tor-browser

The Tor Browser
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StartupCache.h (11258B)

      1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
      2 /* This Source Code Form is subject to the terms of the Mozilla Public
      3 * License, v. 2.0. If a copy of the MPL was not distributed with this
      4 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
      5 
      6 #ifndef StartupCache_h_
      7 #define StartupCache_h_
      8 
      9 #include <utility>
     10 
     11 #include "nsClassHashtable.h"
     12 #include "nsComponentManagerUtils.h"
     13 #include "nsTArray.h"
     14 #include "nsTHashSet.h"
     15 #include "nsTStringHasher.h"  // mozilla::DefaultHasher<nsCString>
     16 #include "nsZipArchive.h"
     17 #include "nsITimer.h"
     18 #include "nsIMemoryReporter.h"
     19 #include "nsIObserverService.h"
     20 #include "nsIObserver.h"
     21 #include "nsIObjectOutputStream.h"
     22 #include "nsIFile.h"
     23 #include "mozilla/Attributes.h"
     24 #include "mozilla/AutoMemMap.h"
     25 #include "mozilla/Compression.h"
     26 #include "mozilla/MemoryReporting.h"
     27 #include "mozilla/Monitor.h"
     28 #include "mozilla/Mutex.h"
     29 #include "mozilla/Result.h"
     30 #include "mozilla/UniquePtr.h"
     31 #include "mozilla/UniquePtrExtensions.h"
     32 
     33 /**
     34 * The StartupCache is a persistent cache of simple key-value pairs,
     35 * where the keys are null-terminated c-strings and the values are
     36 * arbitrary data, passed as a (char*, size) tuple.
     37 *
     38 * Clients should use the GetSingleton() static method to access the cache. It
     39 * will be available from the end of XPCOM init (NS_InitXPCOM3 in
     40 * XPCOMInit.cpp), until XPCOM shutdown begins. The GetSingleton() method will
     41 * return null if the cache is unavailable. The cache is only provided for
     42 * libxul builds -- it will fail to link in non-libxul builds. The XPCOM
     43 * interface is provided only to allow compiled-code tests; clients should avoid
     44 * using it.
     45 *
     46 * The API provided is very simple: GetBuffer() returns a buffer that was
     47 * previously stored in the cache (if any), and PutBuffer() inserts a buffer
     48 * into the cache. GetBuffer returns a new buffer, and the caller must take
     49 * ownership of it. PutBuffer will assert if the client attempts to insert a
     50 * buffer with the same name as an existing entry. The cache makes a copy of the
     51 * passed-in buffer, so client retains ownership.
     52 *
     53 * InvalidateCache() may be called if a client suspects data corruption
     54 * or wishes to invalidate for any other reason. This will remove all existing
     55 * cache data. Additionally, the static method IgnoreDiskCache() can be called
     56 * if it is believed that the on-disk cache file is itself corrupt. This call
     57 * implicitly calls InvalidateCache (if the singleton has been initialized) to
     58 * ensure any data already read from disk is discarded. The cache will not load
     59 * data from the disk file until a successful write occurs.
     60 *
     61 * Finally, getDebugObjectOutputStream() allows debug code to wrap an
     62 * objectstream with a debug objectstream, to check for multiply-referenced
     63 * objects. These will generally fail to deserialize correctly, unless they are
     64 * stateless singletons or the client maintains their own object data map for
     65 * deserialization.
     66 *
     67 * Writes before the final-ui-startup notification are placed in an intermediate
     68 * cache in memory, then written out to disk at a later time, to get writes off
     69 * the startup path. In any case, clients should not rely on being able to
     70 * GetBuffer() data that is written to the cache, since it may not have been
     71 * written to disk or another client may have invalidated the cache. In other
     72 * words, it should be used as a cache only, and not a reliable persistent
     73 * store.
     74 *
     75 * Some utility functions are provided in StartupCacheUtils. These functions
     76 * wrap the buffers into object streams, which may be useful for serializing
     77 * objects. Note the above caution about multiply-referenced objects, though --
     78 * the streams are just as 'dumb' as the underlying buffers about
     79 * multiply-referenced objects. They just provide some convenience in writing
     80 * out data.
