fix multithread related crashes in skpdiff

tools/skpdiff/SkDiffContext.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmap.h"
 #include "SkImageDecoder.h"
 #include "SkOSFile.h"
 #include "SkRunnable.h"
 #include "SkStream.h"
 #include "SkTDict.h"
 #include "SkThreadPool.h"
 
 #include "SkDiffContext.h"
 #include "SkImageDiffer.h"
 #include "skpdiff_util.h"
 
 // Truncates the number of points of interests in JSON output to not freeze the parser
 static const int kMaxPOI = 100;
 
 SkDiffContext::SkDiffContext() {
-    fRecords = NULL;
     fDiffers = NULL;
     fDifferCount = 0;
     fThreadCount = SkThreadPool::kThreadPerCore;
 }
 
 SkDiffContext::~SkDiffContext() {
-    // Delete the record linked list
-    DiffRecord* currentRecord = fRecords;
-    while (NULL != currentRecord) {
-        DiffRecord* nextRecord = currentRecord->fNext;
-        SkDELETE(currentRecord);
-        currentRecord = nextRecord;
-    }
-
     if (NULL != fDiffers) {
         SkDELETE_ARRAY(fDiffers);
     }
 }
 
 void SkDiffContext::setDiffers(const SkTDArray<SkImageDiffer*>& differs) {
     // Delete whatever the last array of differs was
     if (NULL != fDiffers) {
         SkDELETE_ARRAY(fDiffers);
         fDiffers = NULL;
         fDifferCount = 0;
     }
 
     // Copy over the new differs
     fDifferCount = differs.count();
     fDiffers = SkNEW_ARRAY(SkImageDiffer*, fDifferCount);
     differs.copy(fDiffers);
 }
 
 void SkDiffContext::addDiff(const char* baselinePath, const char* testPath) {
     // Load the images at the paths
     SkBitmap baselineBitmap;
     SkBitmap testBitmap;
+    SkAutoMutexAcquire imageLock(fImageMutex);

[mtklein, 2013/11/06 14:24:36]

Put these in a {} block or just call .lock()?  It's sort of suggesting the wrong
thing to use an SkAutoMutexAcquire then unconditionally call release() later.

[djsollen, 2013/11/06 15:01:58]

The auto acquire is nice as it handles the cleanup in the event that we hit one
of the return statements.

[mtklein, 2013/11/06 15:09:41]

Ah.  Brain fart.  LGTM

     if (!SkImageDecoder::DecodeFile(baselinePath, &baselineBitmap)) {

[mtklein, 2013/11/06 14:24:36]

Does this bottleneck you now?  Is there a way to instantiate your own image
decoders instead of using the globals?

[djsollen, 2013/11/06 15:01:58]

I'm sure it bottlenecks the process a little, but I don't know how much faster
it could be because it crashes when decoding in parallel.  I could spend the
time to estimate what that cost is but I didn't want to add that to this CL,
which is why I filed the other bug.

         SkDebugf("Failed to load bitmap \"%s\"\n", baselinePath);
         return;
     }
     if (!SkImageDecoder::DecodeFile(testPath, &testBitmap)) {
         SkDebugf("Failed to load bitmap \"%s\"\n", testPath);
         return;
     }
+    imageLock.release();
 
     // Setup a record for this diff
-    DiffRecord* newRecord = SkNEW(DiffRecord);
+    SkAutoMutexAcquire recordsLock(fRecordMutex);
+    DiffRecord* newRecord = fRecords.addToHead(DiffRecord());
     newRecord->fBaselinePath = baselinePath;
     newRecord->fTestPath = testPath;
-    newRecord->fNext = fRecords;
-    fRecords = newRecord;
+    recordsLock.release();
 
     // Perform each diff
     for (int differIndex = 0; differIndex < fDifferCount; differIndex++) {
         SkImageDiffer* differ = fDiffers[differIndex];
         int diffID = differ->queueDiff(&baselineBitmap, &testBitmap);
         if (diffID >= 0) {
 
             // Copy the results into data for this record
             DiffData& diffData = newRecord->fDiffs.push_back();
 
             diffData.fDiffName = differ->getName();
             diffData.fResult = differ->getResult(diffID);
 
             int poiCount = differ->getPointsOfInterestCount(diffID);
             SkIPoint* poi = differ->getPointsOfInterest(diffID);
             diffData.fPointsOfInterest.append(poiCount, poi);
 
