startupcache/StartupCache.h

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