New atomic operation foundation code and interfaces. Based on the atomic operations in google-perftools / tcmalloc.

- Makes atomic operations cross-platform (win/mac/linux).
- Supports 64 bit operations on 64 bit processors.
- Make atomic operations more correct on Windows (barriers).
- Introduces a better / safer interface, and abstracts away most common atomic operations, reference counting and sequence numbers.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@370 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 89 insertions, 0 deletions

diff --git a/base/atomic_ref_count.h b/base/atomic_ref_count.h
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+++ b/base/atomic_ref_count.h
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+// Copyright 2008, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// This is a low level implementation of atomic semantics for reference
+// counting.  Please use base/ref_counted.h directly instead.
+
+#ifndef BASE_ATOMIC_REF_COUNT_H_
+#define BASE_ATOMIC_REF_COUNT_H_
+
+#include "base/atomicops.h"
+#include "base/basictypes.h"
+
+namespace base {
+
+typedef base::subtle::Atomic32 AtomicRefCount;
+
+// Increment a reference count by "increment", which must exceed 0.
+inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr,
+                               AtomicRefCount increment) {
+  base::subtle::NoBarrier_AtomicIncrement(ptr, increment);
+}
+
+// Decrement a reference count by "decrement", which must exceed 0,
+// and return whether the result is non-zero.
+// Insert barriers to ensure that state written before the reference count
+// became zero will be visible to a thread that has just made the count zero.
+inline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr,
+                               AtomicRefCount decrement) {
+  return base::subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0;
+}
+
+// Increment a reference count by 1.
+inline void AtomicRefCountInc(volatile AtomicRefCount *ptr) {
+  base::AtomicRefCountIncN(ptr, 1);
+}
+
+// Decrement a reference count by 1 and return whether the result is non-zero.
+// Insert barriers to ensure that state written before the reference count
+// became zero will be visible to a thread that has just made the count zero.
+inline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) {
+  return base::AtomicRefCountDecN(ptr, 1);
+}
+
+// Return whether the reference count is one.  If the reference count is used
+// in the conventional way, a refrerence count of 1 implies that the current
+// thread owns the reference and no other thread shares it.  This call performs
+// the test for a reference count of one, and performs the memory barrier
+// needed for the owning thread to act on the object, knowing that it has
+// exclusive access to the object.
+inline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) {
+  return base::subtle::Acquire_Load(ptr) == 1;
+}
+
+// Return whether the reference count is zero.  With conventional object
+// referencing counting, the object will be destroyed, so the reference count
+// should never be zero.  Hence this is generally used for a debug check.
+inline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) {
+  return base::subtle::Acquire_Load(ptr) == 0;
+}
+
+}  // namespace base
+
+#endif  // BASE_ATOMIC_REF_COUNT_H_