Send SkPicture deletion message lazily.

src/core/SkPicture.cpp

 /*
  * Copyright 2007 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkPictureFlat.h"
 #include "SkPictureData.h"
 #include "SkPicturePlayback.h"
 #include "SkPictureRecord.h"
 #include "SkPictureRecorder.h"
 
+#include "SkAtomics.h"
 #include "SkBitmapDevice.h"
 #include "SkCanvas.h"
 #include "SkChunkAlloc.h"
 #include "SkMessageBus.h"
 #include "SkPaintPriv.h"
 #include "SkPathEffect.h"
 #include "SkPicture.h"
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkStream.h"
@@ skipping 14 matching lines @@
 #include "SkRecordDraw.h"
 #include "SkRecordOpts.h"
 #include "SkRecorder.h"
 
 DECLARE_SKMESSAGEBUS_MESSAGE(SkPicture::DeletionMessage);
 
 template <typename T> int SafeCount(const T* obj) {
     return obj ? obj->count() : 0;
 }
 
-static int32_t gPictureGenerationID;
-
-// never returns a 0
-static int32_t next_picture_generation_id() {
-    // Loop in case our global wraps around.
-    int32_t genID;
-    do {
-        genID = sk_atomic_inc(&gPictureGenerationID) + 1;
-    } while (0 == genID);
-    return genID;
-}
-
 ///////////////////////////////////////////////////////////////////////////////
 
 namespace {
 
 // Some commands have a paint, some have an optional paint.  Either way, get back a pointer.
 static const SkPaint* AsPtr(const SkPaint& p) { return &p; }
 static const SkPaint* AsPtr(const SkRecords::Optional<SkPaint>& p) { return p; }
 
 /** SkRecords visitor to determine whether an instance may require an
     "external" bitmap to rasterize. May return false positives.
@@ skipping 169 matching lines @@
                                                       int sampleCount) const {
     // TODO: the heuristic used here needs to be refined
     static const int kNumSlowPathsTol = 6;
 
     int numSlowPathDashedPaths = fNumPaintWithPathEffectUses;
     if (0 == sampleCount) {
         // The fast dashing path only works when MSAA is disabled
         numSlowPathDashedPaths -= fNumFastPathDashEffects;
     }
 
-    int numSlowPaths = fNumAAConcavePaths - 
+    int numSlowPaths = fNumAAConcavePaths -
                        fNumAAHairlineConcavePaths -
                        fNumAADFEligibleConcavePaths;
 
     bool ret = numSlowPathDashedPaths + numSlowPaths < kNumSlowPathsTol;
 
     if (!ret && reason) {
         *reason = "Too many slow paths (either concave or dashed).";
     }
     return ret;
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 int SkPicture::drawableCount() const {
     return fDrawablePicts.get() ? fDrawablePicts->count() : 0;
 }
 
 SkPicture const* const* SkPicture::drawablePicts() const {
     return fDrawablePicts.get() ? fDrawablePicts->begin() : NULL;
 }
 
 SkPicture::~SkPicture() {
-    SkPicture::DeletionMessage msg;
-    msg.fUniqueID = this->uniqueID();
-    SkMessageBus<SkPicture::DeletionMessage>::Post(msg);
+    // If the ID is still zero, no one has read it, so no need to send this message.
+    uint32_t id = sk_atomic_load(&fUniqueID, sk_memory_order_relaxed);
+    if (id != 0) {
+        SkPicture::DeletionMessage msg;
+        msg.fUniqueID = id;
+        SkMessageBus<SkPicture::DeletionMessage>::Post(msg);
+    }
 }
 
 void SkPicture::EXPERIMENTAL_addAccelData(const SkPicture::AccelData* data) const {
     fAccelData.reset(SkRef(data));
 }
 
 const SkPicture::AccelData* SkPicture::EXPERIMENTAL_getAccelData(
         SkPicture::AccelData::Key key) const {
     if (fAccelData.get() && fAccelData->getKey() == key) {
         return fAccelData.get();
@@ skipping 195 matching lines @@
     return fAnalysis.suitableForGpuRasterization(reason, 0);
 }
 #endif
 
 bool SkPicture::hasText()             const { return fAnalysis.fHasText; }
 bool SkPicture::willPlayBackBitmaps() const { return fAnalysis.fWillPlaybackBitmaps; }
 int  SkPicture::approximateOpCount()  const { return fRecord->count(); }
 
 SkPicture::SkPicture(const SkRect& cullRect, SkRecord* record, SnapshotArray* drawablePicts,
                      SkBBoxHierarchy* bbh)
-    : fUniqueID(next_picture_generation_id())
+    : fUniqueID(0)
     , fCullRect(cullRect)
     , fRecord(SkRef(record))
     , fBBH(SkSafeRef(bbh))
     , fDrawablePicts(drawablePicts)     // take ownership
     , fAnalysis(*fRecord)
 {}
+
+
+static uint32_t gNextID = 1;
+uint32_t SkPicture::uniqueID() const {
+    uint32_t id = sk_atomic_load(&fUniqueID, sk_memory_order_relaxed);
+    while (id == 0) {
+        uint32_t next = sk_atomic_fetch_add(&gNextID, 1u);
+        if (sk_atomic_compare_exchange(&fUniqueID, &id, next,
+                                       sk_memory_order_relaxed,
+                                       sk_memory_order_relaxed)) {
+            id = next;
+        } else {
+            // sk_atomic_compare_exchange replaced id with the current value of fUniqueID.
+        }
+    }
+    return id;
+}