/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ /* This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/** * The StartupCache is a persistent cache of simple key-value pairs, * where the keys are null-terminated c-strings and the values are * arbitrary data, passed as a (char*, size) tuple. * * Clients should use the GetSingleton() static method to access the cache. It * will be available from the end of XPCOM init (NS_InitXPCOM3 in * XPCOMInit.cpp), until XPCOM shutdown begins. The GetSingleton() method will * return null if the cache is unavailable. The cache is only provided for * libxul builds -- it will fail to link in non-libxul builds. The XPCOM * interface is provided only to allow compiled-code tests; clients should avoid * using it. * * The API provided is very simple: GetBuffer() returns a buffer that was * previously stored in the cache (if any), and PutBuffer() inserts a buffer * into the cache. GetBuffer returns a new buffer, and the caller must take * ownership of it. PutBuffer will assert if the client attempts to insert a * buffer with the same name as an existing entry. The cache makes a copy of the * passed-in buffer, so client retains ownership. * * InvalidateCache() may be called if a client suspects data corruption * or wishes to invalidate for any other reason. This will remove all existing * cache data. Additionally, the static method IgnoreDiskCache() can be called * if it is believed that the on-disk cache file is itself corrupt. This call * implicitly calls InvalidateCache (if the singleton has been initialized) to * ensure any data already read from disk is discarded. The cache will not load * data from the disk file until a successful write occurs. * * Finally, getDebugObjectOutputStream() allows debug code to wrap an * objectstream with a debug objectstream, to check for multiply-referenced * objects. These will generally fail to deserialize correctly, unless they are * stateless singletons or the client maintains their own object data map for * deserialization. * * Writes before the final-ui-startup notification are placed in an intermediate * cache in memory, then written out to disk at a later time, to get writes off * the startup path. In any case, clients should not rely on being able to * GetBuffer() data that is written to the cache, since it may not have been * written to disk or another client may have invalidated the cache. In other * words, it should be used as a cache only, and not a reliable persistent * store. * * Some utility functions are provided in StartupCacheUtils. These functions * wrap the buffers into object streams, which may be useful for serializing * objects. Note the above caution about multiply-referenced objects, though -- * the streams are just as 'dumb' as the underlying buffers about * multiply-referenced objects. They just provide some convenience in writing * out data.
*/
// std::pair is not trivially move assignable/constructible, so make our own. struct KeyValuePair { const nsCString* first;
StartupCacheEntry* second;
KeyValuePair(const nsCString* aKeyPtr, StartupCacheEntry* aValuePtr)
: first(aKeyPtr), second(aValuePtr) {}
};
static_assert(std::is_trivially_move_assignable<KeyValuePair>::value);
static_assert(std::is_trivially_move_constructible<KeyValuePair>::value);
struct Comparator { using Value = KeyValuePair;
bool Equals(const Value& a, const Value& b) const { return a.second->mRequestedOrder == b.second->mRequestedOrder;
}
bool LessThan(const Value& a, const Value& b) const { return a.second->mRequestedOrder < b.second->mRequestedOrder;
}
};
};
// We don't want to refcount StartupCache, and ObserverService wants to // refcount its listeners, so we'll let it refcount this instead. class StartupCacheListener final : public nsIObserver {
~StartupCacheListener() = default;
NS_DECL_THREADSAFE_ISUPPORTS
NS_DECL_NSIOBSERVER
};
class StartupCache : public nsIMemoryReporter { friendclass StartupCacheListener;
// StartupCache methods. See above comments for a more detailed description.
// true if the archive has an entry for the buffer or not. bool HasEntry(constchar* id);
// Returns a buffer that was previously stored, caller does not take ownership
nsresult GetBuffer(constchar* id, constchar** outbuf, uint32_t* length);
// Removes the cache file. void InvalidateCache(bool memoryOnly = false);
// If some event knowingly re-generates the startup cache (like live language // switching) count these events in order to allow them. void CountAllowedInvalidation();
// For use during shutdown - this will write the startupcache's data // to disk if the timer hasn't already gone off. void MaybeInitShutdownWrite();
// For use during shutdown - ensure we complete the shutdown write // before shutdown, even in the FastShutdown case. void EnsureShutdownWriteComplete();
// Signal that data should not be loaded from the cache file staticvoid IgnoreDiskCache();
staticbool GetIgnoreDiskCache();
// In DEBUG builds, returns a stream that will attempt to check for // and disallow multiple writes of the same object.
nsresult GetDebugObjectOutputStream(nsIObjectOutputStream* aStream,
nsIObjectOutputStream** outStream);
// This measures all the heap memory used by the StartupCache, i.e. it // excludes the mapping.
size_t HeapSizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const
MOZ_REQUIRES(mTableLock);
// Returns a file pointer for the cache file with the given name in the // current profile.
Result<nsCOMPtr<nsIFile>, nsresult> GetCacheFile(const nsAString& suffix);
// Opens the cache file for reading.
Result<Ok, nsresult> OpenCache();
// Writes the cache to disk
Result<Ok, nsresult> WriteToDisk() MOZ_REQUIRES(mTableLock);
// This is normally accessed on MainThread, but WriteToDisk() can // access it on other threads
HashMap<nsCString, StartupCacheEntry> mTable MOZ_GUARDED_BY(mTableLock); // This owns references to the contents of tables which have been invalidated. // In theory it grows forever if the cache is continually filled and then // invalidated, but this should not happen in practice. Deleting old tables // could create dangling pointers. RefPtrs could be introduced, but it would // be a large amount of error-prone work to change.
nsTArray<decltype(mTable)> mOldTables MOZ_GUARDED_BY(mTableLock);
size_t mAllowedInvalidationsCount;
nsCOMPtr<nsIFile> mFile;
mozilla::loader::AutoMemMap mCacheData MOZ_GUARDED_BY(mTableLock);
Mutex mTableLock;
// This debug outputstream attempts to detect if clients are writing multiple // references to the same object. We only support that if that object // is a singleton. #ifdef DEBUG class StartupCacheDebugOutputStream final : public nsIObjectOutputStream {
~StartupCacheDebugOutputStream() = default;
Die Informationen auf dieser Webseite wurden
nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit,
noch Qualität der bereit gestellten Informationen zugesichert.
Bemerkung:
Die farbliche Syntaxdarstellung ist noch experimentell.
