This adds a check to weak_ptr::_M_assign() so that calling
__enable_shared_from_this_helper twice with the same pointer won't
change which shared_ptr object the weak_ptr shares ownership with.
On the lib reflector Peter Dimov convinced me that the
boost::enable_shared_from_this behaviour is preferable to what we do
now. I'm writing a proposal to specify this in the standard, but am
changing it now in our implementation.
Tested powerpc64le-linux, committing to trunk.
commit a1cd60820fb1af7f3396ff4b28e0e1d3449bfacb
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Tue Aug 25 17:10:36 2015 +0100
Only set std::enable_shared_from_this member once.
* include/bits/shared_ptr.h (__enable_shared_from_this_helper): Use
nullptr.
* include/bits/shared_ptr_base.h (weak_ptr::_M_assign): Don't assign
if ownership is already shared with a shared_ptr object.
(__enable_shared_from_this_helper): Use nullptr.
* testsuite/20_util/enable_shared_from_this/members/const.cc: New.
* testsuite/20_util/enable_shared_from_this/members/reinit.cc: New.
* testsuite/20_util/enable_shared_from_this/requirements/
explicit_instantiation.cc: Instantiate with const and incomplete types.
diff --git a/libstdc++-v3/include/bits/shared_ptr.h b/libstdc++-v3/include/bits/shared_ptr.h
index f96c078..2413b1b 100644
--- a/libstdc++-v3/include/bits/shared_ptr.h
+++ b/libstdc++-v3/include/bits/shared_ptr.h
@@ -588,7 +588,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
const enable_shared_from_this* __pe,
const _Tp1* __px) noexcept
{
- if (__pe != 0)
+ if (__pe != nullptr)
__pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
}
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h
index aec10fe..820edcb 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -1468,8 +1468,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
void
_M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
{
- _M_ptr = __ptr;
- _M_refcount = __refcount;
+ if (use_count() == 0)
+ {
+ _M_ptr = __ptr;
+ _M_refcount = __refcount;
+ }
}
template<typename _Tp1, _Lock_policy _Lp1> friend class __shared_ptr;
@@ -1549,7 +1552,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
const __enable_shared_from_this* __pe,
const _Tp1* __px) noexcept
{
- if (__pe != 0)
+ if (__pe != nullptr)
__pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
}
diff --git a/libstdc++-v3/testsuite/20_util/enable_shared_from_this/members/const.cc b/libstdc++-v3/testsuite/20_util/enable_shared_from_this/members/const.cc
new file mode 100644
index 0000000..fdf39c7
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/enable_shared_from_this/members/const.cc
@@ -0,0 +1,60 @@
+// Copyright (C) 2015 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/>.
+
+// { dg-options "-std=gnu++11" }
+
+#include <memory>
+#include <testsuite_hooks.h>
+
+template<typename T, typename U>
+ bool
+ share_ownership(const std::shared_ptr<T>& p1, const std::shared_ptr<U>& p2)
+ {
+ return !p1.owner_before(p2) && !p2.owner_before(p1);
+ }
+
+void
+test01()
+{
+ struct X : public std::enable_shared_from_this<X> { };
+ using CX = const X;
+ std::shared_ptr<CX> p(new X);
+ VERIFY( share_ownership(p->shared_from_this(), p) );
+ p.reset(new CX);
+ VERIFY( share_ownership(p->shared_from_this(), p) );
+ auto p2 = std::const_pointer_cast<X>(p)->shared_from_this();
+ VERIFY( share_ownership(p2, p) );
+}
+
+void
+test02()
+{
+ struct X;
+ using CX = const X;
+ struct X : public std::enable_shared_from_this<CX> { };
+ std::shared_ptr<CX> p(new X);
+ VERIFY( share_ownership(p->shared_from_this(), p) );
+ p.reset(new CX);
+ VERIFY( share_ownership(p->shared_from_this(), p) );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+}
diff --git a/libstdc++-v3/testsuite/20_util/enable_shared_from_this/members/reinit.cc b/libstdc++-v3/testsuite/20_util/enable_shared_from_this/members/reinit.cc
new file mode 100644
index 0000000..3740db8
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/enable_shared_from_this/members/reinit.cc
@@ -0,0 +1,49 @@
+// Copyright (C) 2015 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/>.
+
+// { dg-options "-std=gnu++11" }
+
+#include <memory>
+#include <testsuite_hooks.h>
+
+struct X : public std::enable_shared_from_this<X> { };
+
+bool
+share_ownership(const std::shared_ptr<X>& p1, const std::shared_ptr<X>& p2)
+{
+ return !p1.owner_before(p2) && !p2.owner_before(p1);
+}
+
+void
+test01()
+{
+ std::shared_ptr<X> p1(new X);
+ VERIFY( share_ownership( p1->shared_from_this(), p1 ) );
+ {
+ std::shared_ptr<X> p2(p1.get(), [](X*){});
+ // The weak_ptr member of the enable_shared_from_this base should not
+ // be reset by creating a second control block that owns the pointer.
+ VERIFY( share_ownership( p2->shared_from_this(), p1 ) );
+ }
+ VERIFY( share_ownership( p1->shared_from_this(), p1 ) );
+}
+
+int
+main()
+{
+ test01();
+}
diff --git a/libstdc++-v3/testsuite/20_util/enable_shared_from_this/requirements/explicit_instantiation.cc b/libstdc++-v3/testsuite/20_util/enable_shared_from_this/requirements/explicit_instantiation.cc
index 270ee84..94638e1 100644
--- a/libstdc++-v3/testsuite/20_util/enable_shared_from_this/requirements/explicit_instantiation.cc
+++ b/libstdc++-v3/testsuite/20_util/enable_shared_from_this/requirements/explicit_instantiation.cc
@@ -21,3 +21,8 @@
#include <memory>
template class std::enable_shared_from_this<int>;
+template class std::enable_shared_from_this<const int>;
+
+class Incomplete;
+template class std::enable_shared_from_this<Incomplete>;
+template class std::enable_shared_from_this<const Incomplete>;
