libstdc++: Fix deadlock in debug iterator increment [PR108288]

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.

0 files changed, 0 insertions, 0 deletions