gecko-dev/startupcache/StartupCache.h

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/* -*- 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/. */
#ifndef StartupCache_h_
#define StartupCache_h_
#include "nsClassHashtable.h"
#include "nsComponentManagerUtils.h"
#include "nsTArray.h"
#include "nsZipArchive.h"
#include "nsITimer.h"
#include "nsIMemoryReporter.h"
#include "nsIObserverService.h"
#include "nsIObserver.h"
#include "nsIObjectOutputStream.h"
#include "nsIOutputStream.h"
#include "nsIFile.h"
#include "mozilla/Attributes.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/UniquePtr.h"
/**
* 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.
*/
namespace mozilla {
namespace scache {
struct CacheEntry {
UniquePtr<char[]> data;
uint32_t size;
CacheEntry() : size(0) {}
// Takes possession of buf
CacheEntry(UniquePtr<char[]> buf, uint32_t len)
: data(std::move(buf)), size(len) {}
~CacheEntry() {}
size_t SizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) {
return mallocSizeOf(this) + mallocSizeOf(data.get());
}
};
// 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() {}
NS_DECL_THREADSAFE_ISUPPORTS
NS_DECL_NSIOBSERVER
};
class StartupCache : public nsIMemoryReporter {
friend class StartupCacheListener;
public:
NS_DECL_THREADSAFE_ISUPPORTS
NS_DECL_NSIMEMORYREPORTER
// StartupCache methods. See above comments for a more detailed description.
// Returns a buffer that was previously stored, caller takes ownership.
nsresult GetBuffer(const char* id, UniquePtr<char[]>* outbuf,
uint32_t* length);
// Stores a buffer. Caller yields ownership.
nsresult PutBuffer(const char* id, UniquePtr<char[]>&& inbuf,
uint32_t length);
// Removes the cache file.
void InvalidateCache(bool memoryOnly = false);
// Signal that data should not be loaded from the cache file
static void IgnoreDiskCache();
// 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);
static StartupCache* GetSingleton();
static void DeleteSingleton();
// This measures all the heap memory used by the StartupCache, i.e. it
// excludes the mapping.
size_t HeapSizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
size_t SizeOfMapping();
// FOR TESTING ONLY
nsresult ResetStartupWriteTimer();
bool StartupWriteComplete();
private:
StartupCache();
virtual ~StartupCache();
nsresult LoadArchive();
nsresult Init();
void WriteToDisk();
void WaitOnWriteThread();
static nsresult InitSingleton();
static void WriteTimeout(nsITimer* aTimer, void* aClosure);
static void ThreadedWrite(void* aClosure);
nsClassHashtable<nsCStringHashKey, CacheEntry> mTable;
nsTArray<nsCString> mPendingWrites;
RefPtr<nsZipArchive> mArchive;
nsCOMPtr<nsIFile> mFile;
nsCOMPtr<nsIObserverService> mObserverService;
RefPtr<StartupCacheListener> mListener;
nsCOMPtr<nsITimer> mTimer;
bool mStartupWriteInitiated;
static StaticRefPtr<StartupCache> gStartupCache;
static bool gShutdownInitiated;
static bool gIgnoreDiskCache;
PRThread* mWriteThread;
#ifdef DEBUG
nsTHashtable<nsISupportsHashKey> mWriteObjectMap;
#endif
};
// 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() {}
NS_DECL_ISUPPORTS
NS_DECL_NSIOBJECTOUTPUTSTREAM
StartupCacheDebugOutputStream(nsIObjectOutputStream* binaryStream,
nsTHashtable<nsISupportsHashKey>* objectMap)
: mBinaryStream(binaryStream), mObjectMap(objectMap) {}
NS_FORWARD_SAFE_NSIBINARYOUTPUTSTREAM(mBinaryStream)
NS_FORWARD_SAFE_NSIOUTPUTSTREAM(mBinaryStream)
bool CheckReferences(nsISupports* aObject);
nsCOMPtr<nsIObjectOutputStream> mBinaryStream;
nsTHashtable<nsISupportsHashKey>* mObjectMap;
};
#endif // DEBUG
} // namespace scache
} // namespace mozilla
#endif // StartupCache_h_