fix multithread related crashes in skpdiff

tools/skpdiff/SkDifferentPixelsMetric_opencl.cpp

Index: tools/skpdiff/SkDifferentPixelsMetric_opencl.cpp
diff --git a/tools/skpdiff/SkDifferentPixelsMetric_opencl.cpp b/tools/skpdiff/SkDifferentPixelsMetric_opencl.cpp
index b3f5d2d7e0b00c70fb813e5b73ca4df3b5b9430d..14225055f1578c11353f15b99435be6e11cd21a4 100644
--- a/tools/skpdiff/SkDifferentPixelsMetric_opencl.cpp
+++ b/tools/skpdiff/SkDifferentPixelsMetric_opencl.cpp
@@ -18,7 +18,7 @@ static const char kDifferentPixelsKernelSource[] =
     "                             CLK_FILTER_NEAREST;                           \n"
     "                                                                           \n"
     "__kernel void diff(read_only image2d_t baseline, read_only image2d_t test, \n"
-    "                   __global int* result, __global int2* poi) {             \n"
+    "                   __global int* result) {                                 \n"
     "    int2 coord = (int2)(get_global_id(0), get_global_id(1));               \n"
     "    uint4 baselinePixel = read_imageui(baseline, gInSampler, coord);       \n"
     "    uint4 testPixel = read_imageui(test, gInSampler, coord);               \n"
@@ -27,78 +27,59 @@ static const char kDifferentPixelsKernelSource[] =
     "        baselinePixel.z != testPixel.z ||                                  \n"
     "        baselinePixel.w != testPixel.w) {                                  \n"
     "                                                                           \n"
-    "        int poiIndex = atomic_inc(result);                                 \n"
-    "        poi[poiIndex] = coord;                                             \n"
+    "        atomic_inc(result);                                                \n"
+    "        // TODO: generate alpha mask                                       \n"
     "    }                                                                      \n"
     "}                                                                          \n";
 
-struct SkDifferentPixelsMetric::QueuedDiff {
-    bool finished;
-    double result;
-    int numDiffPixels;
-    SkIPoint* poi;
-    cl_mem baseline;
-    cl_mem test;
-    cl_mem resultsBuffer;
-    cl_mem poiBuffer;
-};
-
-const char* SkDifferentPixelsMetric::getName() {
+const char* SkDifferentPixelsMetric::getName() const {
     return "different_pixels";
 }
 
-bool SkDifferentPixelsMetric::enablePOIAlphaMask() {
-    return false;
-}
-
-int SkDifferentPixelsMetric::queueDiff(SkBitmap* baseline, SkBitmap* test) {
-    int diffID = fQueuedDiffs.count();
+bool SkDifferentPixelsMetric::diff(SkBitmap* baseline, SkBitmap* test, bool computeMask,
+                                   Result* result) const {
     double startTime = get_seconds();
-    QueuedDiff* diff = fQueuedDiffs.push();
+
+    if (!fIsGood) {
+        return false;
+    }
 
     // If we never end up running the kernel, include some safe defaults in the result.
-    diff->finished = false;
-    diff->result = -1.0;
-    diff->numDiffPixels = 0;
-    diff->poi = NULL;
+    result->poiCount = 0;
 
     // Ensure the images are comparable
     if (baseline->width() != test->width() || baseline->height() != test->height() ||
         baseline->width() <= 0 || baseline->height() <= 0 ||
         baseline->config() != test->config()) {
-        diff->finished = true;
-        return diffID;
+        return false;
     }
 
+    cl_mem baselineImage;
+    cl_mem testImage;
+    cl_mem resultsBuffer;
+
     // Upload images to the CL device
-    if (!this->makeImage2D(baseline, &diff->baseline) || !this->makeImage2D(test, &diff->test)) {
-        diff->finished = true;
-        fIsGood = false;
-        return -1;
+    if (!this->makeImage2D(baseline, &baselineImage) || !this->makeImage2D(test, &testImage)) {
+        SkDebugf("creation of openCL images failed");
+        return false;
     }
 
     // A small hack that makes calculating percentage difference easier later on.
-    diff->result = 1.0 / ((double)baseline->width() * baseline->height());
+    result->result = 1.0 / ((double)baseline->width() * baseline->height());
 
     // Make a buffer to store results into. It must be initialized with pointers to memory.
     static const int kZero = 0;
     // We know OpenCL won't write to it because we use CL_MEM_COPY_HOST_PTR
-    diff->resultsBuffer = clCreateBuffer(fContext, CL_MEM_READ_WRITE | CL_MEM_COPY_HOST_PTR,
-                                         sizeof(int), (int*)&kZero, NULL);
-
-    diff->poiBuffer = clCreateBuffer(fContext, CL_MEM_WRITE_ONLY,
-                                     sizeof(int) * 2 * baseline->width() * baseline->height(),
-                                     NULL, NULL);
+    resultsBuffer = clCreateBuffer(fContext, CL_MEM_READ_WRITE | CL_MEM_COPY_HOST_PTR,
+                                   sizeof(int), (int*)&kZero, NULL);
 
