peter@stca77.stc.oz (Peter Jeremy) (07/07/88)
I am running SCO Xenix Release 2.2.1. I recently noticed that under some
circumstances fork() would return -1 to both parent and child, along with
errno=24 (Too many open files). Naturally, this was rather upsetting to
the processes concerned. At the time, the process had about 5 open files.
According to my understanding of fork(), that error is impossible anyway.
In addition, the process names reported by PS would randomly change to
the names of other processes. (Like having ps report 2 or 3 "init"s running
simultaneously).
Other than these problems, the system seemed to work normally. Examination
of the configuration variables didn't reveal anything overly wrong and the
system didn't complain at all.
I eventually gave up and started from fresh /usr/sys/conf/{master,xenixconf}
files. This seems to have cured the problem. Has anyone else had similar
experiences?
--
Peter Jeremy (VK2PJ) peter%stca77@stcns3.stc.oz
Alcatel-STC Australia ...!munnari!stcns3.stc.oz!stca77!peter
41 Mandible St peter%stca77@stcns3.stc.oz@uunet.UU.NET
ALEXANDRIA NSW 2015aviz@oahu.cs.ucla.edu (03/06/89)
What are the syntaxes for fork() and pipe()? I am trying to write a C program that sets up a set of child processes.. Thanks in advance...
gwyn@smoke.BRL.MIL (Doug Gwyn ) (03/06/89)
In article <21327@shemp.CS.UCLA.EDU> aviz@CS.UCLA.EDU (Dr Algirdas Avizienis) writes: >What are the syntaxes for fork() and pipe()? >I am trying to write a C program that sets up a set of child >processes.. Excuse me for saying this, but if you have to ask the net for this information because you don't have a reference manual, you'll have SERIOUS problems getting your code right. By far the preferable way to answer such questions is to refer to the UNIX Programmer's Reference Manual.
byrum@cs.odu.edu (Terry Franklin Byrum) (03/07/89)
I am borrowing this account; see signature below.
Although the obvious solution is to refer to the relevant man pages, I will
concede that there are a few commands (especially in SYSV) for which the
novice can stare at the man pages a long time and still say, "That's nice,
but HOW DO YOU USE IT??". I would include fork() and pipe() among these.
Below, I present the nucleus of a program which uses fork() and pipe().
This program is intended to highlight fork() and pipe(), so error checking is
not rigorous, and signals and abnormal child exit()s are not considered.
For a pipe to work properly, each process should close() the end of the pipe
that it does not intend to use (the reader should close the writing end,
and vice-versa). For example, if the reader does not close the writing end,
it will never perceive EOF from the pipe, since the operating system knows
that there is one potential writer (the reading process itself) still active.
An additional word to the wise: any buffering of I/O, especially by a
writing process, will drive you crazy in interprocess communication.
The reading process cannot perceive anything until it is flushed out to the
operating system. If I/O is to a terminal device, output is line-buffered
by default, which is usually acceptable. But pipes are not terminals, so
full buffering is the default, and nothing gets to the OS or the reader
until 512 (or whatever) characters have been written; rarely acceptable.
If only low level calls (read, write) are used, there is no problem.
However, if you want high level calls (fprintf, putc, puts), it is well
either to do an fflush(stream) after every batch of output, or do a
setbuf(stream, (char *)0) at the start to render the stream fully unbuffered.
Lloyd Kremer
Brooks Financial Systems
...!xanth!brooks!lloyd
Have terminal ... will hack!
-------------------cut here----------------------------------------------
/*
* A sample program to demonstrate the basic syntax of fork() and pipe()
* commands. The parent process simply writes a string through a pipe
* to be received by a child process (octal dump)
*/
main()
{
extern void perror();
int pfd[2]; /* this will be an array of 2 pipe file descriptors */
if(pipe(pfd) == -1){ /* pfd[0] is read end; pfd[1] is write end */
perror("cannot create pipe");
return(1);
}
if(!fork()){
/* CHILD STARTS HERE (fork() returns 0) */
close(pfd[1]); /* child closes write end of pipe */
close(0); /* child closes its inherited stdin descriptor */
dup(pfd[0]); /* replace it with a dup() of read end of pipe */
close(pfd[0]); /* then close original read end of pipe */
execl("/bin/od", "od", "-c", (char *)0); /* child becomes "od -c" */
perror("/bin/od"); /* if we still exist here, something's wrong */
return(1);
}
/* PARENT CONTINUES HERE (fork() returns child's pid) */
close(pfd[0]); /* parent closes read end of pipe */
write(pfd[1], "The quick brown fox jumps over the lazy dog.", 44);
/* parent says what it has to say into write end of pipe */
close(pfd[1]); /* and closes it; child will read EOF on stdin and die */
wait((int *)0); /* parent awaits death of child; avoids zombie process */
return(0);
}
-------------------cut here----------------------------------------------
--
Inventions have long since reached their limit --
and I see no hope for further developments.
- Julius Frontinus, world famous engineer, Rome, 10 AD
| Terry Franklin (Frank) Byrum
| BROOKS Financial Systems, Inc.
___ | INET: byrum@cs.odu.edu
/__ _. __. _ _ /_ | UUCP: ...!sun!xanth!brooks!byrum
/ _/ \_(_/|_|\|_/ \ | DISCLAIMER: No one listens anyway! ram@lcuxlm.ATT.COM (Miani Rich) (03/09/89)
In article <21327@shemp.CS.UCLA.EDU>, aviz@oahu.cs.ucla.edu writes: > What are the syntaxes for fork() and pipe()? > RTFM.
Pabbisetty.henr@xerox.com (Nagesh Pabbisetty) (03/13/89)
> sockets would replace the pipe, not fork and exec
Sorry about the wrong phrasing of the question. I want to know the pros and
cons of using pipes over sockets for interprocess communication.
Thanks to jvc!jonathan@uunet.UU.NET and wen-king@csvax.caltech.edu for
setting me straight.
Nagesh
716-427-1827 / 5458