Add support for Uncompress(source, sink). Various changes to allow

Uncompress(source, sink) to get the same performance as the different variants of Uncompress to Cord/DataBuffer/String/FlatBuffer. Changes to efficiently support Uncompress(source, sink) -------- a) For strings - we add support to StringByteSink to do GetAppendBuffer so we can write to it without copying. b) For flat array buffers, we do GetAppendBuffer and see if we can get a full buffer. With the above changes we get performance with ByteSource/ByteSink that is very close to directly using flat arrays and strings. We add various benchmark cases to demonstrate that. Orthogonal change ------------------ Add support for TryFastAppend() for SnappyScatteredWriter. Benchmark results are below CPU: Intel Core2 dL1:32KB dL2:4096KB Benchmark Time(ns) CPU(ns) Iterations ----------------------------------------------------- BM_UFlat/0 109065 108996 6410 896.0MB/s html BM_UFlat/1 1012175 1012343 691 661.4MB/s urls BM_UFlat/2 26775 26771 26149 4.4GB/s jpg BM_UFlat/3 48947 48940 14363 1.8GB/s pdf BM_UFlat/4 441029 440835 1589 886.1MB/s html4 BM_UFlat/5 39861 39880 17823 588.3MB/s cp BM_UFlat/6 18315 18300 38126 581.1MB/s c BM_UFlat/7 5254 5254 100000 675.4MB/s lsp BM_UFlat/8 1568060 1567376 447 626.6MB/s xls BM_UFlat/9 337512 337734 2073 429.5MB/s txt1 BM_UFlat/10 287269 287054 2434 415.9MB/s txt2 BM_UFlat/11 890098 890219 787 457.2MB/s txt3 BM_UFlat/12 1186593 1186863 590 387.2MB/s txt4 BM_UFlat/13 573927 573318 1000 853.7MB/s bin BM_UFlat/14 64250 64294 10000 567.2MB/s sum BM_UFlat/15 7301 7300 96153 552.2MB/s man BM_UFlat/16 109617 109636 6375 1031.5MB/s pb BM_UFlat/17 364438 364497 1921 482.3MB/s gaviota BM_UFlatSink/0 108518 108465 6450 900.4MB/s html BM_UFlatSink/1 991952 991997 705 675.0MB/s urls BM_UFlatSink/2 26815 26798 26065 4.4GB/s jpg BM_UFlatSink/3 49127 49122 14255 1.8GB/s pdf BM_UFlatSink/4 436674 436731 1604 894.4MB/s html4 BM_UFlatSink/5 39738 39733 17345 590.5MB/s cp BM_UFlatSink/6 18413 18416 37962 577.4MB/s c BM_UFlatSink/7 5677 5676 100000 625.2MB/s lsp BM_UFlatSink/8 1552175 1551026 451 633.2MB/s xls BM_UFlatSink/9 338526 338489 2065 428.5MB/s txt1 BM_UFlatSink/10 289387 289307 2420 412.6MB/s txt2 BM_UFlatSink/11 893803 893706 783 455.4MB/s txt3 BM_UFlatSink/12 1195919 1195459 586 384.4MB/s txt4 BM_UFlatSink/13 559637 559779 1000 874.3MB/s bin BM_UFlatSink/14 65073 65094 10000 560.2MB/s sum BM_UFlatSink/15 7618 7614 92823 529.5MB/s man BM_UFlatSink/16 110085 110121 6352 1027.0MB/s pb BM_UFlatSink/17 369196 368915 1896 476.5MB/s gaviota BM_UValidate/0 46954 46957 14899 2.0GB/s html BM_UValidate/1 500621 500868 1000 1.3GB/s urls BM_UValidate/2 283 283 2481447 417.2GB/s jpg BM_UValidate/3 16230 16228 43137 5.4GB/s pdf BM_UValidate/4 189129 189193 3701 2.0GB/s html4 A=uday R=sanjay
2015-06-22 16:03:28 +02:00
parent b2ad960067
commit b2312c4c25
5 changed files with 420 additions and 1 deletions
--- a/snappy.cc
+++ b/snappy.cc
@@ -863,6 +863,7 @@ static bool InternalUncompressAllTags(SnappyDecompressor* decompressor,

  // Process the entire input
  decompressor->DecompressAllTags(writer);
+  writer->Flush();
  return (decompressor->eof() && writer->CheckLength());
 }

