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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "chrome/browser/media_galleries/fileapi/readahead_file_stream_reader.h"
#include <stddef.h>
#include <algorithm>
#include "base/message_loop/message_loop.h"
#include "base/numerics/safe_conversions.h"
#include "net/base/io_buffer.h"
#include "net/base/net_errors.h"
using storage::FileStreamReader;
namespace {
const size_t kDesiredNumberOfBuffers = 2; // So we are always one buffer ahead.
const int kBufferSize = 1024*1024; // 1MB to minimize transaction costs.
} // namespace
ReadaheadFileStreamReader::ReadaheadFileStreamReader(FileStreamReader* source)
: source_(source),
source_error_(0),
source_has_pending_read_(false),
weak_factory_(this) {
}
ReadaheadFileStreamReader::~ReadaheadFileStreamReader() {}
int ReadaheadFileStreamReader::Read(
net::IOBuffer* buf, int buf_len, const net::CompletionCallback& callback) {
DCHECK(!pending_sink_buffer_.get());
DCHECK(pending_read_callback_.is_null());
ReadFromSourceIfNeeded();
scoped_refptr<net::DrainableIOBuffer> sink =
new net::DrainableIOBuffer(buf, buf_len);
int result = FinishReadFromCacheOrStoredError(sink.get());
// We are waiting for an source read to complete, so save the request.
if (result == net::ERR_IO_PENDING) {
DCHECK(!pending_sink_buffer_.get());
DCHECK(pending_read_callback_.is_null());
pending_sink_buffer_ = sink;
pending_read_callback_ = callback;
}
return result;
}
int64_t ReadaheadFileStreamReader::GetLength(
const net::Int64CompletionCallback& callback) {
return source_->GetLength(callback);
}
int ReadaheadFileStreamReader::FinishReadFromCacheOrStoredError(
net::DrainableIOBuffer* sink) {
// If we don't have any ready cache, return the pending read code, or
// the stored error code.
if (buffers_.empty()) {
if (source_.get()) {
DCHECK(source_has_pending_read_);
return net::ERR_IO_PENDING;
} else {
return source_error_;
}
}
while (sink->BytesRemaining() > 0 && !buffers_.empty()) {
net::DrainableIOBuffer* source_buffer = buffers_.front().get();
DCHECK(source_buffer->BytesRemaining() > 0);
int copy_len = std::min(source_buffer->BytesRemaining(),
sink->BytesRemaining());
std::copy(source_buffer->data(), source_buffer->data() + copy_len,
sink->data());
source_buffer->DidConsume(copy_len);
sink->DidConsume(copy_len);
if (source_buffer->BytesRemaining() == 0) {
buffers_.pop();
// Get a new buffer to replace the one we just used up.
ReadFromSourceIfNeeded();
}
}
return sink->BytesConsumed();
}
void ReadaheadFileStreamReader::ReadFromSourceIfNeeded() {
if (!source_.get() || source_has_pending_read_ ||
buffers_.size() >= kDesiredNumberOfBuffers) {
return;
}
source_has_pending_read_ = true;
scoped_refptr<net::IOBuffer> buf(new net::IOBuffer(kBufferSize));
int result = source_->Read(
buf.get(), kBufferSize,
base::Bind(&ReadaheadFileStreamReader::OnFinishReadFromSource,
weak_factory_.GetWeakPtr(), base::RetainedRef(buf)));
if (result != net::ERR_IO_PENDING)
OnFinishReadFromSource(buf.get(), result);
}
void ReadaheadFileStreamReader::OnFinishReadFromSource(net::IOBuffer* buf,
int result) {
DCHECK(result != net::ERR_IO_PENDING);
DCHECK(source_has_pending_read_);
source_has_pending_read_ = false;
// Either store the data read from |source_|, or store the error code.
if (result > 0) {
scoped_refptr<net::DrainableIOBuffer> drainable_buffer(
new net::DrainableIOBuffer(buf, result));
buffers_.push(drainable_buffer);
ReadFromSourceIfNeeded();
} else {
source_.reset();
source_error_ = result;
}
// If there's a read request waiting for the source FileStreamReader to
// finish reading, fulfill that request now from the cache or stored error.
if (pending_sink_buffer_.get()) {
DCHECK(!pending_read_callback_.is_null());
// Free the pending callback before running it, as the callback often
// dispatches another read.
scoped_refptr<net::DrainableIOBuffer> sink = pending_sink_buffer_;
pending_sink_buffer_ = NULL;
net::CompletionCallback completion_callback = pending_read_callback_;
pending_read_callback_.Reset();
completion_callback.Run(FinishReadFromCacheOrStoredError(sink.get()));
}
}
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