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