     // Set all kernel arguments
-    cl_int setArgErr = clSetKernelArg(fKernel, 0, sizeof(cl_mem), &diff->baseline);
-    setArgErr       |= clSetKernelArg(fKernel, 1, sizeof(cl_mem), &diff->test);
-    setArgErr       |= clSetKernelArg(fKernel, 2, sizeof(cl_mem), &diff->resultsBuffer);
-    setArgErr       |= clSetKernelArg(fKernel, 3, sizeof(cl_mem), &diff->poiBuffer);
+    cl_int setArgErr = clSetKernelArg(fKernel, 0, sizeof(cl_mem), &baselineImage);
+    setArgErr       |= clSetKernelArg(fKernel, 1, sizeof(cl_mem), &testImage);
+    setArgErr       |= clSetKernelArg(fKernel, 2, sizeof(cl_mem), &resultsBuffer);
     if (CL_SUCCESS != setArgErr) {
         SkDebugf("Set arg failed: %s\n", cl_error_to_string(setArgErr));
-        fIsGood = false;
-        return -1;
+        return false;
     }
 
     // Queue this diff on the CL device
@@ -109,60 +90,25 @@ int SkDifferentPixelsMetric::queueDiff(SkBitmap* baseline, SkBitmap* test) {
                                         NULL, 0, NULL, &event);
     if (CL_SUCCESS != enqueueErr) {
         SkDebugf("Enqueue failed: %s\n", cl_error_to_string(enqueueErr));
-        fIsGood = false;
-        return -1;
+        return false;
     }
 
     // This makes things totally synchronous. Actual queue is not ready yet
     clWaitForEvents(1, &event);
-    diff->finished = true;
 
     // Immediate read back the results
-    clEnqueueReadBuffer(fCommandQueue, diff->resultsBuffer, CL_TRUE, 0,
-                        sizeof(int), &diff->numDiffPixels, 0, NULL, NULL);
-    diff->result *= (double)diff->numDiffPixels;
-    diff->result = (1.0 - diff->result);
-
-    // Reading a buffer of size zero can cause issues on some (Mac) OpenCL platforms.
-    if (diff->numDiffPixels > 0) {
-        diff->poi = SkNEW_ARRAY(SkIPoint, diff->numDiffPixels);
-        clEnqueueReadBuffer(fCommandQueue, diff->poiBuffer, CL_TRUE, 0,
-                        sizeof(SkIPoint) * diff->numDiffPixels, diff->poi, 0, NULL, NULL);
-    }
+    clEnqueueReadBuffer(fCommandQueue, resultsBuffer, CL_TRUE, 0,
+                        sizeof(int), &result->poiCount, 0, NULL, NULL);
+    result->result *= (double)result->poiCount;
+    result->result = (1.0 - result->result);
 
     // Release all the buffers created
-    clReleaseMemObject(diff->poiBuffer);
-    clReleaseMemObject(diff->resultsBuffer);
-    clReleaseMemObject(diff->baseline);
-    clReleaseMemObject(diff->test);
-
-    SkDebugf("Time: %f\n", (get_seconds() - startTime));
-
-    return diffID;
-}
-
-void SkDifferentPixelsMetric::deleteDiff(int id) {
-    QueuedDiff* diff = &fQueuedDiffs[id];
-    if (NULL != diff->poi) {
-        SkDELETE_ARRAY(diff->poi);
-        diff->poi = NULL;
-    }
-}
+    clReleaseMemObject(resultsBuffer);
+    clReleaseMemObject(baselineImage);
+    clReleaseMemObject(testImage);
 
-bool SkDifferentPixelsMetric::isFinished(int id) {
-    return fQueuedDiffs[id].finished;
-}
-
-double SkDifferentPixelsMetric::getResult(int id) {
-    return fQueuedDiffs[id].result;
-}
-
-int SkDifferentPixelsMetric::getPointsOfInterestCount(int id) {
-    return fQueuedDiffs[id].numDiffPixels;
-}
-
-SkIPoint* SkDifferentPixelsMetric::getPointsOfInterest(int id) {
-    return fQueuedDiffs[id].poi;
+    result->timeElapsed = get_seconds() - startTime;
+    return true;
 }
 
 bool SkDifferentPixelsMetric::onInit() {