Destroy SkScanlineDecoder in the SkCodec subclass destructors

src/codec/SkJpegCodec.cpp

Index: src/codec/SkJpegCodec.cpp
diff --git a/src/codec/SkJpegCodec.cpp b/src/codec/SkJpegCodec.cpp
index 2eaff1a9a67f47be24d70c6e7dddba21fd056350..9c9bd77c13515ff17f32e2cf33bede895e7463f7 100644
--- a/src/codec/SkJpegCodec.cpp
+++ b/src/codec/SkJpegCodec.cpp
@@ -297,9 +297,15 @@ SkCodec::Result SkJpegCodec::onGetPixels(const SkImageInfo& dstInfo,
                                          void* dst, size_t dstRowBytes,
                                          const Options& options, SkPMColor*, int*) {
 
+    // Do not allow a regular decode if the caller has asked for a scanline decoder
+    if (NULL != this->scanlineDecoder()) {
+        return fDecoderMgr->returnFailure("cannot getPixels() if a scanline decoder has been"
+                "created", kInvalidParameters);
+    }
+
     // Rewind the stream if needed
     if (!this->handleRewind()) {
-        fDecoderMgr->returnFailure("could not rewind stream", kCouldNotRewind);
+        return fDecoderMgr->returnFailure("could not rewind stream", kCouldNotRewind);
     }
 
     // Get a pointer to the decompress info since we will use it quite frequently
@@ -388,6 +394,25 @@ SkCodec::Result SkJpegCodec::onGetPixels(const SkImageInfo& dstInfo,
 }
 
 /*
+ * We override the destructor to ensure that the scanline decoder is left in a
+ * finished state before destroying the decode manager.
+ */
+SkJpegCodec::~SkJpegCodec() {
+    SkAutoTDelete<SkScanlineDecoder> decoder(this->detachScanlineDecoder());
+    if (NULL != decoder) {
+        if (setjmp(fDecoderMgr->getJmpBuf())) {
+            SkCodecPrintf("setjmp: Error in libjpeg finish_decompress\n");

[scroggo, 2015/06/30 20:59:58]

Do we need this error message? I guess it could be a sign of a deeper problem,
but it seems like we have already decoded the image?

[msarett, 2015/06/30 21:33:00]

I would lean towards keeping it.  It doesn't print under default settings, and
I'd like to be warned if somehow we aren't using the jpeg library properly.  We
may not care, but I'd like to know something is "wrong" and make sure it's not
really wrong.

That said this is not a huge issue and if you feel more strongly than me, I'll
drop it :).

+            return;
+        }
+
+        // We may not have decoded the entire image.  Prevent libjpeg-turbo from failing on a
+        // partial decode.
+        fDecoderMgr->dinfo()->output_scanline = this->getInfo().height();
+        jpeg_finish_decompress(fDecoderMgr->dinfo());
+    }
+}
+
+/*
  * Enable scanline decoding for jpegs
  */
 class SkJpegScanlineDecoder : public SkScanlineDecoder {
@@ -443,15 +468,6 @@ public:
         return SkImageGenerator::kSuccess;
     }
 
-    void onFinish() override {
-        if (setjmp(fCodec->fDecoderMgr->getJmpBuf())) {
-            SkCodecPrintf("setjmp: Error in libjpeg finish_decompress\n");
-            return;
-        }
-
-        jpeg_finish_decompress(fCodec->fDecoderMgr->dinfo());
-    }
-
 private:
     SkJpegCodec*        fCodec;     // unowned
     SkAutoMalloc        fStorage;