Re: pthread_atfork() problem on Linux9

[John <red@xxxxxxxxxxxxxxxxxxxxxxx>]

On Thu, 3 Apr 2003 Tushar_Oza@xxxxxxxx wrote:

> Hello,
> 
> A brief description of the problem we see on Linux 9 follows:
> 
> Please let me know if any of you have seen this problem or know how to
> tackle it!
> 
> 
> I have a "mylib.so" that calls:
> 
> _init()
> {
>    pthread_atfork(NULL, ParentHdlr, ChildHdlr);
> }
> 
> _fini()
> {
>    // do nothing
+    printf(unloading\n");
> }
> 
> 
> Another executable mytest.c does the following:
> 
> main()
> {
>   void *libHandle = NULL;
> 
>   libHandle = dlopen("mylib.so", RTLD_NOW);
>   // dlopen() call succeeds so I have not included my error checking code
> here
>   dlclose(libHandle);
>   libHandle = NULL;
>   ...
>   printf("\n In mytest.c: Before fork \n");
> 
>   if ((pid = fork()) < 0)
>   {
>      printf("Fork failed\n");
>   }
> 
>   printf("Something after fork\n");
> }
> 
> 
> Note that the fork() is called after the dlclose()
> And mytest.c is NOT linked with mylib.so
> 
> The problem is mytest.c causes a SEGMENTATION FAULT on Linux9. Seems to work
> fine on Linux 8 and below.
> 
> We suspect that the atfork() handler functions registered at _init are lost
> And that causes the seg fault before the fork() since it cant find the
> handlers anymore as the library has been closed.
> 
> Any help is appreciated. Thanks!
>From the man page on my system:

      dlclose decrements the reference count on the dynamic library
handle handle.  If the reference count drops to zero and no other loaded
libraries use symbols in it, then the dynamic library is unloaded.  If
the  dynamic  library exports a routine named _fini, then that routine
is called just before the library is unloaded.


I think unloading is legitimate. Try my patch to see whether it happens.

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