Make SkColorTable explicitly thread-safe.

include/core/SkColorTable.h

 
 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkColorTable_DEFINED
 #define SkColorTable_DEFINED
 
 #include "SkColor.h"
 #include "SkFlattenable.h"
 #include "SkImageInfo.h"
+#include "SkLazyPtr.h"
 
 /** \class SkColorTable
 
     SkColorTable holds an array SkPMColors (premultiplied 32-bit colors) used by
     8-bit bitmaps, where the bitmap bytes are interpreted as indices into the colortable.
+
+    SkColorTable is thread-safe.
 */
 class SK_API SkColorTable : public SkRefCnt {
 public:
     SK_DECLARE_INST_COUNT(SkColorTable)
 
-    /** Makes a deep copy of colors.
-     */
-    SkColorTable(const SkColorTable& src);
     SkColorTable(const SkPMColor colors[], int count);
     virtual ~SkColorTable();
 
     /** Returns the number of colors in the table.
      */
     int count() const { return fCount; }
 
     /** Returns the specified color from the table. In the debug build, this asserts that
      *  the index is in range (0 <= index < count).
      */
     SkPMColor operator[](int index) const {
         SkASSERT(fColors != NULL && (unsigned)index < (unsigned)fCount);
         return fColors[index];
     }
 
-    // TODO: Would making the read() methods const allow us to avoid copies?
-
     /** Return the array of colors for reading.
      */
-    const SkPMColor* readColors() { return fColors; }
+    const SkPMColor* readColors() const { return fColors; }
 
     /** read16BitCache() returns the array of RGB16 colors that mirror the 32bit colors.
      */
-    const uint16_t* read16BitCache();
+    const uint16_t* read16BitCache() const;
 
     explicit SkColorTable(SkReadBuffer&);
     void writeToBuffer(SkWriteBuffer&) const;
 
 private:
-    SkPMColor*  fColors;
-    uint16_t*   f16BitCache;
-    int         fCount;
+    static void Free16BitCache(uint16_t* cache) { sk_free(cache); }
+
+    SkPMColor*                          fColors;
+    SkLazyPtr<uint16_t, Free16BitCache> f16BitCache;
+    int                                 fCount;

[reed1, 2014/12/02 17:46:31]

can we make fColors and fCount const?

[mtklein, 2014/12/02 17:51:18]

Maybe, but it'll be an awkward enough rewrite of SkColorTable.cpp I'd want to
follow up.

The ugliest part is that it's sk_free(void*), not sk_free(const void*).  That's
actually all that prevents us from making f16BitCache const too.

 
     void init(const SkPMColor* colors, int count);
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif