Re: [PATCH v3] Destructor support for C++11 thread_local variables- abilist entries

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

Ping, any feedback on this?  I'm also waiting for Jakub or Jason to
confirm if thread_local is definitely going to make it into gcc-4.8.
If it is then I could write the test case into glibc.

http://sourceware.org/ml/libc-alpha/2012-10/msg00444.html

Thanks,
Siddhesh

On Wed, 17 Oct 2012 18:40:33 +0530, Siddhesh wrote:

> Hi,
> 
> Here is an updated patch based on feedback so far.  For context of
> this change, please see the following thread:
> 
> http://sourceware.org/ml/libc-alpha/2012-10/msg00289.html
> 
> To summarize, this patch adds destructor support for the C++11
> variables of the thread_local scope.  it adds a new function
> __cxa_thread_atexit_impl, that libstdc++ calls to register destructors
> for the thread_local objects it constructs.  The destructors will then
> be called at either thread exit or program exit.  The current
> iteration of the patch adds support to allow unloading a DSO that has
> thread_local variables provided that all threads that constructed the
> variables have exited and their destructors called.  This is
> implemented by adding an extra field in struct link_map to count the
> destructors that were registered, decrementing when a destructor is
> called.
> 
> I have verified that the latter functionality works with the help of
> the following program:
> 
> $ cat foo.cc:
> 
> #include "thread_local.h"
> extern "C" void do_foo (void)
> {
>   thread_local A b;
> }
> 
> $ cat thread_local.cc:
> 
> #include <dlfcn.h>
> #include <pthread.h>
> #include <stdio.h>
> #include <unistd.h>
> #include "thread_local.h"
> 
> int c;
> int d;
> 
> void (*foo) (void);
> pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
> 
> void f()
> {
>   thread_local A a;
> }
> 
> void *
> load (void *u)
> {
>   pthread_mutex_lock (&m);
>   void *h = dlopen ("./libfoo.so", RTLD_LAZY);
>   foo = (void (*) (void)) dlsym(h, "do_foo");
> 
>   foo ();
>   dlclose (h);
>   pthread_mutex_unlock (&m);
> }
> 
> void *
> thr (void *u)
> {
>   /* wait till foo is initialized.  */
>   while (!foo);   
> 
>   pthread_mutex_lock (&m);
>   foo ();
>   pthread_mutex_unlock (&m);
> }
> 
> int main()
> {
> 
>   pthread_t t, dsot;
> 
>   pthread_create (&t, NULL, thr, NULL);
>   sleep (1);
>   pthread_create (&dsot, NULL, load, NULL);
> 
>   pthread_join (t, NULL);
>   pthread_join (dsot, NULL);
>   printf ("%d, %d\n", c, d);
> }
> 
> $ tls-g++ -g -fPIC -std=c++11 thread_local.cc -ldl -pthread
> $ tls-g++ -fPIC -std=c++11 -shared -o libfoo.so foo.cc
> 
> 
> Regards,
> Siddhesh
> 
> ChangeLog:
> 
> 	* include/link.h (struct link_map): New member
> l_tls_dtor_count.
> 	* include/stdlib.h (__cxa_thread_atexit_impl): Declare.
> 	(__call_tls_dtors): Likewise.
> 	* sysdeps/unix/sysv/linux/i386/nptl/libc.abilist: Add
> 	__cxa_thread_atexit_impl.
> 	*
> sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/nptl/libc.abilist:
> Likewise.
> 	* sysdeps/unix/sysv/linux/powerpc/powerpc64/nptl/libc.abilist:
> 	Likewise.
> 	* sysdeps/unix/sysv/linux/s390/s390-32/nptl/libc.abilist:
> 	Likewise.
> 	* sysdeps/unix/sysv/linux/s390/s390-64/nptl/libc.abilist:
> 	Likewise.
> 	* sysdeps/unix/sysv/linux/sh/nptl/libc.abilist: Likewise.
> 	* sysdeps/unix/sysv/linux/sparc/sparc32/nptl/libc.abilist:
> 	Likewise.
> 	* sysdeps/unix/sysv/linux/sparc/sparc64/nptl/libc.abilist:
> 	Likewise.
> 	* sysdeps/unix/sysv/linux/x86_64/64/nptl/libc.abilist:
> Likewise.
> 	* sysdeps/unix/sysv/linux/x86_64/x32/nptl/libc.abilist:
> 	Likewise.
> 	* stdlib/Makefile (routines): Add __cxa_thread_atexit_impl.
> 	* stdlib/Versions (GLIBC_2.17): Likewise.
> 	(GLIBC_PRIVATE): Add __call_tls_dtors.
> 	* stdlib/cxa_thread_atexit_impl.c: New file with helper
> function for libstdc++.
> 	* stdlib/exit.c (__run_exit_handlers): Call __call_tls_dtors.
> 
> nptl/ChangeLog:
> 
> 	* pthread_create.c (start_thread): Call __call_tls_dtors.
> 
> ChangeLog.alpha:
> 2012-10-11  Siddhesh Poyarekar  <siddhesh@redhat.com>
> 
> 	* sysdeps/unix/sysv/linux/alpha/nptl/libc.abilist: Add
> 	__cxa_thread_atexit_impl.
> 
> 
> ChangeLog.arm:
> 2012-10-11  Siddhesh Poyarekar  <siddhesh@redhat.com>
> 
> 	* sysdeps/unix/sysv/linux/arm/nptl/libc.abilist: Add
> 	__cxa_thread_atexit_impl.
> 
> 
> ChangeLog.ia64:
> 2012-10-11  Siddhesh Poyarekar  <siddhesh@redhat.com>
> 
> 	* sysdeps/unix/sysv/linux/ia64/nptl/libc.abilist: Add
> 	__cxa_thread_atexit_impl.
> 
> 
> ChangeLog.m68k:
> 2012-10-11  Siddhesh Poyarekar  <siddhesh@redhat.com>
> 
> 	* sysdeps/unix/sysv/linux/m68k/coldfire/nptl/libc.abilist: Add
> 	__cxa_thread_atexit_impl.
> 	* sysdeps/unix/sysv/linux/m68k/m680x0/nptl/libc.abilist:
> 	Likewise.
> 
> 
> ChangeLog.mips:
> 2012-10-11  Siddhesh Poyarekar  <siddhesh@redhat.com>
> 
> 	* sysdeps/unix/sysv/linux/mips/mips32/nptl/libc.abilist: Add
> 	__cxa_thread_atexit_impl.
> 	* sysdeps/unix/sysv/linux/mips/mips64/n32/nptl/libc.abilist:
> 	Likewise.