Lock-free GamepadSeqLock (try 2)

content/browser/gamepad/gamepad_provider_unittest.cc

Index: content/browser/gamepad/gamepad_provider_unittest.cc
===================================================================
--- content/browser/gamepad/gamepad_provider_unittest.cc	(revision 145136)
+++ content/browser/gamepad/gamepad_provider_unittest.cc	(working copy)
@@ -6,6 +6,7 @@
 #include "base/process_util.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/system_monitor/system_monitor.h"
+#include "base/threading/platform_thread.h"
 #include "content/browser/gamepad/data_fetcher.h"
 #include "content/browser/gamepad/gamepad_provider.h"
 #include "content/common/gamepad_hardware_buffer.h"
@@ -22,19 +23,14 @@
 class MockDataFetcher : public GamepadDataFetcher {
  public:
   explicit MockDataFetcher(const WebGamepads& test_data)
-      : test_data_(test_data),
-        read_data_(false, false) {
+      : test_data_(test_data) {
   }
   virtual void GetGamepadData(WebGamepads* pads,
                               bool devices_changed_hint) OVERRIDE {
     *pads = test_data_;
-    read_data_.Signal();
   }
 
-  void WaitForDataRead() { return read_data_.Wait(); }
-
   WebGamepads test_data_;
-  base::WaitableEvent read_data_;
 };
 
 // Main test fixture
@@ -77,8 +73,6 @@
 
   main_message_loop_.RunAllPending();
 
-  mock_data_fetcher_->WaitForDataRead();
-
   // Renderer-side, pull data out of poll buffer.
   base::SharedMemoryHandle handle =
       provider->GetRendererSharedMemoryHandle(base::GetCurrentProcessHandle());
@@ -88,15 +82,14 @@
   void* mem = shared_memory->memory();
 
   GamepadHardwareBuffer* hwbuf = static_cast<GamepadHardwareBuffer*>(mem);
-  // See gamepad_hardware_buffer.h for details on the read discipline.
   WebGamepads output;
-
-  base::subtle::Atomic32 version;
-  do {
-    version = hwbuf->sequence.ReadBegin();
-    memcpy(&output, &hwbuf->buffer, sizeof(output));
-  } while (hwbuf->sequence.ReadRetry(version));
-
+  output.length = 0;
+  for (;;) {
+    hwbuf->gamepads.ReadTo(&output);
+    if (output.length == 1)
+      break;
+    base::PlatformThread::YieldCurrentThread();
+  }
   EXPECT_EQ(1u, output.length);
   EXPECT_EQ(1u, output.items[0].buttonsLength);
   EXPECT_EQ(1.f, output.items[0].buttons[0]);