[libc++] Remove race condition in std::async
Summary:
The state associated to the future was set in one thread (with synchronization)
but read in another thread without synchronization, which led to a data race.
https://bugs.llvm.org/show_bug.cgi?id=38181
rdar://problem/42548261
Reviewers: mclow.lists, EricWF
Subscribers: christof, dexonsmith, cfe-commits
Differential Revision: https://reviews.llvm.org/D51170
llvm-svn: 340608
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 616ef1863faef8dedf2e6bfbaee7569d84f11e35
diff --git a/include/future b/include/future
index 0f6d426..b3ffc7e 100644
--- a/include/future
+++ b/include/future
@@ -556,13 +556,14 @@
{return (__state_ & __constructed) || (__exception_ != nullptr);}
_LIBCPP_INLINE_VISIBILITY
- void __set_future_attached()
- {
+ void __attach_future() {
lock_guard<mutex> __lk(__mut_);
+ bool __has_future_attached = (__state_ & __future_attached) != 0;
+ if (__has_future_attached)
+ __throw_future_error(future_errc::future_already_retrieved);
+ this->__add_shared();
__state_ |= __future_attached;
}
- _LIBCPP_INLINE_VISIBILITY
- bool __has_future_attached() const {return (__state_ & __future_attached) != 0;}
_LIBCPP_INLINE_VISIBILITY
void __set_deferred() {__state_ |= deferred;}
@@ -1154,10 +1155,7 @@
future<_Rp>::future(__assoc_state<_Rp>* __state)
: __state_(__state)
{
- if (__state_->__has_future_attached())
- __throw_future_error(future_errc::future_already_retrieved);
- __state_->__add_shared();
- __state_->__set_future_attached();
+ __state_->__attach_future();
}
struct __release_shared_count
@@ -1257,10 +1255,7 @@
future<_Rp&>::future(__assoc_state<_Rp&>* __state)
: __state_(__state)
{
- if (__state_->__has_future_attached())
- __throw_future_error(future_errc::future_already_retrieved);
- __state_->__add_shared();
- __state_->__set_future_attached();
+ __state_->__attach_future();
}
template <class _Rp>