Message-ID: <45903C5C.2030904@scytek.de>
Date: Mon, 25 Dec 2006 16:02:20 -0500
From: Volker Quetschke <quetschke AT scytek DOT de>
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To: cygwin AT cygwin DOT com
Subject: spawn doesn't return for non-cygwin programs (and also is unbreakable)
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Hi!

I recently tripped over the following problem: If a non-cygwin
program gets started by cygwin's spawnvp() the spawn doesn't return
until the started program returns.

To illustrate the problem just compile attached the attached
breaktestwin.c file as a cygwin executable

$ gcc breaktestwin.c -o breaktestwin.exe

and the attached wsleep.c as a native W32 executable

$ gcc -mno-cygwin wsleep.c -o wsleep.exe

and start breaktestwin.exe.

$ ./breaktestwin.exe

You will see that the "Started child  ..." message will not
appear until wsleep finishes.

This problem is actually known since 2001 but I thought it's
OK to mention it again. See:
<http://www.cygwin.com/ml/cygwin/2001-03/msg00068.html>

Another point that did not get mentioned AFAIK is that the
program is not interruptible by CTRL-c while spawnvp() is
waiting for it's "child". (Only true if CYGWIN=3Dtty or when
rxvt or something that handles tty's correctly is used.)

Try hitting CTRL-c while breaktestwin.exe is running from
a tty enable shell. The SIGINT will be handled after the
spawnvp() finishes.


Regards

   Volker


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 name="breaktestwin.c"
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 filename="breaktestwin.c"

#include <stdio.h>
#include <process.h>
#include <errno.h>
#include <signal.h>
#include <sys/wait.h>

void sigproc(int);
void quitproc(int);

int
main(void)
{
  pid_t pid1, wid;
  int status;

  char *cmnd[] =3D {"wsleep", "10", (char *)0 };

  signal(SIGINT, sigproc);
  signal(SIGQUIT, quitproc);=20

  pid1 =3D spawnvp(_P_NOWAIT, cmnd[0], (const char**) cmnd);
  fflush(stdout);
  if(pid1 =3D=3D -1) {
    fprintf(stderr,"%s : %s\n", cmnd[0], strerror(errno));
  }
  fprintf(stderr, "Started child pid: %d from parent %d\n", pid1, getpid());

  do {
     wid =3D wait(&status);
     fprintf(stderr, "wait returned: %d\n", wid);
  } while( wid !=3D pid1 );

  fprintf(stderr, "pid: %d wid: %d\nDone\n", pid1, wid);
}

void sigproc(int a) {
   fprintf(stderr, "you have pressed ctrl-c \n");
}
=20
void quitproc(int a) {
   fprintf(stderr, "ctrl-\\ pressed to quit\n");
//   exit(0); /* normal exit status */
}

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 name="wsleep.c"
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// Compile with MinGW
#include <stdio.h>
#include <windows.h>
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int main(int argc, char *argv[])
{  int wait;

   if( argc !=3D 2 ) {
      printf("wsleep takes exactly one argument!");
      return 1;
   }

   wait =3D abs(atoi(argv[1]));
   printf("Waiting %d sec ... ", wait);
   fflush (stdout);
   Sleep(1000*wait);
   printf("done\n");
   fflush (stdout);
=20=20=20
   return 0;
}


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