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Change the control flow in atomic_compare_exchange_strong to avoid a potential deadlock.

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When you assign a shared_ptr, the deleter gets called and assigned. In this routine, the assignment happens inside a critical section, which could (potentially) lead to a deadlock, if the deleter did something wonky. Now we swap the old value with an (empty) temporary shared_ptr, and then let the temporary delete the old value when it goes out of scope (after the lock has been released).  This should fix PR#27724. Thanks to Hans Boehm for the bug report and the suggested fix.



git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@269965 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Marshall Clow
2016-05-18 17:50:13 +00:00
parent a3388c6bb2
commit 2241cf0d5b
1 changed files with 3 additions and 0 deletions
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include/memory
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@@ -5541,14 +5541,17 @@ template <class _Tp>
bool bool
atomic_compare_exchange_strong(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) atomic_compare_exchange_strong(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w)
{ {
shared_ptr<_Tp> __temp;
__sp_mut& __m = __get_sp_mut(__p); __sp_mut& __m = __get_sp_mut(__p);
__m.lock(); __m.lock();
if (__p->__owner_equivalent(*__v)) if (__p->__owner_equivalent(*__v))
{ {
_VSTD::swap(__temp, *__p);
*__p = __w; *__p = __w;
__m.unlock(); __m.unlock();
return true; return true;
} }
_VSTD::swap(__temp, *__v);
*__v = *__p; *__v = *__p;
__m.unlock(); __m.unlock();
return false; return false;