Commit 1025d34a authored by vogelheim's avatar vogelheim Committed by Commit bot

Avoid excessive data copying for ExternalStreamingStream::SetBookmark.

BUG=v8:4422
R=jochen@chromium.org
LOG=Y

Review URL: https://codereview.chromium.org/1346613002

Cr-Commit-Position: refs/heads/master@{#30763}
parent 04087a7e
......@@ -347,6 +347,7 @@ size_t ExternalStreamingStream::FillBuffer(size_t position) {
current_data_length_ = source_stream_->GetMoreData(&current_data_);
current_data_offset_ = 0;
bool data_ends = current_data_length_ == 0;
bookmark_data_is_from_current_data_ = false;
// A caveat: a data chunk might end with bytes from an incomplete UTF-8
// character (the rest of the bytes will be in the next chunk).
......@@ -406,6 +407,15 @@ bool ExternalStreamingStream::SetBookmark() {
// - buffer_[buffer_cursor_ .. buffer_end_] => bookmark_buffer_
// - current_data_[.._offset_ .. .._length_] => bookmark_data_
// - utf8_split_char_buffer_* => bookmark_utf8_split...
//
// To make sure we don't unnecessarily copy data, we also maintain
// whether bookmark_data_ contains a copy of the current current_data_
// block. This is done with:
// - bookmark_data_is_from_current_data_
// - bookmark_data_offset_: offset into bookmark_data_
//
// Note that bookmark_data_is_from_current_data_ must be maintained
// whenever current_data_ is updated.
bookmark_ = pos_;
......@@ -415,10 +425,21 @@ bool ExternalStreamingStream::SetBookmark() {
CopyCharsUnsigned(bookmark_buffer_.start(), buffer_cursor_, buffer_length);
size_t data_length = current_data_length_ - current_data_offset_;
size_t bookmark_data_length = static_cast<size_t>(bookmark_data_.length());
if (bookmark_data_is_from_current_data_ &&
data_length < bookmark_data_length) {
// Fast case: bookmark_data_ was previously copied from the current
// data block, and we have enough data for this bookmark.
bookmark_data_offset_ = bookmark_data_length - data_length;
} else {
// Slow case: We need to copy current_data_.
bookmark_data_.Dispose();
bookmark_data_ = Vector<uint8_t>::New(static_cast<int>(data_length));
CopyBytes(bookmark_data_.start(), current_data_ + current_data_offset_,
data_length);
bookmark_data_is_from_current_data_ = true;
bookmark_data_offset_ = 0;
}
bookmark_utf8_split_char_buffer_length_ = utf8_split_char_buffer_length_;
for (size_t i = 0; i < utf8_split_char_buffer_length_; i++) {
......@@ -437,12 +458,14 @@ void ExternalStreamingStream::ResetToBookmark() {
// bookmark_data_* => current_data_*
// (current_data_ assumes ownership of its memory.)
uint8_t* data = new uint8_t[bookmark_data_.length()];
uint8_t* data = new uint8_t[bookmark_data_.length() - bookmark_data_offset_];
current_data_offset_ = 0;
current_data_length_ = bookmark_data_.length();
CopyCharsUnsigned(data, bookmark_data_.begin(), bookmark_data_.length());
current_data_length_ = bookmark_data_.length() - bookmark_data_offset_;
CopyCharsUnsigned(data, bookmark_data_.begin() + bookmark_data_offset_,
bookmark_data_.length());
delete[] current_data_;
current_data_ = data;
bookmark_data_is_from_current_data_ = true;
// bookmark_buffer_ needs to be copied to buffer_.
CopyCharsUnsigned(buffer_, bookmark_buffer_.begin(),
......@@ -463,6 +486,7 @@ void ExternalStreamingStream::FlushCurrent() {
current_data_ = NULL;
current_data_length_ = 0;
current_data_offset_ = 0;
bookmark_data_is_from_current_data_ = false;
}
......
......@@ -99,6 +99,8 @@ class ExternalStreamingStream : public BufferedUtf16CharacterStream {
current_data_length_(0),
utf8_split_char_buffer_length_(0),
bookmark_(0),
bookmark_data_is_from_current_data_(false),
bookmark_data_offset_(0),
bookmark_utf8_split_char_buffer_length_(0) {}
virtual ~ExternalStreamingStream() {
......@@ -139,6 +141,8 @@ class ExternalStreamingStream : public BufferedUtf16CharacterStream {
size_t bookmark_;
Vector<uint16_t> bookmark_buffer_;
Vector<uint8_t> bookmark_data_;
bool bookmark_data_is_from_current_data_;
size_t bookmark_data_offset_;
uint8_t bookmark_utf8_split_char_buffer_[4];
size_t bookmark_utf8_split_char_buffer_length_;
};
......
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