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Re: std::call_once without TLS
2009/4/26 Jonathan Wakely:
>
> Hmm, then a partial fix would be to retain the buggy
> __get_once_functor_lock() and the global lock object, for existing
> code which has inlined the current call_once(). ?That will work as
> long as it's not called concurrently.
Here's an ABI-compatible patch to fix libstdc++/39909, it would be
good if Chris or Benjamin could review it.
Code using the new ABI will use a lock object on the caller's stack
and provide a pointer to it, if the pointer is NULL then the caller is
using the old ABI the global lock object.
tested x86_64/linux with and without --disable-tls
Index: include/std/mutex
===================================================================
--- include/std/mutex (revision 146799)
+++ include/std/mutex (working copy)
@@ -729,8 +729,11 @@ namespace std
#else
extern function<void()> __once_functor;
- extern unique_lock<mutex>&
- __get_once_functor_lock();
+ extern void
+ __set_once_functor_lock_ptr(unique_lock<mutex>*);
+
+ extern mutex&
+ __get_once_mutex();
#endif
extern "C" void __once_proxy();
@@ -745,16 +748,16 @@ namespace std
__once_callable = &__bound_functor;
__once_call = &__once_call_impl<decltype(__bound_functor)>;
#else
- unique_lock<mutex>& __functor_lock = __get_once_functor_lock();
- __functor_lock.lock();
+ unique_lock<mutex> __functor_lock(__get_once_mutex());
__once_functor = bind(__f, __args...);
+ __set_once_functor_lock_ptr(&__functor_lock);
#endif
int __e = __gthread_once(&(__once._M_once), &__once_proxy);
#ifndef _GLIBCXX_HAVE_TLS
if (__functor_lock)
- __functor_lock.unlock();
+ __set_once_functor_lock_ptr(0);
#endif
if (__e)
Index: src/mutex.cc
===================================================================
--- src/mutex.cc (revision 146799)
+++ src/mutex.cc (working copy)
@@ -28,11 +28,11 @@
#ifndef _GLIBCXX_HAVE_TLS
namespace
{
- std::mutex&
- get_once_mutex()
+ inline std::unique_lock<std::mutex>*&
+ __get_once_functor_lock_ptr()
{
- static std::mutex once_mutex;
- return once_mutex;
+ static std::unique_lock<std::mutex>* __once_functor_lock_ptr = 0;
+ return __once_functor_lock_ptr;
}
}
#endif
@@ -55,10 +55,25 @@ namespace std
template class function<void()>;
function<void()> __once_functor;
+ mutex&
+ __get_once_mutex()
+ {
+ static mutex once_mutex;
+ return once_mutex;
+ }
+
+ // code linked against ABI 3.4.12 and later uses this
+ void
+ __set_once_functor_lock_ptr(unique_lock<mutex>* __ptr)
+ {
+ __get_once_functor_lock_ptr() = __ptr;
+ }
+
+ // unsafe - retained for compatibility with ABI 3.4.11
unique_lock<mutex>&
__get_once_functor_lock()
{
- static unique_lock<mutex> once_functor_lock(get_once_mutex(), defer_lock);
+ static unique_lock<mutex> once_functor_lock(__get_once_mutex(), defer_lock);
return once_functor_lock;
}
#endif
@@ -69,7 +84,14 @@ namespace std
{
#ifndef _GLIBCXX_HAVE_TLS
function<void()> __once_call = std::move(__once_functor);
- __get_once_functor_lock().unlock();
+ if (unique_lock<mutex>* __lock = __get_once_functor_lock_ptr())
+ {
+ // caller is using new ABI and provided lock ptr
+ __get_once_functor_lock_ptr() = 0;
+ __lock->unlock();
+ }
+ else
+ __get_once_functor_lock().unlock(); // global lock
#endif
__once_call();
}
Index: config/abi/pre/gnu.ver
===================================================================
--- config/abi/pre/gnu.ver (revision 146799)
+++ config/abi/pre/gnu.ver (working copy)
@@ -958,6 +958,14 @@ GLIBCXX_3.4.11 {
} GLIBCXX_3.4.10;
+GLIBCXX_3.4.12 {
+
+ # mutex
+ _ZSt27__set_once_functor_lock_ptrPSt11unique_lockISt5mutexE;
+ _ZSt16__get_once_mutexv;
+
+} GLIBCXX_3.4.11;
+
# Symbols in the support library (libsupc++) have their own tag.
CXXABI_1.3 {
Index: testsuite/util/testsuite_abi.cc
===================================================================
--- testsuite/util/testsuite_abi.cc (revision 146799)
+++ testsuite/util/testsuite_abi.cc (working copy)
@@ -183,6 +183,7 @@ check_version(symbol& test, bool added)
known_versions.push_back("GLIBCXX_3.4.9");
known_versions.push_back("GLIBCXX_3.4.10");
known_versions.push_back("GLIBCXX_3.4.11");
+ known_versions.push_back("GLIBCXX_3.4.12");
known_versions.push_back("GLIBCXX_LDBL_3.4");
known_versions.push_back("GLIBCXX_LDBL_3.4.7");
known_versions.push_back("GLIBCXX_LDBL_3.4.10");
Index: testsuite/30_threads/call_once/39909.cc
===================================================================
--- testsuite/30_threads/call_once/39909.cc (revision 0)
+++ testsuite/30_threads/call_once/39909.cc (revision 0)
@@ -0,0 +1,56 @@
+// { dg-do run { target *-*-freebsd* *-*-netbsd* *-*-linux* *-*-solaris* *-*-cygwin *-*-darwin* alpha*-*-osf* mips-sgi-irix6* } }
+// { dg-options " -std=gnu++0x -pthread" { target *-*-freebsd* *-*-netbsd* *-*-linux* alpha*-*-osf* mips-sgi-irix6* } }
+// { dg-options " -std=gnu++0x -pthreads" { target *-*-solaris* } }
+// { dg-options " -std=gnu++0x " { target *-*-cygwin *-*-darwin* } }
+// { dg-require-cstdint "" }
+// { dg-require-gthreads "" }
+
+// Copyright (C) 2009 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+
+#include <mutex>
+#include <thread>
+#include <testsuite_hooks.h>
+
+std::once_flag flag;
+int value = 0;
+
+struct Inc { void operator()() const { ++value; } };
+
+struct Func
+{
+ void operator()() const
+ {
+ Inc inc;
+ for (int i = 0; i < 10000; ++i)
+ std::call_once(flag, inc);
+ }
+};
+
+int main()
+{
+ Func f;
+ std::thread t1(f);
+ std::thread t2(f);
+ std::thread t3(f);
+ t1.join();
+ t2.join();
+ t3.join();
+ VERIFY( value == 1 );
+ return 0;
+}