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re PR libstdc++/54172 (__cxa_guard_acquire thread-safety issue) 

2012-09-09  Thiago Macieira  <thiago.macieira@intel.com>

	PR libstdc++/54172
        * libsupc++/guard.cc (__cxa_guard_acquire): Exit the loop earlier if
        we detect that another thread has had success. Don't compare_exchange
        from a finished state back to a waiting state. Comment.

From-SVN: r191125
This commit is contained in:
Thiago Macieira 2012-09-10 05:08:07 +00:00 committed by Benjamin Kosnik
parent 2e5edd2acc
commit 2fd7c76554
2 changed files with 23 additions and 3 deletions
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7
libstdc++-v3/ChangeLog
View File

@ -1,3 +1,10 @@
2012-09-09 Thiago Macieira <thiago.macieira@intel.com>
PR libstdc++/54172
* libsupc++/guard.cc (__cxa_guard_acquire): Exit the loop earlier if
we detect that another thread has had success. Don't compare_exchange
from a finished state back to a waiting state. Comment.
2012-09-09 Jonathan Wakely <jwakely.gcc@gmail.com>
PR libstdc++/54388

19
libstdc++-v3/libsupc++/guard.cc
View File

@ -244,13 +244,13 @@ namespace __cxxabiv1
if (__gthread_active_p ())
{
int *gi = (int *) (void *) g;
int expected(0);
const int guard_bit = _GLIBCXX_GUARD_BIT;
const int pending_bit = _GLIBCXX_GUARD_PENDING_BIT;
const int waiting_bit = _GLIBCXX_GUARD_WAITING_BIT;
while (1)
{
int expected(0);
if (__atomic_compare_exchange_n(gi, &expected, pending_bit, false,
__ATOMIC_ACQ_REL,
__ATOMIC_RELAXED))
@ -264,13 +264,26 @@ namespace __cxxabiv1
// Already initialized.
return 0;
}
if (expected == pending_bit)
{
// Use acquire here.
int newv = expected | waiting_bit;
if (!__atomic_compare_exchange_n(gi, &expected, newv, false,
__ATOMIC_ACQ_REL,
__ATOMIC_RELAXED))
continue;
__ATOMIC_ACQUIRE))
{
if (expected == guard_bit)
{
// Make a thread that failed to set the
// waiting bit exit the function earlier,
// if it detects that another thread has
// successfully finished initialising.
return 0;
}
if (expected == 0)
continue;
}
expected = newv;
}