Create a LazyInstance abstraction for avoiding static constructors by lazily creating an instance of an object on first access. This is like Singleton, but without the Singleton property of sharing instances. This also preallocates space for the object to avoid the heap to try to help fragmentation and creation performance.

Review URL: http://codereview.chromium.org/1608

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@1837 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 34 insertions, 0 deletions

diff --git a/base/lazy_instance.cc b/base/lazy_instance.cc
new file mode 100644
index 0000000..3f089e0
--- /dev/null
+++ b/base/lazy_instance.cc
@@ -0,0 +1,34 @@
+// Copyright (c) 2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/lazy_instance.h"
+
+#include "base/at_exit.h"
+#include "base/atomicops.h"
+#include "base/basictypes.h"
+#include "base/platform_thread.h"
+
+namespace base {
+
+void LazyInstanceHelper::EnsureInstance(void* instance,
+                                        void (*ctor)(void*),
+                                        void (*dtor)(void*)) {
+  // Try to create the instance, if we're the first, will go from EMPTY
+  // to CREATING, otherwise we've already been beaten here.
+  if (base::subtle::Acquire_CompareAndSwap(
+          &state_, STATE_EMPTY, STATE_CREATING) == STATE_EMPTY) {
+    // Created the instance in the space provided by |instance|.
+    ctor(instance);
+    // Instance is created, go from CREATING to CREATED.
+    base::subtle::Release_Store(&state_, STATE_CREATED);
+    // Register the destructor callback with AtExitManager.
+    base::AtExitManager::RegisterCallback(dtor, instance);
+  } else {
+    // It's either in the process of being created, or already created.  Spin.
+    while (base::subtle::NoBarrier_Load(&state_) != STATE_CREATED)
+      PlatformThread::YieldCurrentThread();
+  }
+}
+
+}  // namespace base