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 <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   struct Comparator {
 117     using Value = std::pair<const nsCString*, StartupCacheEntry*>;
 118
 119     bool Equals(const Value& a, const Value& b) const {
 120       return a.second->mRequestedOrder == b.second->mRequestedOrder;
 121     }
 122
 123     bool LessThan(const Value& a, const Value& b) const {
 124       return a.second->mRequestedOrder < b.second->mRequestedOrder;
 125     }
 126   };
 127 };
 128
 129 // We don't want to refcount StartupCache, and ObserverService wants to
 130 // refcount its listeners, so we'll let it refcount this instead.
 131 class StartupCacheListener final : public nsIObserver {
 132   ~StartupCacheListener() = default;
 133   NS_DECL_THREADSAFE_ISUPPORTS
 134   NS_DECL_NSIOBSERVER
 135 };
 136
 137 class StartupCache : public nsIMemoryReporter {
 138   friend class StartupCacheListener;
 139
 140  public:
 141   NS_DECL_THREADSAFE_ISUPPORTS
 142   NS_DECL_NSIMEMORYREPORTER
 143
 144   // StartupCache methods. See above comments for a more detailed description.
 145
 146   // true if the archive has an entry for the buffer or not.
 147   bool HasEntry(const char* id);
 148
 149   // Returns a buffer that was previously stored, caller does not take ownership
 150   nsresult GetBuffer(const char* id, const char** outbuf, uint32_t* length);
 151
 152   // Stores a buffer. Caller yields ownership.
 153   nsresult PutBuffer(const char* id, UniqueFreePtr<char[]>&& inbuf,
 154                      uint32_t length);
 155
 156   // Removes the cache file.
 157   void InvalidateCache(bool memoryOnly = false);
 158
 159   // If some event knowingly re-generates the startup cache (like live language
 160   // switching) count these events in order to allow them.
 161   void CountAllowedInvalidation();
 162
 163   // For use during shutdown - this will write the startupcache's data
 164   // to disk if the timer hasn't already gone off.
 165   void MaybeInitShutdownWrite();
 166
 167   // For use during shutdown - ensure we complete the shutdown write
 168   // before shutdown, even in the FastShutdown case.
 169   void EnsureShutdownWriteComplete();
 170
 171   // Signal that data should not be loaded from the cache file
 172   static void IgnoreDiskCache();
 173
 174   static bool GetIgnoreDiskCache();
 175
 176   // In DEBUG builds, returns a stream that will attempt to check for
 177   // and disallow multiple writes of the same object.
 178   nsresult GetDebugObjectOutputStream(nsIObjectOutputStream* aStream,
 179                                       nsIObjectOutputStream** outStream);
 180
 181   static StartupCache* GetSingletonNoInit();
 182   static StartupCache* GetSingleton();
 183   static void DeleteSingleton();
 184
 185   // This measures all the heap memory used by the StartupCache, i.e. it
 186   // excludes the mapping.
 187   size_t HeapSizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const
 188       MOZ_REQUIRES(mTableLock);
 189
 190   bool ShouldCompactCache() MOZ_REQUIRES(mTableLock);
 191   nsresult ResetStartupWriteTimerCheckingReadCount();
 192   nsresult ResetStartupWriteTimerAndLock();
 193   nsresult ResetStartupWriteTimer() MOZ_REQUIRES(mTableLock);
 194   bool StartupWriteComplete();
 195
 196  private:
 197   StartupCache();
 198   virtual ~StartupCache();
 199
 200   friend class StartupCacheInfo;
 201
 202   Result<Ok, nsresult> LoadArchive();
 203   nsresult Init();
 204
 205   // Returns a file pointer for the cache file with the given name in the
 206   // current profile.
 207   Result<nsCOMPtr<nsIFile>, nsresult> GetCacheFile(const nsAString& suffix);
 208
 209   // Opens the cache file for reading.
