Componentize renderer side of DNS prefetching.

chrome/renderer/net/predictor_queue.h

-// Copyright (c) 2011 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.
-
-// DnsQueue is implemented as an almost FIFO circular buffer for text
-// strings that don't have embedded nulls ('\0').  The "almost" element is that
-// some duplicate strings may be removed (i.e., the string won't really be
-// pushed *if* the class happens to notice that a duplicate is already in the
-// queue).
-// The buffers internal format is null terminated character strings
-// (a.k.a., c_strings).
-// It is written to be as fast as possible during push() operations, so
-// that there will be minimal performance impact on a supplier thread.
-// The push() operation will not block, and no memory allocation is involved
-// (internally) during the push operations.
-// The one caveat is that if there is insufficient space in the buffer to
-// accept additional string via a push(), then the push() will fail, and
-// the buffer will be unmodified.
-
-// This class was designed for use in DNS prefetch operations.  During
-// rendering, the supplier is the renderer (typically), and the consumer
-// is a thread that sends messages to an async DNS resolver.
-
-#ifndef CHROME_RENDERER_NET_PREDICTOR_QUEUE_H__
-#define CHROME_RENDERER_NET_PREDICTOR_QUEUE_H__
-
-#include <string>
-
-#include "base/basictypes.h"
-#include "base/memory/scoped_ptr.h"
-
-class DnsQueue {
- public:
-  // BufferSize is a signed type used for indexing into a buffer.
-  typedef int32 BufferSize;
-
-  enum PushResult { SUCCESSFUL_PUSH, OVERFLOW_PUSH, REDUNDANT_PUSH };
-
-  // The size specified in the constructor creates a buffer large enough
-  // to hold at most one string of that length, or "many"
-  // strings of considerably shorter length.  Note that strings
-  // are padded internally with a terminal '\0" while stored,
-  // so if you are trying to be precise and get N strings of
-  // length K to fit, you should actually construct a buffer with
-  // an internal size of N*(K+1).
-  explicit DnsQueue(BufferSize size);
-  ~DnsQueue(void);
-
-  size_t Size() const { return size_; }
-  void Clear();
-
-  // Push takes an unterminated string of the given length
-  // and inserts it into the queue for later
-  // extraction by read.  For each successful push(), there
-  // can later be a corresponding read() to extracted the text.
-  // The string must not contain an embedded null terminator
-  // Exactly length chars are written, or the push fails (where
-  // "fails" means nothing is written).
-  // Returns true for success, false for failure (nothing written).
-  PushResult Push(const char* source, const size_t length);
-
-  PushResult Push(std::string source) {
-    return Push(source.c_str(), source.length());
-  }
-
-  // Extract the next available string from the buffer.
-  // If the buffer is empty, then return false.
-  bool Pop(std::string* out_string);
-
- private:
-  bool Validate();  // Checks that all internal data is valid.
-
-  const scoped_ptr<char[]> buffer_;  // Circular buffer, plus extra char ('\0').
-  const BufferSize buffer_size_;  // Size one smaller than allocated space.
-  const BufferSize buffer_sentinel_;  // Index of extra '\0' at end of buffer_.
-
-  // If writable_ == readable_, then the buffer is empty.
-  BufferSize readable_;  // Next readable char in buffer_.
-  BufferSize writeable_;  // The next space in buffer_ to push.
-
-  // Number of queued strings
-  size_t size_;
-
-  DISALLOW_COPY_AND_ASSIGN(DnsQueue);
-};  // class DnsQueue
-
-#endif  // CHROME_RENDERER_NET_PREDICTOR_QUEUE_H__