     81 */
     82 
     83 namespace mozilla {
     84 
     85 namespace scache {
     86 
     87 struct StartupCacheEntry {
     88  UniqueFreePtr<char[]> mData;
     89  uint32_t mOffset;
     90  uint32_t mCompressedSize;
     91  uint32_t mUncompressedSize;
     92  int32_t mHeaderOffsetInFile;
     93  int32_t mRequestedOrder;
     94  bool mRequested;
     95 
     96  MOZ_IMPLICIT StartupCacheEntry(uint32_t aOffset, uint32_t aCompressedSize,
     97                                 uint32_t aUncompressedSize)
     98      : mData(nullptr),
     99        mOffset(aOffset),
    100        mCompressedSize(aCompressedSize),
    101        mUncompressedSize(aUncompressedSize),
    102        mHeaderOffsetInFile(0),
    103        mRequestedOrder(0),
    104        mRequested(false) {}
    105 
    106  StartupCacheEntry(UniqueFreePtr<char[]> aData, size_t aLength,
    107                    int32_t aRequestedOrder)
    108      : mData(std::move(aData)),
    109        mOffset(0),
    110        mCompressedSize(0),
    111        mUncompressedSize(aLength),
    112        mHeaderOffsetInFile(0),
    113        mRequestedOrder(0),
    114        mRequested(true) {}
    115 
    116  // std::pair is not trivially move assignable/constructible, so make our own.
    117  struct KeyValuePair {
    118    const nsCString* first;
    119    StartupCacheEntry* second;
    120    KeyValuePair(const nsCString* aKeyPtr, StartupCacheEntry* aValuePtr)
    121        : first(aKeyPtr), second(aValuePtr) {}
    122  };
    123  static_assert(std::is_trivially_move_assignable<KeyValuePair>::value);
    124  static_assert(std::is_trivially_move_constructible<KeyValuePair>::value);
    125 
    126  struct Comparator {
    127    using Value = KeyValuePair;
    128 
    129    bool Equals(const Value& a, const Value& b) const {
    130      return a.second->mRequestedOrder == b.second->mRequestedOrder;
    131    }
    132 
    133    bool LessThan(const Value& a, const Value& b) const {
    134      return a.second->mRequestedOrder < b.second->mRequestedOrder;
    135    }
    136  };
    137 };
    138 
    139 // We don't want to refcount StartupCache, and ObserverService wants to
    140 // refcount its listeners, so we'll let it refcount this instead.
    141 class StartupCacheListener final : public nsIObserver {
    142  ~StartupCacheListener() = default;
    143  NS_DECL_THREADSAFE_ISUPPORTS
    144  NS_DECL_NSIOBSERVER
    145 };
    146 
    147 class StartupCache : public nsIMemoryReporter {
    148  friend class StartupCacheListener;
    149 
    150 public:
    151  NS_DECL_THREADSAFE_ISUPPORTS
    152  NS_DECL_NSIMEMORYREPORTER
    153 
    154  // StartupCache methods. See above comments for a more detailed description.
    155 
    156  // true if the archive has an entry for the buffer or not.
    157  bool HasEntry(const char* id);
    158 
    159  // Returns a buffer that was previously stored, caller does not take ownership
    160  nsresult GetBuffer(const char* id, const char** outbuf, uint32_t* length);
    161 
    162  // Stores a buffer. Caller yields ownership.
    163  nsresult PutBuffer(const char* id, UniqueFreePtr<char[]>&& inbuf,
    164                     uint32_t length);
    165 
    166  // Removes the cache file.
    167  void InvalidateCache(bool memoryOnly = false);
    168 
    169  // If some event knowingly re-generates the startup cache (like live language
    170  // switching) count these events in order to allow them.
    171  void CountAllowedInvalidation();
    172 
    173  // For use during shutdown - this will write the startupcache's data
    174  // to disk if the timer hasn't already gone off.
    175  void MaybeInitShutdownWrite();
    176 
    177  // For use during shutdown - ensure we complete the shutdown write
    178  // before shutdown, even in the FastShutdown case.
    179  void EnsureShutdownWriteComplete();
    180 
    181  // Signal that data should not be loaded from the cache file
    182  static void IgnoreDiskCache();
    183 
    184  static bool GetIgnoreDiskCache();
    185 
    186  // In DEBUG builds, returns a stream that will attempt to check for
    187  // and disallow multiple writes of the same object.
    188  nsresult GetDebugObjectOutputStream(nsIObjectOutputStream* aStream,
    189                                      nsIObjectOutputStream** outStream);
    190 
    191  static StartupCache* GetSingletonNoInit();
    192  static StartupCache* GetSingleton();
    193  static void DeleteSingleton();
    194 
    195  // This measures all the heap memory used by the StartupCache, i.e. it
    196  // excludes the mapping.
    197  size_t HeapSizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const
    198      MOZ_REQUIRES(mTableLock);
    199 
    200  bool ShouldCompactCache() MOZ_REQUIRES(mTableLock);
    201  nsresult ResetStartupWriteTimerCheckingReadCount();
    202  nsresult ResetStartupWriteTimerAndLock();
    203  nsresult ResetStartupWriteTimer() MOZ_REQUIRES(mTableLock);
    204  bool StartupWriteComplete();
    205 
    206 private:
    207  StartupCache();
    208  virtual ~StartupCache();
    209 
    210  friend class StartupCacheInfo;
    211 
    212  Result<Ok, nsresult> LoadArchive() MOZ_REQUIRES(mTableLock);
    213  nsresult Init();
    214 
    215  // Returns a file pointer for the cache file with the given name in the
    216  // current profile.
