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