fix multithread related crashes in skpdiff

tools/skpdiff/SkDiffContext.h

Index: tools/skpdiff/SkDiffContext.h
diff --git a/tools/skpdiff/SkDiffContext.h b/tools/skpdiff/SkDiffContext.h
index 20193b38514248e77ba6e7a34752cf299a413d14..e87f02f093d372fc9cd3f11663fa01f21ef6cce0 100644
--- a/tools/skpdiff/SkDiffContext.h
+++ b/tools/skpdiff/SkDiffContext.h
@@ -8,9 +8,11 @@
 #ifndef SkDiffContext_DEFINED
 #define SkDiffContext_DEFINED
 
+#include "SkThread.h"
 #include "SkString.h"
 #include "SkTArray.h"
 #include "SkTDArray.h"
+#include "SkTLList.h"
 
 class SkWStream;
 class SkImageDiffer;
@@ -110,13 +112,21 @@ private:
         SkString           fBaselinePath;
         SkString               fTestPath;
         SkTArray<DiffData>        fDiffs;
-        DiffRecord*                fNext;
     };
 
+    // This is needed to work around a bug in the multithreaded case where the
+    // image decoders are crashing when large numbers of threads are invoking
+    // the decoder at the same time.
+    SkMutex fImageMutex;

[scroggo, 2013/11/05 21:08:52]

Could you create a bug add a link to it here?

+
+    // Used to protect access to fRecords and ensure only one thread is
+    // adding new entries and/or iterating over the existing entries at a time
+    SkMutex fRecordMutex;
+
     // We use linked list for the records so that their pointers remain stable. A resizable array
     // might change its pointers, which would make it harder for async diffs to record their
     // results.
-    DiffRecord * fRecords;
+    SkTLList<DiffRecord> fRecords;
 
     SkImageDiffer** fDiffers;
     int fDifferCount;