Avoid too small reads to bufferMoreData()

src/codec/SkRawCodec.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodec.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 249 matching lines @@
             return SkStreamCopy(&fStreamBuffer, fStream.get());
         }
 
         if (newSize <= fStreamBuffer.bytesWritten()) {  // already buffered to newSize
             return true;
         }
         if (fWholeStreamRead) {  // newSize is larger than the whole stream.
             return false;
         }
 
-        const size_t sizeToRead = newSize - fStreamBuffer.bytesWritten();
-        SkAutoTMalloc<uint8> tempBuffer(sizeToRead);
+        // Try to read at least 8192 bytes to avoid to many small reads.
+        const size_t kMinSizeToRead = 8192;
+        const size_t sizeRequested = newSize - fStreamBuffer.bytesWritten();
+        const size_t sizeToRead = SkTMax(kMinSizeToRead, sizeRequested);
+        SkAutoSTMalloc<kMinSizeToRead, uint8> tempBuffer(sizeToRead);
         const size_t bytesRead = fStream->read(tempBuffer.get(), sizeToRead);
-        if (bytesRead != sizeToRead) {
+        if (bytesRead < sizeRequested) {
             return false;
         }
         return fStreamBuffer.write(tempBuffer.get(), bytesRead);
     }
 
     SkAutoTDelete<SkStream> fStream;
     bool fWholeStreamRead;
 
     SkDynamicMemoryWStream fStreamBuffer;
 
@@ skipping 147 matching lines @@
 };
 
 /*
  * Tries to handle the image with PIEX. If PIEX returns kOk and finds the preview image, create a
  * SkJpegCodec. If PIEX returns kFail, then the file is invalid, return nullptr. In other cases,
  * fallback to create SkRawCodec for DNG images.
  */
 SkCodec* SkRawCodec::NewFromStream(SkStream* stream) {
     SkAutoTDelete<SkRawStream> rawStream(new SkRawStream(stream));
     ::piex::PreviewImageData imageData;
-    // FIXME: ::piex::GetPreviewImageData() calls GetData() frequently with small amounts,
-    // resulting in many calls to bufferMoreData(). Could we make this more efficient by grouping
-    // smaller requests together?
     if (::piex::IsRaw(rawStream.get())) {
         ::piex::Error error = ::piex::GetPreviewImageData(rawStream.get(), &imageData);
 
         if (error == ::piex::Error::kOk && imageData.preview_length > 0) {
 #if !defined(GOOGLE3)
             // transferBuffer() is destructive to the rawStream. Abandon the rawStream after this
             // function call.
             // FIXME: one may avoid the copy of memoryStream and use the buffered rawStream.
             SkMemoryStream* memoryStream =
                     rawStream->transferBuffer(imageData.preview_offset, imageData.preview_length);
@@ skipping 105 matching lines @@
     SkISize sizeFloor = this->onGetScaledDimensions(1.f / std::floor(fullShortEdge / shortEdge));
     SkISize sizeCeil = this->onGetScaledDimensions(1.f / std::ceil(fullShortEdge / shortEdge));
     return sizeFloor == dim || sizeCeil == dim;
 }
 
 SkRawCodec::~SkRawCodec() {}
 
 SkRawCodec::SkRawCodec(SkDngImage* dngImage)
     : INHERITED(dngImage->getImageInfo(), nullptr)
     , fDngImage(dngImage) {}