    217  Result<nsCOMPtr<nsIFile>, nsresult> GetCacheFile(const nsAString& suffix);
    218 
    219  // Opens the cache file for reading.
    220  Result<Ok, nsresult> OpenCache();
    221 
    222  // Writes the cache to disk
    223  Result<Ok, nsresult> WriteToDisk() MOZ_REQUIRES(mTableLock);
    224 
    225  void WaitOnPrefetch();
    226  void StartPrefetchMemory() MOZ_REQUIRES(mTableLock);
    227 
    228  static nsresult InitSingleton();
    229  static void WriteTimeout(nsITimer* aTimer, void* aClosure);
    230  void MaybeWriteOffMainThread();
    231  void ThreadedPrefetch(uint8_t* aStart, size_t aSize);
    232 
    233  Monitor mPrefetchComplete{"StartupCachePrefetch"};
    234  bool mPrefetchInProgress MOZ_GUARDED_BY(mPrefetchComplete){false};
    235 
    236  // This is normally accessed on MainThread, but WriteToDisk() can
    237  // access it on other threads
    238  HashMap<nsCString, StartupCacheEntry> mTable MOZ_GUARDED_BY(mTableLock);
    239  // This owns references to the contents of tables which have been invalidated.
    240  // In theory it grows forever if the cache is continually filled and then
    241  // invalidated, but this should not happen in practice. Deleting old tables
    242  // could create dangling pointers. RefPtrs could be introduced, but it would
    243  // be a large amount of error-prone work to change.
    244  nsTArray<decltype(mTable)> mOldTables MOZ_GUARDED_BY(mTableLock);
    245  size_t mAllowedInvalidationsCount;
    246  nsCOMPtr<nsIFile> mFile;
    247  mozilla::loader::AutoMemMap mCacheData MOZ_GUARDED_BY(mTableLock);
    248  Mutex mTableLock;
    249 
    250  nsCOMPtr<nsIObserverService> mObserverService;
    251  RefPtr<StartupCacheListener> mListener;
    252  nsCOMPtr<nsITimer> mTimer;
    253 
    254  bool mDirty MOZ_GUARDED_BY(mTableLock);
    255  bool mWrittenOnce MOZ_GUARDED_BY(mTableLock);
    256  bool mCurTableReferenced MOZ_GUARDED_BY(mTableLock);
    257 
    258  uint32_t mRequestedCount;
    259  size_t mCacheEntriesBaseOffset;
    260 
    261  static StaticRefPtr<StartupCache> gStartupCache;
    262  static bool gShutdownInitiated;
    263  static bool gIgnoreDiskCache;
    264  static bool gFoundDiskCacheOnInit;
    265 
    266  UniquePtr<Compression::LZ4FrameDecompressionContext> mDecompressionContext;
    267 #ifdef DEBUG
    268  nsTHashSet<nsCOMPtr<nsISupports>> mWriteObjectMap;
    269 #endif
    270 };
    271 
    272 // This debug outputstream attempts to detect if clients are writing multiple
    273 // references to the same object. We only support that if that object
    274 // is a singleton.
    275 #ifdef DEBUG
    276 class StartupCacheDebugOutputStream final : public nsIObjectOutputStream {
    277  ~StartupCacheDebugOutputStream() = default;
    278 
    279  NS_DECL_ISUPPORTS
    280  NS_DECL_NSIOBJECTOUTPUTSTREAM
    281 
    282  StartupCacheDebugOutputStream(nsIObjectOutputStream* binaryStream,
    283                                nsTHashSet<nsCOMPtr<nsISupports>>* objectMap)
    284      : mBinaryStream(binaryStream), mObjectMap(objectMap) {}
    285 
    286  NS_FORWARD_SAFE_NSIBINARYOUTPUTSTREAM(mBinaryStream)
    287  NS_FORWARD_SAFE_NSIOUTPUTSTREAM(mBinaryStream)
    288 
    289  bool CheckReferences(nsISupports* aObject);
    290 
    291  nsCOMPtr<nsIObjectOutputStream> mBinaryStream;
    292  nsTHashSet<nsCOMPtr<nsISupports>>* mObjectMap;
    293 };
    294 #endif  // DEBUG
    295 
    296 }  // namespace scache
    297 }  // namespace mozilla
    298 
    299 #endif  // StartupCache_h_