@@ -1115,6 +1116,7 @@ class SnappyIOVecWriter {
    return true;
  }

+  inline void Flush() {}
 };

 bool RawUncompressToIOVec(const char* compressed, size_t compressed_length,
@@ -1215,6 +1217,10 @@ class SnappyArrayWriter {
    op_ = op + len;
    return true;
  }
+  inline size_t Produced() const {
+    return op_ - base_;
+  }
+  inline void Flush() {}
 };

 bool RawUncompress(const char* compressed, size_t n, char* uncompressed) {
@@ -1269,6 +1275,7 @@ class SnappyDecompressionValidator {
    produced_ += len;
    return produced_ <= expected_;
  }
+  inline void Flush() {}
 };

 bool IsValidCompressedBuffer(const char* compressed, size_t n) {
@@ -1277,6 +1284,11 @@ bool IsValidCompressedBuffer(const char* compressed, size_t n) {
  return InternalUncompress(&reader, &writer);
 }

+bool IsValidCompressed(Source* compressed) {
+  SnappyDecompressionValidator writer;
+  return InternalUncompress(compressed, &writer);
+}
+
 void RawCompress(const char* input,
                 size_t input_length,
                 char* compressed,
@@ -1300,6 +1312,241 @@ size_t Compress(const char* input, size_t input_length, string* compressed) {
  return compressed_length;
 }

