02-26-2002
Nothing that you're saying makes any sense at all.
A process has total control over when a child is created. When it invokes fork(), that is exactly when the process is created. The child exists when the very next statement is executed.
There is no need at all to synchonize the reading and writing on a pipe. The reader do can invoke read() hours before the data is written...it will simply wait unless it sets O_NDELAY in which case it returns immediately...so don't set that option. The reader can also read() hours after the write() on the other end. The data will wait. Neither case can cause a broken pipe, which is the error you complained about. That is caused by the reader exiting prior to the write.
Your real problem is that you'e trying to run a marathon when you can't yet walk.
If you attempt to use pipes in a full-duplex manner or use two pipe to achieve a two-way communication between processes, you will almost certainly cause deadlock. Get the data flowing in a single direction before you try to move on.
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PIPE(2) BSD System Calls Manual PIPE(2)
NAME
pipe -- create descriptor pair for interprocess communication
SYNOPSIS
#include <unistd.h>
int
pipe(int fildes[2]);
DESCRIPTION
The pipe() function creates a pipe (an object that allows unidirectional data flow) and allocates a pair of file descriptors. The first
descriptor connects to the read end of the pipe; the second connects to the write end.
Data written to fildes[1] appears on (i.e., can be read from) fildes[0]. This allows the output of one program to be sent to another pro-
gram: the source's standard output is set up to be the write end of the pipe; the sink's standard input is set up to be the read end of the
pipe. The pipe itself persists until all of its associated descriptors are closed.
A pipe whose read or write end has been closed is considered widowed. Writing on such a pipe causes the writing process to receive a SIGPIPE
signal. Widowing a pipe is the only way to deliver end-of-file to a reader: after the reader consumes any buffered data, reading a widowed
pipe returns a zero count.
The generation of the SIGPIPE signal can be suppressed using the F_SETNOSIGPIPE fcntl command.
RETURN VALUES
On successful creation of the pipe, zero is returned. Otherwise, a value of -1 is returned and the variable errno set to indicate the error.
ERRORS
The pipe() call will fail if:
[EFAULT] The fildes buffer is in an invalid area of the process's address space.
[EMFILE] Too many descriptors are active.
[ENFILE] The system file table is full.
SEE ALSO
sh(1), fork(2), read(2), socketpair(2), fcntl(2), write(2)
HISTORY
A pipe() function call appeared in Version 6 AT&T UNIX.
4th Berkeley Distribution February 17, 2011 4th Berkeley Distribution