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X-Authentication-Warning: vivaldi.cpe.ku.ac.th: ans owned process doing -bs
Date: Mon, 22 Jan 2001 00:10:58 +0700 (ICT)
From: Anon Sricharoenchai <ans AT beethoven DOT cpe DOT ku DOT ac DOT th>
X-Sender: ans AT vivaldi DOT cpe DOT ku DOT ac DOT th
To: cygwin AT cygwin DOT com
Subject: Bug when reading from a non-blocking pipe file descriptor, while
 the opposite end (the writing pipe file descriptor) is closed.
Message-ID: <Pine.LNX.4.21.0101212338330.27606-100000@vivaldi.cpe.ku.ac.th>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII


The following is the C program to regenerate this bug.


#include <unistd.h>
#include <sys/time.h>
#include <sys/types.h>
#include <fcntl.h>
#include <stdio.h>

void test_func(int n1, int n2) {
   int input_from_child[2];
   pipe(input_from_child);
   if (fork()) {
      char buf[20];
      close(input_from_child[1]);
      fcntl(input_from_child[0], F_SETFL, O_NONBLOCK);
      sleep(n1);
      printf("%d\n", read(input_from_child[0], buf, sizeof(buf)));
   } else {
      close(input_from_child[0]);
      dup2(input_from_child[1], 1);
      close(input_from_child[1]);
      sleep(n2);
      exit(0);
   };
};

int main() {
   test_func(1, 0);
   test_func(1, 2);
   return 0;
};


When compile and run on linux, the output of running this program should
be as follow.

0
-1

But when compile and run using cygwin, the output will be as follow.

-1
-1

The latter case is a bug on cygwin.  Because when calling 
read(input_from_child[0], buf, sizeof(buf)) from test_func(1, 0), the
file descriptor input_from_child[0] should be in the end of file status
that should cause the read(...) to return 0.


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