             // Because we are doing everything synchronously for now, we are done with the diff
             // after reading it.
             differ->deleteDiff(diffID);
         }
     }
-
-    // if we get a difference and we want the alpha mask then compute it here.
 }
 
 class SkThreadedDiff : public SkRunnable {
 public:
     SkThreadedDiff() : fDiffContext(NULL) { }
 
     void setup(SkDiffContext* diffContext, const SkString& baselinePath, const SkString& testPath) {
         fDiffContext = diffContext;
         fBaselinePath = baselinePath;
         fTestPath = testPath;
@@ skipping 69 matching lines @@
 
     for (int x = 0; x < baselineEntries.count(); x++) {
         runnableDiffs[x].setup(this, baselineEntries[x], testEntries[x]);
         threadPool.add(&runnableDiffs[x]);
     }
 
     threadPool.wait();
 }
 
 void SkDiffContext::outputRecords(SkWStream& stream, bool useJSONP) {
-    DiffRecord* currentRecord = fRecords;
+    SkTLList<DiffRecord>::Iter iter(fRecords, SkTLList<DiffRecord>::Iter::kHead_IterStart);
+    DiffRecord* currentRecord = iter.get();
+
     if (useJSONP) {
         stream.writeText("var SkPDiffRecords = {\n");
     } else {
         stream.writeText("{\n");
     }
     stream.writeText("    \"records\": [\n");
     while (NULL != currentRecord) {
         stream.writeText("        {\n");
 
             SkString differenceAbsPath = get_absolute_path(currentRecord->fDifferencePath);
@@ skipping 62 matching lines @@
                 // JSON does not allow trailing commas
                 if (diffIndex + 1 < currentRecord->fDiffs.count()) {
                     stream.writeText(",");
                 }
                 stream.writeText("                \n");
             }
             stream.writeText("            ]\n");
 
         stream.writeText("        }");
 
+        currentRecord = iter.next();
+
         // JSON does not allow trailing commas
-        if (NULL != currentRecord->fNext) {
+        if (NULL != currentRecord) {
             stream.writeText(",");
         }
         stream.writeText("\n");
-        currentRecord = currentRecord->fNext;
     }
     stream.writeText("    ]\n");
     if (useJSONP) {
         stream.writeText("};\n");
     } else {
         stream.writeText("}\n");
     }
 }
 
 void SkDiffContext::outputCsv(SkWStream& stream) {
     SkTDict<int> columns(2);
     int cntColumns = 0;
 
     stream.writeText("key");
 
-    DiffRecord* currentRecord = fRecords;
+    SkTLList<DiffRecord>::Iter iter(fRecords, SkTLList<DiffRecord>::Iter::kHead_IterStart);
+    DiffRecord* currentRecord = iter.get();
 
     // Write CSV header and create a dictionary of all columns.
     while (NULL != currentRecord) {
         for (int diffIndex = 0; diffIndex < currentRecord->fDiffs.count(); diffIndex++) {
             DiffData& data = currentRecord->fDiffs[diffIndex];
             if (!columns.find(data.fDiffName)) {
                 columns.set(data.fDiffName, cntColumns);
                 stream.writeText(", ");
                 stream.writeText(data.fDiffName);
                 cntColumns++;
             }
         }
-        currentRecord = currentRecord->fNext;
+        currentRecord = iter.next();
     }
     stream.writeText("\n");
 
     double values[100];
     SkASSERT(cntColumns < 100);  // Make the array larger, if we ever have so many diff types.
 
-    currentRecord = fRecords;
+    SkTLList<DiffRecord>::Iter iter2(fRecords, SkTLList<DiffRecord>::Iter::kHead_IterStart);
+    currentRecord = iter2.get();
     while (NULL != currentRecord) {
         for (int i = 0; i < cntColumns; i++) {
             values[i] = -1;
         }
 
         for (int diffIndex = 0; diffIndex < currentRecord->fDiffs.count(); diffIndex++) {
             DiffData& data = currentRecord->fDiffs[diffIndex];
             int index = -1;
             SkAssertResult(columns.find(data.fDiffName, &index));
             SkASSERT(index >= 0 && index < cntColumns);
             values[index] = data.fResult;
         }
 
         const char* filename = currentRecord->fBaselinePath.c_str() +
                 strlen(currentRecord->fBaselinePath.c_str()) - 1;
         while (filename > currentRecord->fBaselinePath.c_str() && *(filename - 1) != '/') {
             filename--;
         }
 
         stream.writeText(filename);
 
         for (int i = 0; i < cntColumns; i++) {
             SkString str;
             str.printf(", %f", values[i]);
             stream.writeText(str.c_str());
         }
         stream.writeText("\n");
 
-        currentRecord = currentRecord->fNext;
+        currentRecord = iter2.next();
     }
 }