 210   Result<Ok, nsresult> OpenCache();
 211
 212   // Writes the cache to disk
 213   Result<Ok, nsresult> WriteToDisk() MOZ_REQUIRES(mTableLock);
 214
 215   void WaitOnPrefetch();
 216   void StartPrefetchMemory();
 217
 218   static nsresult InitSingleton();
 219   static void WriteTimeout(nsITimer* aTimer, void* aClosure);
 220   void MaybeWriteOffMainThread();
 221   void ThreadedPrefetch();
 222
 223   Monitor mPrefetchComplete{"StartupCachePrefetch"};
 224   bool mPrefetchInProgress MOZ_GUARDED_BY(mPrefetchComplete){false};
 225
 226   // This is normally accessed on MainThread, but WriteToDisk() can
 227   // access it on other threads
 228   HashMap<nsCString, StartupCacheEntry> mTable MOZ_GUARDED_BY(mTableLock);
 229   // This owns references to the contents of tables which have been invalidated.
 230   // In theory it grows forever if the cache is continually filled and then
 231   // invalidated, but this should not happen in practice. Deleting old tables
 232   // could create dangling pointers. RefPtrs could be introduced, but it would
 233   // be a large amount of error-prone work to change.
 234   nsTArray<decltype(mTable)> mOldTables MOZ_GUARDED_BY(mTableLock);
 235   size_t mAllowedInvalidationsCount;
 236   nsCOMPtr<nsIFile> mFile;
 237   loader::AutoMemMap mCacheData MOZ_GUARDED_BY(mTableLock);
 238   Mutex mTableLock;
 239
 240   nsCOMPtr<nsIObserverService> mObserverService;
 241   RefPtr<StartupCacheListener> mListener;
 242   nsCOMPtr<nsITimer> mTimer;
 243
 244   bool mDirty MOZ_GUARDED_BY(mTableLock);
 245   bool mWrittenOnce MOZ_GUARDED_BY(mTableLock);
 246   bool mCurTableReferenced MOZ_GUARDED_BY(mTableLock);
 247
 248   uint32_t mRequestedCount;
 249   size_t mCacheEntriesBaseOffset;
 250
 251   static StaticRefPtr<StartupCache> gStartupCache;
 252   static bool gShutdownInitiated;
 253   static bool gIgnoreDiskCache;
 254   static bool gFoundDiskCacheOnInit;
 255
 256   UniquePtr<Compression::LZ4FrameDecompressionContext> mDecompressionContext;
 257 #ifdef DEBUG
 258   nsTHashSet<nsCOMPtr<nsISupports>> mWriteObjectMap;
 259 #endif
 260 };
 261
 262 // This debug outputstream attempts to detect if clients are writing multiple
 263 // references to the same object. We only support that if that object
 264 // is a singleton.
 265 #ifdef DEBUG
 266 class StartupCacheDebugOutputStream final : public nsIObjectOutputStream {
 267   ~StartupCacheDebugOutputStream() = default;
 268
 269   NS_DECL_ISUPPORTS
 270   NS_DECL_NSIOBJECTOUTPUTSTREAM
 271
 272   StartupCacheDebugOutputStream(nsIObjectOutputStream* binaryStream,
 273                                 nsTHashSet<nsCOMPtr<nsISupports>>* objectMap)
 274       : mBinaryStream(binaryStream), mObjectMap(objectMap) {}
 275
 276   NS_FORWARD_SAFE_NSIBINARYOUTPUTSTREAM(mBinaryStream)
 277   NS_FORWARD_SAFE_NSIOUTPUTSTREAM(mBinaryStream)
 278
 279   bool CheckReferences(nsISupports* aObject);
 280
 281   nsCOMPtr<nsIObjectOutputStream> mBinaryStream;
 282   nsTHashSet<nsCOMPtr<nsISupports>>* mObjectMap;
 283 };
 284 #endif  // DEBUG
 285
 286 }  // namespace scache
 287 }  // namespace mozilla
 288
 289 #endif  // StartupCache_h_