unify pixelref and image ID space, so we can share IDs when we share pixels

src/core/SkPixelRef.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapCache.h"
 #include "SkMutex.h"
 #include "SkPixelRef.h"
@@ skipping 41 matching lines @@
 
     SkASSERT(SkIsPow2(PIXELREF_MUTEX_RING_COUNT));
 
     // atomic_inc might be overkill here. It may be fine if once in a while
     // we hit a race-condition and two subsequent calls get the same index...
     int index = sk_atomic_inc(&gPixelRefMutexRingIndex);
     return &gPixelRefMutexRing[index & (PIXELREF_MUTEX_RING_COUNT - 1)];
 }
 
 ///////////////////////////////////////////////////////////////////////////////
+#include "SkNextID.h"
 
-static uint32_t next_gen_id() {
-    static uint32_t gNextGenID = 0;
-    uint32_t genID;
+uint32_t SkNextID::ImageID() {
+    static uint32_t gID = 0;
+    uint32_t id;
     // Loop in case our global wraps around, as we never want to return a 0.
     do {
-        genID = sk_atomic_fetch_add(&gNextGenID, 2u) + 2;  // Never set the low bit.
-    } while (0 == genID);
-    return genID;
+        id = sk_atomic_fetch_add(&gID, 2u) + 2;  // Never set the low bit.
+    } while (0 == id);
+    return id;
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 void SkPixelRef::setMutex(SkBaseMutex* mutex) {
     if (NULL == mutex) {
         mutex = get_default_mutex();
     }
     fMutex = mutex;
 }
@@ skipping 212 matching lines @@
     return this->onLockPixelsAreWritable();
 }
 
 bool SkPixelRef::onLockPixelsAreWritable() const {
     return true;
 }
 
 uint32_t SkPixelRef::getGenerationID() const {
     uint32_t id = fTaggedGenID.load();
     if (0 == id) {
-        uint32_t next = next_gen_id() | 1u;
+        uint32_t next = SkNextID::ImageID() | 1u;
         if (fTaggedGenID.compare_exchange(&id, next)) {
             id = next;  // There was no race or we won the race.  fTaggedGenID is next now.
         } else {
             // We lost a race to set fTaggedGenID. compare_exchange() filled id with the winner.
         }
         // We can't quite SkASSERT(this->genIDIsUnique()). It could be non-unique
         // if we got here via the else path (pretty unlikely, but possible).
     }
     return id & ~1u;  // Mask off bottom unique bit.
 }
@@ skipping 90 matching lines @@
     }
 
     result->fUnlockProc = unlock_legacy_result;
     result->fUnlockContext = SkRef(this);   // this is balanced in our fUnlockProc
     result->fCTable = fRec.fColorTable;
     result->fPixels = fRec.fPixels;
     result->fRowBytes = fRec.fRowBytes;
     result->fSize.set(fInfo.width(), fInfo.height());
     return true;
 }