SkOnce in is_lcd_supported instead of hand rolled double-checked locking.

BUG=skia:
R=bungeman@google.com, reed@google.com

Author: mtklein@google.com

Review URL: https://codereview.chromium.org/155963003

git-svn-id: http://skia.googlecode.com/svn/trunk@13387 2bbb7eff-a529-9590-31e7-b0007b416f81

include/core/SkOnce.h

@@ -40,8 +40,32 @@ struct SkOnceFlag;  // If manually created, initialize with SkOnceFlag once = SK
 template <typename Func, typename Arg>
 inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)() = NULL);
 
+// If you've already got a lock and a flag to use, this variant lets you avoid an extra SkOnceFlag.
+template <typename Lock, typename Func, typename Arg>
+inline void SkOnce(bool* done, Lock* lock, Func f, Arg arg, void(*atExit)() = NULL);
+
 //  ----------------------  Implementation details below here. -----------------------------
 
+// This is POD and must be zero-initialized.
+struct SkSpinlock {
+    void acquire() {
+        SkASSERT(shouldBeZero == 0);
+        // No memory barrier needed, but sk_atomic_cas gives us at least release anyway.
+        while (!sk_atomic_cas(&thisIsPrivate, 0, 1)) {
+            // spin
+        }
+    }
+
+    void release() {
+        SkASSERT(shouldBeZero == 0);
+        // This requires a release memory barrier before storing, which sk_atomic_cas guarantees.
+        SkAssertResult(sk_atomic_cas(&thisIsPrivate, 1, 0));
+    }
+
+    int32_t thisIsPrivate;
+    SkDEBUGCODE(int32_t shouldBeZero;)
+};
+
 struct SkOnceFlag {
     bool done;
     SkSpinlock lock;
@@ -87,6 +111,16 @@ inline static void acquire_barrier() {
     full_barrier_on_arm();
 }
 
+// Works with SkSpinlock or SkMutex.
+template <typename Lock>
+class SkAutoLockAcquire {
+public:
+    explicit SkAutoLockAcquire(Lock* lock) : fLock(lock) { fLock->acquire(); }
+    ~SkAutoLockAcquire() { fLock->release(); }
+private:
+    Lock* fLock;
+};
+
 // We've pulled a pretty standard double-checked locking implementation apart
 // into its main fast path and a slow path that's called when we suspect the
 // one-time code hasn't run yet.
@@ -94,10 +128,10 @@ inline static void acquire_barrier() {
 // This is the guts of the code, called when we suspect the one-time code hasn't been run yet.
 // This should be rarely called, so we separate it from SkOnce and don't mark it as inline.
 // (We don't mind if this is an actual function call, but odds are it'll be inlined anyway.)
-template <typename Func, typename Arg>
-static void sk_once_slow(SkOnceFlag* once, Func f, Arg arg, void (*atExit)()) {
-    const SkAutoSpinlock lock(&once->lock);
-    if (!once->done) {
+template <typename Lock, typename Func, typename Arg>
+static void sk_once_slow(bool* done, Lock* lock, Func f, Arg arg, void (*atExit)()) {
+    const SkAutoLockAcquire<Lock> locked(lock);
+    if (!*done) {
         f(arg);
         if (atExit != NULL) {
             atexit(atExit);
@@ -112,15 +146,15 @@ static void sk_once_slow(SkOnceFlag* once, Func f, Arg arg, void (*atExit)()) {
         // We'll use this in the fast path to make sure f(arg)'s effects are
         // observable whenever we observe *done == true.
         release_barrier();
-        once->done = true;
+        *done = true;
     }
 }
 