+// -----------------------------------------------------------------------
+// Sink interface
+// -----------------------------------------------------------------------
+
+// A type that decompresses into a Sink. The template parameter
+// Allocator must export one method "char* Allocate(int size);", which
+// allocates a buffer of "size" and appends that to the destination.
+template <typename Allocator>
+class SnappyScatteredWriter {
+  Allocator allocator_;
+
+  // We need random access into the data generated so far.  Therefore
+  // we keep track of all of the generated data as an array of blocks.
+  // All of the blocks except the last have length kBlockSize.
+  vector<char*> blocks_;
+  size_t expected_;
+
+  // Total size of all fully generated blocks so far
+  size_t full_size_;
+
+  // Pointer into current output block
+  char* op_base_;       // Base of output block
+  char* op_ptr_;        // Pointer to next unfilled byte in block
+  char* op_limit_;      // Pointer just past block
+
+  inline size_t Size() const {
+    return full_size_ + (op_ptr_ - op_base_);
+  }
+
+  bool SlowAppend(const char* ip, size_t len);
+  bool SlowAppendFromSelf(size_t offset, size_t len);
+
+ public:
+  inline explicit SnappyScatteredWriter(const Allocator& allocator)
+      : allocator_(allocator),
+        full_size_(0),
+        op_base_(NULL),
+        op_ptr_(NULL),
+        op_limit_(NULL) {
+  }
+
+  inline void SetExpectedLength(size_t len) {
+    assert(blocks_.empty());
+    expected_ = len;
+  }
+
+  inline bool CheckLength() const {
+    return Size() == expected_;
+  }
+
+  // Return the number of bytes actually uncompressed so far
+  inline size_t Produced() const {
+    return Size();
+  }
+
+  inline bool Append(const char* ip, size_t len) {
+    size_t avail = op_limit_ - op_ptr_;
+    if (len <= avail) {
+      // Fast path
+      memcpy(op_ptr_, ip, len);
+      op_ptr_ += len;
+      return true;
+    } else {
+      return SlowAppend(ip, len);
+    }
+  }
+
+  inline bool TryFastAppend(const char* ip, size_t available, size_t length) {
+    char* op = op_ptr_;
+    const int space_left = op_limit_ - op;
+    if (length <= 16 && available >= 16 + kMaximumTagLength &&
+        space_left >= 16) {
+      // Fast path, used for the majority (about 95%) of invocations.
+      UNALIGNED_STORE64(op, UNALIGNED_LOAD64(ip));
+      UNALIGNED_STORE64(op + 8, UNALIGNED_LOAD64(ip + 8));
+      op_ptr_ = op + length;
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  inline bool AppendFromSelf(size_t offset, size_t len) {
+    // See SnappyArrayWriter::AppendFromSelf for an explanation of
+    // the "offset - 1u" trick.
+    if (offset - 1u < op_ptr_ - op_base_) {
+      const size_t space_left = op_limit_ - op_ptr_;
+      if (space_left >= len + kMaxIncrementCopyOverflow) {
+        // Fast path: src and dst in current block.
+        IncrementalCopyFastPath(op_ptr_ - offset, op_ptr_, len);
+        op_ptr_ += len;
+        return true;
+      }
+    }
+    return SlowAppendFromSelf(offset, len);
+  }
+
+  // Called at the end of the decompress. We ask the allocator
+  // write all blocks to the sink.
+  inline void Flush() { allocator_.Flush(Produced()); }
+};
+
+template<typename Allocator>
+bool SnappyScatteredWriter<Allocator>::SlowAppend(const char* ip, size_t len) {
+  size_t avail = op_limit_ - op_ptr_;
+  while (len > avail) {
+    // Completely fill this block
+    memcpy(op_ptr_, ip, avail);
+    op_ptr_ += avail;
+    assert(op_limit_ - op_ptr_ == 0);
+    full_size_ += (op_ptr_ - op_base_);
+    len -= avail;
+    ip += avail;
+
+    // Bounds check
+    if (full_size_ + len > expected_) {
+      return false;
+    }
+
+    // Make new block
+    size_t bsize = min<size_t>(kBlockSize, expected_ - full_size_);
+    op_base_ = allocator_.Allocate(bsize);
+    op_ptr_ = op_base_;
+    op_limit_ = op_base_ + bsize;
+    blocks_.push_back(op_base_);
+    avail = bsize;
+  }
+
+  memcpy(op_ptr_, ip, len);
+  op_ptr_ += len;
+  return true;
+}
+
+template<typename Allocator>
+bool SnappyScatteredWriter<Allocator>::SlowAppendFromSelf(size_t offset,
+                                                         size_t len) {
+  // Overflow check
+  // See SnappyArrayWriter::AppendFromSelf for an explanation of
+  // the "offset - 1u" trick.
+  const size_t cur = Size();
+  if (offset - 1u >= cur) return false;
+  if (expected_ - cur < len) return false;
+
+  // Currently we shouldn't ever hit this path because Compress() chops the
+  // input into blocks and does not create cross-block copies. However, it is
+  // nice if we do not rely on that, since we can get better compression if we
+  // allow cross-block copies and thus might want to change the compressor in
+  // the future.
+  size_t src = cur - offset;
+  while (len-- > 0) {
+    char c = blocks_[src >> kBlockLog][src & (kBlockSize-1)];
+    Append(&c, 1);
+    src++;
+  }
+  return true;
+}
+
+class SnappySinkAllocator {
+ public:
+  explicit SnappySinkAllocator(Sink* dest): dest_(dest) {}
+  ~SnappySinkAllocator() {}
+
+  char* Allocate(int size) {
+    Datablock block(new char[size], size);
+    blocks_.push_back(block);
+    return block.data;
+  }
+
+  // We flush only at the end, because the writer wants
+  // random access to the blocks and once we hand the
+  // block over to the sink, we can't access it anymore.
+  // Also we don't write more than has been actually written
+  // to the blocks.
+  void Flush(size_t size) {
+    size_t size_written = 0;
+    size_t block_size;
+    for (int i = 0; i < blocks_.size(); ++i) {
+      block_size = min<size_t>(blocks_[i].size, size - size_written);
+      dest_->AppendAndTakeOwnership(blocks_[i].data, block_size,
+                                    &SnappySinkAllocator::Deleter, NULL);
+      size_written += block_size;
+    }
+    blocks_.clear();
+  }
+
+ private:
+  struct Datablock {
+    char* data;
+    size_t size;
+    Datablock(char* p, size_t s) : data(p), size(s) {}
+  };
+
+  static void Deleter(void* arg, const char* bytes, size_t size) {
+    delete[] bytes;
+  }
+
+  Sink* dest_;
+  vector<Datablock> blocks_;
+
+  // Note: copying this object is allowed
+};
+
+size_t UncompressAsMuchAsPossible(Source* compressed, Sink* uncompressed) {
+  SnappySinkAllocator allocator(uncompressed);
+  SnappyScatteredWriter<SnappySinkAllocator> writer(allocator);
+  InternalUncompress(compressed, &writer);
+  return writer.Produced();
+}
+
+bool Uncompress(Source* compressed, Sink* uncompressed) {
+  // Read the uncompressed length from the front of the compressed input
+  SnappyDecompressor decompressor(compressed);
+  uint32 uncompressed_len = 0;
+  if (!decompressor.ReadUncompressedLength(&uncompressed_len)) {
+    return false;
+  }
+
+  char c;
+  size_t allocated_size;
+  char* buf = uncompressed->GetAppendBufferVariable(
+      1, uncompressed_len, &c, 1, &allocated_size);
+
+  // If we can get a flat buffer, then use it, otherwise do block by block
+  // uncompression
+  if (allocated_size >= uncompressed_len) {
+    SnappyArrayWriter writer(buf);
+    bool result = InternalUncompressAllTags(
+        &decompressor, &writer, uncompressed_len);
+    uncompressed->Append(buf, writer.Produced());
+    return result;
+  } else {
+    SnappySinkAllocator allocator(uncompressed);
+    SnappyScatteredWriter<SnappySinkAllocator> writer(allocator);
+    return InternalUncompressAllTags(&decompressor, &writer, uncompressed_len);
+  }
+}

 } // end namespace snappy
-