Merge pull request #35383 from mikeash/fix-concurrentarray-memory-order3

mikeash · web-flow · commit 3d96554ad1fb · 2021-01-13T14:48:59.000-05:00
[Runtime] Make Concurrent.h ReaderCount loads seq_cst as well.
diff --git a/include/swift/Runtime/Concurrent.h b/include/swift/Runtime/Concurrent.h
@@ -538,7 +538,7 @@ template <class ElemTy> struct ConcurrentReadableArray {
     new(&storage->data()[count]) ElemTy(elem);
     storage->Count.store(count + 1, std::memory_order_release);
     
-    if (ReaderCount.load(std::memory_order_acquire) == 0)
+    if (ReaderCount.load(std::memory_order_seq_cst) == 0)
       deallocateFreeList();
   }
 
@@ -853,7 +853,7 @@ struct ConcurrentReadableHashMap {
   /// Free all the arrays in the free lists if there are no active readers. If
   /// there are active readers, do nothing.
   void deallocateFreeListIfSafe() {
-    if (ReaderCount.load(std::memory_order_acquire) == 0)
+    if (ReaderCount.load(std::memory_order_seq_cst) == 0)
       FreeListNode::freeAll(&FreeList);
   }
 

Original file line number	Diff line number	Diff line change
`@@ -538,7 +538,7 @@ template <class ElemTy> struct ConcurrentReadableArray {`
`538`	`538`	`new(&storage->data()[count]) ElemTy(elem);`
`539`	`539`	`storage->Count.store(count + 1, std::memory_order_release);`
`540`	`540`
`541`		`- if (ReaderCount.load(std::memory_order_acquire) == 0)`
	`541`	`+ if (ReaderCount.load(std::memory_order_seq_cst) == 0)`
`542`	`542`	`deallocateFreeList();`
`543`	`543`	`}`
`544`	`544`
`@@ -853,7 +853,7 @@ struct ConcurrentReadableHashMap {`
`853`	`853`	`/// Free all the arrays in the free lists if there are no active readers. If`
`854`	`854`	`/// there are active readers, do nothing.`
`855`	`855`	`void deallocateFreeListIfSafe() {`
`856`		`- if (ReaderCount.load(std::memory_order_acquire) == 0)`
	`856`	`+ if (ReaderCount.load(std::memory_order_seq_cst) == 0)`
`857`	`857`	`FreeListNode::freeAll(&FreeList);`
`858`	`858`	`}`
`859`	`859`