[gcc(refs/users/guojiufu/heads/guojiufu-branch)] libstdc++ Enhance thread safety of debug mode iterators
Jiu Fu Guo
guojiufu@gcc.gnu.org
Tue May 12 07:06:01 GMT 2020
https://gcc.gnu.org/g:0b83c4fabb899fdbb3ae60ed75b7004b7859fae9
commit 0b83c4fabb899fdbb3ae60ed75b7004b7859fae9
Author: François Dumont <fdumont@gcc.gnu.org>
Date: Sat Feb 29 18:22:55 2020 +0100
libstdc++ Enhance thread safety of debug mode iterators
Avoids race condition when checking for an iterator to be singular or
to be comparable to another iterator.
* src/c++/debug.cc
(_Safe_sequence_base::_M_attach_single): Set attached iterator
sequence pointer and version.
(_Safe_sequence_base::_M_detach_single): Reset detached iterator.
(_Safe_iterator_base::_M_attach): Remove attached iterator sequence
pointer and version asignments.
(_Safe_iterator_base::_M_attach_single): Likewise.
(_Safe_iterator_base::_M_detach_single): Remove detached iterator
reset.
(_Safe_iterator_base::_M_singular): Use atomic load to access parent
sequence.
(_Safe_iterator_base::_M_can_compare): Likewise.
(_Safe_iterator_base::_M_get_mutex): Likewise.
(_Safe_local_iterator_base::_M_attach): Remove attached iterator container
pointer and version assignments.
(_Safe_local_iterator_base::_M_attach_single): Likewise.
(_Safe_unordered_container_base::_M_attach_local_single):
Set attached iterator container pointer and version.
(_Safe_unordered_container_base::_M_detach_local_single): Reset detached
iterator.
Diff:
---
libstdc++-v3/ChangeLog | 23 +++++++++++++++++
libstdc++-v3/src/c++11/debug.cc | 57 +++++++++++++++++++++--------------------
2 files changed, 52 insertions(+), 28 deletions(-)
diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index a2ff49d9e51..8fb6b86474b 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,26 @@
+2020-05-10 François Dumont <fdumont@gcc.gnu.org>
+
+ * src/c++/debug.cc
+ (_Safe_sequence_base::_M_attach_single): Set attached iterator
+ sequence pointer and version.
+ (_Safe_sequence_base::_M_detach_single): Reset detached iterator.
+ (_Safe_iterator_base::_M_attach): Remove attached iterator sequence
+ pointer and version asignments.
+ (_Safe_iterator_base::_M_attach_single): Likewise.
+ (_Safe_iterator_base::_M_detach_single): Remove detached iterator
+ reset.
+ (_Safe_iterator_base::_M_singular): Use atomic load to access parent
+ sequence.
+ (_Safe_iterator_base::_M_can_compare): Likewise.
+ (_Safe_iterator_base::_M_get_mutex): Likewise.
+ (_Safe_local_iterator_base::_M_attach): Remove attached iterator container
+ pointer and version assignments.
+ (_Safe_local_iterator_base::_M_attach_single): Likewise.
+ (_Safe_unordered_container_base::_M_attach_local_single):Set attached
+ iterator container pointer and version.
+ (_Safe_unordered_container_base::_M_detach_local_single): Reset detached
+ iterator.
