Fix race condition in parallel font initialization.

src/ports/SkFontConfigInterface_direct.cpp

 /*
  * Copyright 2009 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /* migrated from chrome/src/skia/ext/SkFontHost_fontconfig_direct.cpp */
 
 #include <string>
@@ skipping 106 matching lines @@
     // new APIs
     virtual SkDataTable* getFamilyNames() SK_OVERRIDE;
     virtual bool matchFamilySet(const char inFamilyName[],
                                 SkString* outFamilyName,
                                 SkTArray<FontIdentity>*) SK_OVERRIDE;
 
 private:
     SkMutex mutex_;
 };
 
-SkFontConfigInterface* SkFontConfigInterface::GetSingletonDirectInterface() {
+SkFontConfigInterface* SkFontConfigInterface::GetSingletonDirectInterface(SkBaseMutex& mutex) {
+    SkAutoMutexAcquire ac(mutex);
     SK_DECLARE_STATIC_LAZY_PTR(SkFontConfigInterfaceDirect, direct);

[mtklein, 2014/06/26 18:59:07]

Given the mutex lock, this can become simply

static SkFontConfigInterfaceDirect* singleton = NULL;
if (singleton == NULL) {
  singleton = SkNEW(SkFontConfigInterfaceDirect);
}
return singleton;

That is, if we're under a mutex, SkLazyPtr isn't needed.

The slightly more performant alternative is to do this:

static bool initialized = false;
static SkFontConfigInteface* singleton = NULL;
SkOnce(&initialized, &mutex, CreateDirect, &singleton);
return singleton;

where CreateDirect is something like

/*static*/
void SkFontConfigInterface::CreateDirect(SkFontConfigInterface** ptr) {
  *ptr = SkNEW(SkFontConfigInterfaceDirect);
}

[tomhudson, 2014/06/26 21:01:52]

SK_DECLARE_STATIC_LAZY_PTR does nicely describe what we're doing.
I didn't want to introduce the extra CreateDirect() function, so implemented
your slightly-less-performant version.

Done

     return direct.get();
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 // Returns the string from the pattern, or NULL
 static const char* get_name(FcPattern* pattern, const char field[],
                             int index = 0) {
     const char* name;
     if (FcPatternGetString(pattern, field, index,
@@ skipping 581 matching lines @@
                 *trimmedMatches.append() = match[i];
             }
         }
 
         SkFontStyleSet_FC* sset = SkNEW_ARGS(SkFontStyleSet_FC,
                                              (trimmedMatches.begin(),
                                               trimmedMatches.count()));
 #endif
     return false;
 }