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