diff options
| author | bkoz <bkoz@138bc75d-0d04-0410-961f-82ee72b054a4> | 2012-09-06 20:31:08 +0000 |
|---|---|---|
| committer | bkoz <bkoz@138bc75d-0d04-0410-961f-82ee72b054a4> | 2012-09-06 20:31:08 +0000 |
| commit | 67518851535a5303a126201b2c68508c369f96ef (patch) | |
| tree | fc46d4517215160085224e179732892943443922 /libstdc++-v3 | |
| parent | f819bb7398c28c88bd12f95589ebae74d837cad4 (diff) | |
| download | gcc-67518851535a5303a126201b2c68508c369f96ef.tar.gz | |
2012-09-06 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.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@191042 138bc75d-0d04-0410-961f-82ee72b054a4
Diffstat (limited to 'libstdc++-v3')
| -rw-r--r-- | libstdc++-v3/ChangeLog | 7 | ||||
| -rw-r--r-- | libstdc++-v3/libsupc++/guard.cc | 19 |
2 files changed, 23 insertions, 3 deletions
diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index 707e474b899..f3a5852dd21 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,10 @@ +2012-09-06 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. + 2012-09-05 François Dumont <fdumont@gcc.gnu.org> PR libstdc++/54296 diff --git a/libstdc++-v3/libsupc++/guard.cc b/libstdc++-v3/libsupc++/guard.cc index adc96086108..60165cdecb4 100644 --- a/libstdc++-v3/libsupc++/guard.cc +++ b/libstdc++-v3/libsupc++/guard.cc @@ -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; } |