child. A Waitmsg has this structure:|
Pid is the child’s process id. The time 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. Msg contains the message that the child specified
in exits(3). For a normal exit, msg is zero, otherwise msg
is the exit string prefixed by the
process name, a blank, the process id, and a colon.
If there are no more children to wait for, wait returns immediately,
with return value nil.
The Waitmsg structure is allocated by malloc(3) and should be
freed after use. For programs that only need the pid of the exiting
program, waitpid returns just the pid and discards the rest of
Waitnohang is like wait but does not block if there are no more
children to wait for. Instead it returns immediately and sets
Waitfor is like wait but waits for a particular pid.
The underlying calls are await, awaitnohang, and awaitfor, which
fill in the n-byte buffer s 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.
The filled-in buffer may be parsed (after appending a NUL) using
tokenize (see getfields(3)); the resulting fields are, in order,
pid, the three times, and the exit string, which will be '' for
normal exit. If the representation is longer than n 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 await will return the information about the
next exiting child, not the remainder of the truncated message.
In other words, each call to await returns the information about
one child, blocking if necessary if no child has exited. If the
calling process has no living children, await returns −1.
int pid; /* of loved one */|
ulong time; /* of loved one & descendants */
These routines set errstr.|
To avoid name conflicts with the underlying system, wait, waitpid,
and waitfor are preprocessor macros defined as p9wait, p9waitpid,
and p9waitfor; see intro(3).|