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8280832: Update usage docs for NonblockingQueue

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Reviewed-by: iwalulya, dholmes
This commit is contained in:
Kim Barrett 2022-02-10 11:28:04 +00:00
parent d442328bc2
commit 3ce1c5b6ce
2 changed files with 9 additions and 1 deletions
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4
src/hotspot/share/utilities/nonblockingQueue.hpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2021, 2022, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -96,9 +96,11 @@ public:
inline size_t length() const;
// Thread-safe add the object to the end of the queue.
// Subject to ABA behavior; callers must ensure usage is safe.
inline void push(T& node) { append(node, node); }
// Thread-safe add the objects from first to last to the end of the queue.
// Subject to ABA behavior; callers must ensure usage is safe.
inline void append(T& first, T& last);
// Thread-safe attempt to remove and return the first object in the queue.

6
src/hotspot/share/utilities/nonblockingQueue.inline.hpp
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@ -117,6 +117,12 @@ void NonblockingQueue<T, next_ptr>::append(T& first, T& last) {
// other push/append could have competed with us, because we claimed
// old_tail for extension. We won any races with try_pop by changing
// away from end-marker. So we're done.
//
// Note that ABA is possible here. A concurrent try_pop could take
// old_tail before our update of old_tail's next_ptr, old_tail gets
// recycled and re-added to the end of this queue, and then we
// successfully cmpxchg, making the list in _tail circular. Callers
// must ensure this can't happen.
return;
} else {
// A concurrent try_pop has claimed old_tail, so it is no longer in the