On 10/8/2011 11:35 AM, Ken Brown wrote:
The attached STC arose from my attempt to understand the problem
discussed starting in
http://cygwin.com/ml/cygwin/2011-09/msg00405.html .
I'm starting a new thread because there appears to be a Cygwin problem
having nothing to do with emacs.
The STC creates a pipe and then runs `bash -ic ls' in a subprocess, with
both stdout and stderr sent to the pipe. The parent process reads from
the pipe and echoes it to the terminal.
On Linux, I first get the error messages (presumably expected)
bash: cannot set terminal process group (-1): Invalid argument
bash: no job control in this shell
followed by the directory listing. On Cygwin, the bash process produces
no output but is simply stopped, and I have to kill it from another
terminal before the main program will exit. This happens both with
cygwin-1.7.9 and the latest snapshot. Here are a few comments:
1. The problem disappears if I don't send bash's stderr to the pipe.
2. The problem also disappears if I replace -ic by -c in the call to
bash, presumably because there's nothing sent to stderr in that case.
3. The problem disappears if I don't use a pipe but just have the bash
subprocess write to the terminal, even if I redirect bash's stderr to
stdout.
Attached is a slight modification of the STC, in which I set stdin for
the bash subprocess to /dev/null. With this modification, the program
works as expected (and as on Linux) with cygwin-1.7.9, but the same
problem as before occurs with the latest snapshot.
Ken
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
int
main()
{
char *argv[4];
char buf;
int fd[2];
int nullfd = open ("/dev/null", O_RDONLY);
pid_t pid;
argv[0] = "bash";
argv[1] = "-ic";
argv[2] = "ls";
argv[3] = '\0';
pipe (fd);
pid = fork();
if (pid == 0)
{
setsid ();
close (0);
close (1);
close (2);
dup2 (nullfd, 0);
dup2 (fd[1], 1);
dup2 (fd[1], 2);
close (fd[1]);
close (nullfd);
execvp (argv[0], argv);
}
close (fd[1]);
close (nullfd);
while (read (fd[0], &buf, 1) > 0)
write (1, &buf, 1);
close (fd[0]);
}
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
