Tested x86_64-linux. Pushed to trunk.
I think we should backport this too, after some soak time on trunk.
-- >8 --
With -fno-elide-constructors the debug iterator post-increment and
post-decrement operators are susceptible to deadlock. They take a mutex
lock and then return a temporary, which also attempts to take a lock to
attach itself to the sequence. If the return value and *this happen to
collide and use the same mutex from the pool, then you get a deadlock
trying to lock a mutex that is already held by the current thread.
The solution is to construct the return value before taking the lock.
The copy constructor and pre-inc/pre-dec operators already manage locks
correctly, without deadlock, so just implement post-inc/post-dec in the
conventional way, taking a copy then modifying *this, then returning the
copy.
libstdc++-v3/ChangeLog:
PR libstdc++/108288
* include/debug/safe_iterator.h (_Safe_iterator::operator++(int))
(_Safe_iterator::operator--(int)): Do not hold lock around
construction of return value.
---
libstdc++-v3/include/debug/safe_iterator.h | 18 ++++++------------
1 file changed, 6 insertions(+), 12 deletions(-)
diff --git a/libstdc++-v3/include/debug/safe_iterator.h
b/libstdc++-v3/include/debug/safe_iterator.h
index 117dc93de60..f9068eaf8d6 100644
--- a/libstdc++-v3/include/debug/safe_iterator.h
+++ b/libstdc++-v3/include/debug/safe_iterator.h
@@ -761,12 +761,9 @@ namespace __gnu_debug
_Safe_iterator
operator++(int) _GLIBCXX_NOEXCEPT
{
- _GLIBCXX_DEBUG_VERIFY(this->_M_incrementable(),
- _M_message(__msg_bad_inc)
- ._M_iterator(*this, "this"));
- __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
- return _Safe_iterator(this->base()++, this->_M_sequence,
- _Attach_single());
+ _Safe_iterator __ret = *this;
+ ++*this;
+ return __ret;
}
// ------ Bidirectional iterator requirements ------
@@ -788,12 +785,9 @@ namespace __gnu_debug
_Safe_iterator
operator--(int) _GLIBCXX_NOEXCEPT
{
- _GLIBCXX_DEBUG_VERIFY(this->_M_decrementable(),
- _M_message(__msg_bad_dec)
- ._M_iterator(*this, "this"));
- __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
- return _Safe_iterator(this->base()--, this->_M_sequence,
- _Attach_single());
+ _Safe_iterator __ret = *this;
+ --*this;
+ return __ret;
}
// ------ Random access iterator requirements ------
--
2.39.0
