gecko-dev/startupcache/StartupCache.h

/* -*-  Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef StartupCache_h_
#define StartupCache_h_

#include "nsClassHashtable.h"
#include "nsComponentManagerUtils.h"
#include "nsTArray.h"
#include "nsZipArchive.h"
#include "nsITimer.h"
#include "nsIMemoryReporter.h"
#include "nsIObserverService.h"
#include "nsIObserver.h"
#include "nsIObjectOutputStream.h"
#include "nsIOutputStream.h"
#include "nsIFile.h"
#include "mozilla/Attributes.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/UniquePtr.h"

/**
 * The StartupCache is a persistent cache of simple key-value pairs,
 * where the keys are null-terminated c-strings and the values are
 * arbitrary data, passed as a (char*, size) tuple.
 *
 * Clients should use the GetSingleton() static method to access the cache. It
 * will be available from the end of XPCOM init (NS_InitXPCOM3 in XPCOMInit.cpp),
 * until XPCOM shutdown begins. The GetSingleton() method will return null if the cache
 * is unavailable. The cache is only provided for libxul builds --
 * it will fail to link in non-libxul builds. The XPCOM interface is provided
 * only to allow compiled-code tests; clients should avoid using it.
 *
 * The API provided is very simple: GetBuffer() returns a buffer that was previously
 * stored in the cache (if any), and PutBuffer() inserts a buffer into the cache.
 * GetBuffer returns a new buffer, and the caller must take ownership of it.
 * PutBuffer will assert if the client attempts to insert a buffer with the same name as
 * an existing entry. The cache makes a copy of the passed-in buffer, so client
 * retains ownership.
 *
 * InvalidateCache() may be called if a client suspects data corruption
 * or wishes to invalidate for any other reason. This will remove all existing cache data.
 * Additionally, the static method IgnoreDiskCache() can be called if it is
 * believed that the on-disk cache file is itself corrupt. This call implicitly
 * calls InvalidateCache (if the singleton has been initialized) to ensure any
 * data already read from disk is discarded. The cache will not load data from
 * the disk file until a successful write occurs.
 *
 * Finally, getDebugObjectOutputStream() allows debug code to wrap an objectstream
 * with a debug objectstream, to check for multiply-referenced objects. These will
 * generally fail to deserialize correctly, unless they are stateless singletons or the
 * client maintains their own object data map for deserialization.
 *
 * Writes before the final-ui-startup notification are placed in an intermediate
 * cache in memory, then written out to disk at a later time, to get writes off the
 * startup path. In any case, clients should not rely on being able to GetBuffer()
 * data that is written to the cache, since it may not have been written to disk or
 * another client may have invalidated the cache. In other words, it should be used as
 * a cache only, and not a reliable persistent store.
 *
 * Some utility functions are provided in StartupCacheUtils. These functions wrap the
 * buffers into object streams, which may be useful for serializing objects. Note
 * the above caution about multiply-referenced objects, though -- the streams are just
 * as 'dumb' as the underlying buffers about multiply-referenced objects. They just
 * provide some convenience in writing out data.
 */

namespace mozilla {

namespace scache {

struct CacheEntry
{
  UniquePtr<char[]> data;
  uint32_t size;

  CacheEntry() : size(0) { }

  // Takes possession of buf
  CacheEntry(UniquePtr<char[]> buf, uint32_t len) : data(Move(buf)), size(len) { }

  ~CacheEntry()
  {
  }

  size_t SizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) {
    return mallocSizeOf(this) + mallocSizeOf(data.get());
  }
};

// We don't want to refcount StartupCache, and ObserverService wants to
// refcount its listeners, so we'll let it refcount this instead.
class StartupCacheListener final : public nsIObserver
{
  ~StartupCacheListener() {}
  NS_DECL_THREADSAFE_ISUPPORTS
  NS_DECL_NSIOBSERVER
};

class StartupCache : public nsIMemoryReporter
{

friend class StartupCacheListener;

public:
  NS_DECL_THREADSAFE_ISUPPORTS
  NS_DECL_NSIMEMORYREPORTER

  // StartupCache methods. See above comments for a more detailed description.

  // Returns a buffer that was previously stored, caller takes ownership.
  nsresult GetBuffer(const char* id, UniquePtr<char[]>* outbuf, uint32_t* length);

  // Stores a buffer. Caller yields ownership.
  nsresult PutBuffer(const char* id, UniquePtr<char[]>&& inbuf, uint32_t length);

  // Removes the cache file.
  void InvalidateCache();

  // Signal that data should not be loaded from the cache file
  static void IgnoreDiskCache();

  // In DEBUG builds, returns a stream that will attempt to check for
  // and disallow multiple writes of the same object.
  nsresult GetDebugObjectOutputStream(nsIObjectOutputStream* aStream,
                                      nsIObjectOutputStream** outStream);

  static StartupCache* GetSingleton();
  static void DeleteSingleton();

  // This measures all the heap memory used by the StartupCache, i.e. it
  // excludes the mapping.
  size_t HeapSizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const;

  size_t SizeOfMapping();

  // FOR TESTING ONLY
  nsresult ResetStartupWriteTimer();
  bool StartupWriteComplete();
private:
  StartupCache();
  virtual ~StartupCache();

  nsresult LoadArchive();
  nsresult Init();
  void WriteToDisk();
  void WaitOnWriteThread();

  static nsresult InitSingleton();
  static void WriteTimeout(nsITimer *aTimer, void *aClosure);
  static void ThreadedWrite(void *aClosure);

  nsClassHashtable<nsCStringHashKey, CacheEntry> mTable;
  nsTArray<nsCString> mPendingWrites;
  RefPtr<nsZipArchive> mArchive;
  nsCOMPtr<nsIFile> mFile;

  nsCOMPtr<nsIObserverService> mObserverService;
  RefPtr<StartupCacheListener> mListener;
  nsCOMPtr<nsITimer> mTimer;

  bool mStartupWriteInitiated;

  static StaticRefPtr<StartupCache> gStartupCache;
  static bool gShutdownInitiated;
  static bool gIgnoreDiskCache;
  PRThread *mWriteThread;
#ifdef DEBUG
  nsTHashtable<nsISupportsHashKey> mWriteObjectMap;
#endif
};

// This debug outputstream attempts to detect if clients are writing multiple
// references to the same object. We only support that if that object
// is a singleton.
#ifdef DEBUG
class StartupCacheDebugOutputStream final
  : public nsIObjectOutputStream
{
  ~StartupCacheDebugOutputStream() {}

  NS_DECL_ISUPPORTS
  NS_DECL_NSIOBJECTOUTPUTSTREAM

  StartupCacheDebugOutputStream (nsIObjectOutputStream* binaryStream,
                                   nsTHashtable<nsISupportsHashKey>* objectMap)
  : mBinaryStream(binaryStream), mObjectMap(objectMap) { }

  NS_FORWARD_SAFE_NSIBINARYOUTPUTSTREAM(mBinaryStream)
  NS_FORWARD_SAFE_NSIOUTPUTSTREAM(mBinaryStream)

  bool CheckReferences(nsISupports* aObject);

  nsCOMPtr<nsIObjectOutputStream> mBinaryStream;
  nsTHashtable<nsISupportsHashKey> *mObjectMap;
};
#endif // DEBUG

} // namespace scache
} // namespace mozilla

#endif //StartupCache_h_