Allow linker initialization of lazy instance

Using the initializer list construct = {0} allows the object to be linker initialized.
Modify the LazyInstance class design to make it a pod aggregate type that can be linker initialized this way. Also combines the instance and state members, in line with the Singleton<> class design.
Introduces a new LAZY_INSTANCE_INITIALIZER macro specifically for using to init all lazy instances + modify all existing callsites to use it. (Old code would no longer compile)

BUG=94925
TEST=existing tests pass. http://build.chromium.org/f/chromium/perf/linux-release/sizes/report.html?history=150&header=chrome-si&graph=chrome-si&rev=-1 should step downward.
TBR=jam@chromium.org,rvargas@chromium.org,darin@chromium.org,ben@chromium.org,apatrick@chromium.org,akalin@chromium.org

Review URL: http://codereview.chromium.org/8491043

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@110076 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 25 insertions, 21 deletions

diff --git a/base/lazy_instance.cc b/base/lazy_instance.cc
index 1be3488..a81cb8c 100644
--- a/base/lazy_instance.cc
+++ b/base/lazy_instance.cc
@@ -11,15 +11,18 @@
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 
 namespace base {
-
-bool LazyInstanceHelper::NeedsInstance() {
-  // 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)
+namespace internal {
+
+// TODO(joth): This function could be shared with Singleton, in place of its
+// WaitForInstance() call.
+bool NeedsLazyInstance(subtle::AtomicWord* state) {
+  // Try to create the instance, if we're the first, will go from 0 to
+  // kLazyInstanceStateCreating, otherwise we've already been beaten here.
+  // The memory access has no memory ordering as state 0 and
+  // kLazyInstanceStateCreating have no associated data (memory barriers are
+  // all about ordering of memory accesses to *associated* data).
+  if (subtle::NoBarrier_CompareAndSwap(state, 0,
+                                       kLazyInstanceStateCreating) == 0)
     // Caller must create instance
     return true;
 
@@ -27,29 +30,30 @@ bool LazyInstanceHelper::NeedsInstance() {
   // 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)
+  // CompleteLazyInstance().
+  while (subtle::Acquire_Load(state) == kLazyInstanceStateCreating) {
     PlatformThread::YieldCurrentThread();
-
+  }
   // Someone else created the instance.
   return false;
 }
 
-void LazyInstanceHelper::CompleteInstance(void* instance, void (*dtor)(void*)) {
+void CompleteLazyInstance(subtle::AtomicWord* state,
+                          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().
+  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);
+    AtExitManager::RegisterCallback(dtor, lazy_instance);
 }
 
+}  // namespace internal
 }  // namespace base
-
-
-