Allow linker initialization of lazy instance

base/lazy_instance.cc

 // Copyright (c) 2011 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/threading/platform_thread.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 
 namespace base {
+namespace internal {
 
-bool LazyInstanceHelper::NeedsInstance() {
+// TODO(joth): This function could be shared with Singlton, in place of its
+// WaitForInstance() call.
+bool NeedsLazyInstance(base::subtle::AtomicWord* state) {
   // Try to create the instance, if we're the first, will go from EMPTY
   // to CREATING, otherwise we've already been beaten here.
   // The memory access has no memory ordering as STATE_EMPTY and STATE_CREATING
   // has no associated data (memory barriers are all about ordering
   // of memory accesses to *associated* data).
   if (base::subtle::NoBarrier_CompareAndSwap(
-          &state_, STATE_EMPTY, STATE_CREATING) == STATE_EMPTY)
+          state, 0, internal::kLazyInstanceStateCreating) == 0)

[willchan no longer on Chromium, 2011/11/11 22:18:21]

Already within internal namespace, no need for internal::.

[joth, 2011/11/14 16:58:23]

Done.

     // Caller must create instance
     return true;
 
   // It's either in the process of being created, or already created. Spin.
   // The load has acquire memory ordering as a thread which sees
   // state_ == STATE_CREATED needs to acquire visibility over
   // the associated data (buf_). Pairing Release_Store is in
   // CompleteInstance().
-  while (base::subtle::Acquire_Load(&state_) != STATE_CREATED)
+  while (base::subtle::Acquire_Load(state) ==
+      internal::kLazyInstanceStateCreating) {
     PlatformThread::YieldCurrentThread();
-
+  }
   // Someone else created the instance.
   return false;
 }
 
-void LazyInstanceHelper::CompleteInstance(void* instance, void (*dtor)(void*)) {
+void CompleteLazyInstance(base::subtle::AtomicWord* state,
+                          base::subtle::AtomicWord new_instance,
+                          void* lazy_instance,
+                          void (*dtor)(void*)) {
   // See the comment to the corresponding HAPPENS_AFTER in Pointer().
-  ANNOTATE_HAPPENS_BEFORE(&state_);
+  ANNOTATE_HAPPENS_BEFORE(state);
 
   // Instance is created, go from CREATING to CREATED.
-  // Releases visibility over buf_ to readers. Pairing Acquire_Load's are in
-  // NeedsInstance() and Pointer().
-  base::subtle::Release_Store(&state_, STATE_CREATED);
+  // Releases visibility over private_buf_ to readers. Pairing Acquire_Load's
+  // are in NeedsInstance() and Pointer().
+  base::subtle::Release_Store(state, new_instance);
 
   // Make sure that the lazily instantiated object will get destroyed at exit.
   if (dtor)
-    base::AtExitManager::RegisterCallback(dtor, instance);
+    base::AtExitManager::RegisterCallback(dtor, lazy_instance);
 }
 
+}  // namespace internal
 }  // namespace base
 
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