[Runtime] Fix memory ordering on a store in ConcurrentReadableArray.

mikeash · mikeash · commit 58604ff1bae0 · 2020-08-26T13:24:44.000-04:00
diff --git a/include/swift/Runtime/Concurrent.h b/include/swift/Runtime/Concurrent.h
@@ -517,7 +517,7 @@ template <class ElemTy> struct ConcurrentReadableArray {
       auto *newStorage = Storage::allocate(newCapacity);
       if (storage) {
         std::copy(storage->data(), storage->data() + count, newStorage->data());
-        newStorage->Count.store(count, std::memory_order_relaxed);
+        newStorage->Count.store(count, std::memory_order_release);
         FreeList.push_back(storage);
       }
       

Original file line number	Diff line number	Diff line change
`@@ -517,7 +517,7 @@ template <class ElemTy> struct ConcurrentReadableArray {`
`517`	`517`	`auto *newStorage = Storage::allocate(newCapacity);`
`518`	`518`	`if (storage) {`
`519`	`519`	`std::copy(storage->data(), storage->data() + count, newStorage->data());`
`520`		`- newStorage->Count.store(count, std::memory_order_relaxed);`
	`520`	`+ newStorage->Count.store(count, std::memory_order_release);`
`521`	`521`	`FreeList.push_back(storage);`
`522`	`522`	`}`
`523`	`523`