 // This is our fast path, called all the time.  We do really want it to be inlined.
-template <typename Func, typename Arg>
-inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)()) {
-    if (!SK_ANNOTATE_UNPROTECTED_READ(once->done)) {
-        sk_once_slow(once, f, arg, atExit);
+template <typename Lock, typename Func, typename Arg>
+inline void SkOnce(bool* done, Lock* lock, Func f, Arg arg, void(*atExit)()) {
+    if (!SK_ANNOTATE_UNPROTECTED_READ(*done)) {
+        sk_once_slow(done, lock, f, arg, atExit);
     }
     // Also known as a load-load/load-store barrier, this acquire barrier makes
     // sure that anything we read from memory---in particular, memory written by
@@ -135,6 +169,11 @@ inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)()) {
     acquire_barrier();
 }
 
+template <typename Func, typename Arg>
+inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)()) {
+    return SkOnce(&once->done, &once->lock, f, arg, atExit);
+}
+
 #undef SK_ANNOTATE_BENIGN_RACE
 
 #endif  // SkOnce_DEFINED

include/core/SkThread.h

@@ -51,35 +51,6 @@ static void sk_membar_acquire__after_atomic_conditional_inc();
 
 #include SK_ATOMICS_PLATFORM_H
 
-// This is POD and must be zero-initialized.
-struct SkSpinlock {
-    void acquire() {
-        SkASSERT(shouldBeZero == 0);
-        // No memory barrier needed, but sk_atomic_cas gives us at least release anyway.
-        while (!sk_atomic_cas(&thisIsPrivate, 0, 1)) {
-            // spin
-        }
-    }
-
-    void release() {
-        SkASSERT(shouldBeZero == 0);
-        // This requires a release memory barrier before storing, which sk_atomic_cas guarantees.
-        SkAssertResult(sk_atomic_cas(&thisIsPrivate, 1, 0));
-    }
-
-    int32_t thisIsPrivate;
-    SkDEBUGCODE(int32_t shouldBeZero;)
-};
-
-class SkAutoSpinlock : SkNoncopyable {
-public:
-    explicit SkAutoSpinlock(SkSpinlock* lock) : fLock(lock) { fLock->acquire(); }
-    ~SkAutoSpinlock() { fLock->release(); }
-private:
-    SkSpinlock* fLock;
-};
-#define SkAutoSpinlock(...) SK_REQUIRE_LOCAL_VAR(SkAutoSpinlock)
-
 /** SK_MUTEX_PLATFORM_H must provide the following (or equivalent) declarations.
 
 class SkBaseMutex {

src/ports/SkFontHost_FreeType.cpp

@@ -6,6 +6,7 @@
  * found in the LICENSE file.
  */
 
+#include "SkAdvancedTypefaceMetrics.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkColorPriv.h"
@@ -18,7 +19,7 @@
 #include "SkMask.h"
 #include "SkMaskGamma.h"
 #include "SkOTUtils.h"
-#include "SkAdvancedTypefaceMetrics.h"
+#include "SkOnce.h"
 #include "SkScalerContext.h"
 #include "SkStream.h"
 #include "SkString.h"
@@ -160,17 +161,22 @@ static bool InitFreetype() {
     return true;
 }
 
+// Called while holding gFTMutex.
+static void determine_lcd_support(bool* lcdSupported) {
+    if (!gLCDSupportValid) {
+        // This will determine LCD support as a side effect.
+        InitFreetype();
+        FT_Done_FreeType(gFTLibrary);
+    }
+    SkASSERT(gLCDSupportValid);
+    *lcdSupported = gLCDSupport;
+}
+
 // Lazy, once, wrapper to ask the FreeType Library if it can support LCD text
 static bool is_lcd_supported() {
-    if (!gLCDSupportValid) {
-        SkAutoMutexAcquire  ac(gFTMutex);
-
-        if (!gLCDSupportValid) {
-            InitFreetype();
-            FT_Done_FreeType(gFTLibrary);
-        }
-    }
-    return gLCDSupport;
+    static bool lcdSupported = false;
+    SkOnce(&gLCDSupportValid, &gFTMutex, determine_lcd_support, &lcdSupported);
+    return lcdSupported;
 }
 
 class SkScalerContext_FreeType : public SkScalerContext_FreeType_Base {