Generic version of caching cc switches to avoid searching of switches on each function call

cc/base/switches.cc

 // Copyright (c) 2012 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 "cc/base/switches.h"
 
 #include "base/command_line.h"
 
 namespace cc {
 namespace switches {
@@ skipping 133 matching lines @@
 // Makes pixel tests write their output instead of read it.
 const char kCCRebaselinePixeltests[] = "cc-rebaseline-pixeltests";
 
 // Disable textures using RGBA_4444 layout.
 const char kDisable4444Textures[] = "disable-4444-textures";
 
 // Disable touch hit testing in the compositor.
 const char kDisableCompositorTouchHitTesting[] =
     "disable-compositor-touch-hit-testing";
 
-bool IsLCDTextEnabled() {
-  const CommandLine* command_line = CommandLine::ForCurrentProcess();
-  if (command_line->HasSwitch(cc::switches::kDisableLCDText))
-    return false;
-  else if (command_line->HasSwitch(cc::switches::kEnableLCDText))
-    return true;
+struct Switches {
+  Switches()
+    : has_initialized_switches_(false)
+    , impl_side_painting_enabled_(false)
+    , map_image_enabled_(false)
+    , lcd_text_enabled_(false) {
+  }
 
+  bool has_initialized_switches_ : 1;
+  bool impl_side_painting_enabled_ : 1;
+  bool map_image_enabled_ : 1;
+  bool lcd_text_enabled_ : 1;
+};
+static Switches g_switches;

[vivekg, 2013/11/20 01:50:15]

How about moving this global variable as local static inside the
InitializeSwitchesIfRequired() as-

void InitializeSwitchesIfRequired() {
  static Switches switches;

  if (switches.has_initialized_switches_)
    return;
  ...
}

[danakj, 2013/11/20 01:55:21]

Then it would also have to return a const Switches&. I'm not sure what this buys
though?

+
+void InitializeSwitchesIfRequired() {
+  if (g_switches.has_initialized_switches_)
+    return;
+
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+  // Impl-side painting.
+  if (command_line.HasSwitch(cc::switches::kDisableImplSidePainting)) {
+    g_switches.impl_side_painting_enabled_ = false;
+  } else if (command_line.HasSwitch(cc::switches::kEnableImplSidePainting)) {
+    g_switches.impl_side_painting_enabled_ = true;
+  } else {
 #if defined(OS_ANDROID)
-  return false;
+    g_switches.impl_side_painting_enabled_ = true;
 #else
-  return true;
+    g_switches.impl_side_painting_enabled_ = false;
 #endif
+  }
+
+  // Map-Image.
+  if (command_line.HasSwitch(cc::switches::kDisableMapImage))
+    g_switches.map_image_enabled_ = false;
+  else if (command_line.HasSwitch(cc::switches::kEnableMapImage))
+    g_switches.map_image_enabled_ = true;
+  else
+    g_switches.map_image_enabled_ = false;
+
+  // LCD-Text.
+  if (command_line.HasSwitch(cc::switches::kDisableLCDText)) {
+    g_switches.lcd_text_enabled_ = false;
+  } else if (command_line.HasSwitch(cc::switches::kEnableLCDText)) {
+    g_switches.lcd_text_enabled_ = true;
+  } else {
+#if defined(OS_ANDROID)
+    g_switches.lcd_text_enabled_ = false;
+#else
+    g_switches.lcd_text_enabled_ = true;
+#endif
+  }
+
+  g_switches.has_initialized_switches_ = true;
 }
 
-namespace {
-bool CheckImplSidePaintingStatus() {
-  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
-
-  if (command_line.HasSwitch(cc::switches::kDisableImplSidePainting))
-    return false;
-  else if (command_line.HasSwitch(cc::switches::kEnableImplSidePainting))
-    return true;
-
-#if defined(OS_ANDROID)
-  return true;
-#else
-  return false;
-#endif
-}
-}  // namespace
-
 bool IsImplSidePaintingEnabled() {
-  static bool enabled = CheckImplSidePaintingStatus();
-  return enabled;
+  InitializeSwitchesIfRequired();
+  return g_switches.impl_side_painting_enabled_;
 }
 
 bool IsMapImageEnabled() {
-  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+  InitializeSwitchesIfRequired();
+  return g_switches.map_image_enabled_;
+}
 
-  if (command_line.HasSwitch(cc::switches::kDisableMapImage))
-    return false;
-  else if (command_line.HasSwitch(cc::switches::kEnableMapImage))
-    return true;
-
-  return false;
+bool IsLCDTextEnabled() {
+  InitializeSwitchesIfRequired();
+  return g_switches.lcd_text_enabled_;
 }
 
 }  // namespace switches
 }  // namespace cc