+
2020-05-07 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/94971 (partial)
diff --git a/libstdc++-v3/src/c++11/debug.cc b/libstdc++-v3/src/c++11/debug.cc
index 18da9da9c52..032e0b50b91 100644
--- a/libstdc++-v3/src/c++11/debug.cc
+++ b/libstdc++-v3/src/c++11/debug.cc
@@ -318,6 +318,8 @@ namespace __gnu_debug
_Safe_sequence_base::
_M_attach_single(_Safe_iterator_base* __it, bool __constant) throw ()
{
+ __it->_M_sequence = this;
+ __it->_M_version = _M_version;
_Safe_iterator_base*& __its =
__constant ? _M_const_iterators : _M_iterators;
__it->_M_next = __its;
@@ -345,6 +347,7 @@ namespace __gnu_debug
_M_const_iterators = __it->_M_next;
if (_M_iterators == __it)
_M_iterators = __it->_M_next;
+ __it->_M_reset();
}
void
@@ -355,11 +358,7 @@ namespace __gnu_debug
// Attach to the new sequence (if there is one)
if (__seq)
- {
- _M_sequence = __seq;
- _M_version = _M_sequence->_M_version;
- _M_sequence->_M_attach(this, __constant);
- }
+ __seq->_M_attach(this, __constant);
}
void
@@ -370,11 +369,7 @@ namespace __gnu_debug
// Attach to the new sequence (if there is one)
if (__seq)
- {
- _M_sequence = __seq;
- _M_version = _M_sequence->_M_version;
- _M_sequence->_M_attach_single(this, __constant);
- }
+ __seq->_M_attach_single(this, __constant);
}
void
@@ -400,10 +395,7 @@ namespace __gnu_debug
_M_detach_single() throw ()
{
if (_M_sequence)
- {
- _M_sequence->_M_detach_single(this);
- _M_reset();
- }
+ _M_sequence->_M_detach_single(this);
}
void
@@ -419,20 +411,32 @@ namespace __gnu_debug
bool
_Safe_iterator_base::
_M_singular() const throw ()
- { return !_M_sequence || _M_version != _M_sequence->_M_version; }
+ {
+ auto seq = __atomic_load_n(&_M_sequence, __ATOMIC_ACQUIRE);
+ return !seq || _M_version != seq->_M_version;
+ }
bool
_Safe_iterator_base::
_M_can_compare(const _Safe_iterator_base& __x) const throw ()
{
- return (!_M_singular()
- && !__x._M_singular() && _M_sequence == __x._M_sequence);
+ auto seq = __atomic_load_n(&_M_sequence, __ATOMIC_ACQUIRE);
+ if (seq && _M_version == seq->_M_version)
+ {
+ auto xseq = __atomic_load_n(&__x._M_sequence, __ATOMIC_ACQUIRE);
+ return xseq && __x._M_version == xseq->_M_version && seq == xseq;
+ }
+
+ return false;
}
__gnu_cxx::__mutex&
_Safe_iterator_base::
_M_get_mutex() throw ()
- { return _M_sequence->_M_get_mutex(); }
+ {
+ auto seq = __atomic_load_n(&_M_sequence, __ATOMIC_ACQUIRE);
+ return get_safe_base_mutex(seq);
+ }
_Safe_unordered_container_base*
_Safe_local_iterator_base::
@@ -447,11 +451,8 @@ namespace __gnu_debug
// Attach to the new container (if there is one)
if (__cont)
- {
- _M_sequence = __cont;
- _M_version = _M_sequence->_M_version;
- _M_get_container()->_M_attach_local(this, __constant);
- }
+ static_cast<_Safe_unordered_container_base*>(__cont)
+ ->_M_attach_local(this, __constant);
}
void
@@ -462,11 +463,8 @@ namespace __gnu_debug
// Attach to the new container (if there is one)
if (__cont)
- {
- _M_sequence = __cont;
- _M_version = _M_sequence->_M_version;
- _M_get_container()->_M_attach_local_single(this, __constant);
- }
+ static_cast<_Safe_unordered_container_base*>(__cont)
+ ->_M_attach_local_single(this, __constant);
}
void
@@ -526,6 +524,8 @@ namespace __gnu_debug
_Safe_unordered_container_base::
_M_attach_local_single(_Safe_iterator_base* __it, bool __constant) throw ()
{
+ __it->_M_sequence = this;
+ __it->_M_version = _M_version;
_Safe_iterator_base*& __its =
__constant ? _M_const_local_iterators : _M_local_iterators;
__it->_M_next = __its;
@@ -553,6 +553,7 @@ namespace __gnu_debug
_M_const_local_iterators = __it->_M_next;
if (_M_local_iterators == __it)
_M_local_iterators = __it->_M_next;
+ __it->_M_reset();
}
}
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