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Date:	Wed, 19 Feb 2014 19:46:48 +0100
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: Bug with dlopen() and fork()
Message-ID:	<20140219184648.GW2246@calimero.vinschen.de>
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On Feb 19 14:38, Jaime Fabregas Fernandez wrote:
> Library references loaded by a process using dlopen() and dlsym() are
> no more valid in child processes after running a fork(). Calls from
> child process will never return.
>=20
> I've searched for a similar problem in the mailing lists and found
> this unanswered thread from 2001:
>=20
> http://cygwin.com/ml/cygwin/2001-02/msg01225.html
>=20
>=20
> I'm running cygwin64. This behaviour can be checked with the following
> test program:
>=20
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D
> #include <stdio.h>
> #include <dlfcn.h>
>=20
> int (*myopen)(const char *);
>=20
> main(){
>         void *handle;
>         int ret;
>         handle =3D dlopen("my_lib.dll", RTLD_LAZY);
>         myopen =3D dlsym(handle, "mylib_open");
>=20
>         if( ! fork() ){
>                 ret =3D myopen("");
>                 printf("This printf never shows, call to myopen will
> block for ever\n");
>         }
>         else{
>                 ret =3D myopen("");
>                 printf("%i\n", ret);
>                 sleep(1);
>         }
> }
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D
>=20
> Same program runs correctly (showing the two printf's) in a Linux environ=
ment.

Works for me with 64 bit Cygwin.  I used this as DLL:

  $ cat > my_lib.c <<EOF
  int
  mylib_open (const char *foo)
  {
    return 1;
  }
  $ gcc -shared -o my_lib.dll my_lib.c
  $ gcc -g -o my_tst my_tst.c		<- That's your above testcase
  $ uname -a
  CYGWIN_NT-6.3 vmbert8164 1.7.28(0.271/5/3) 2014-02-04 16:01 x86_64 Cygwin
  $ ./my_tst
  1
  This printf never shows, call to myopen will block for ever
  $


Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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