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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 */
#ifndef StartupCache_h_
#define StartupCache_h_
#include <utility>
#include "nsClassHashtable.h"
#include "nsComponentManagerUtils.h"
#include "nsTArray.h"
#include "nsTHashSet.h"
#include "nsTStringHasher.h" // mozilla::DefaultHasher<nsCString>
#include "nsZipArchive.h"
#include "nsITimer.h"
#include "nsIMemoryReporter.h"
#include "nsIObserverService.h"
#include "nsIObserver.h"
#include "nsIObjectOutputStream.h"
#include "nsIFile.h"
#include "mozilla/Attributes.h"
#include "mozilla/AutoMemMap.h"
#include "mozilla/Compression.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Monitor.h"
#include "mozilla/Mutex.h"
#include "mozilla/Result.h"
#include "mozilla/UniquePtr.h"
#include "mozilla/UniquePtrExtensions.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 StartupCacheEntry {
UniqueFreePtr<char[]> mData;
uint32_t mOffset;
uint32_t mCompressedSize;
uint32_t mUncompressedSize;
int32_t mHeaderOffsetInFile;
int32_t mRequestedOrder;
bool mRequested;
MOZ_IMPLICIT StartupCacheEntry(uint32_t aOffset, uint32_t aCompressedSize,
uint32_t aUncompressedSize)
: mData(nullptr),
mRequested(false) {}
StartupCacheEntry(UniqueFreePtr<char[]> aData, size_t aLength,
int32_t aRequestedOrder)
: mData(std::move(aData)),
mRequested(true) {}
// 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) {}
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;
class StartupCache : public nsIMemoryReporter {
friend class 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(const char* id);
// Returns a buffer that was previously stored, caller does not take ownership
nsresult GetBuffer(const char* id, const char** outbuf, uint32_t* length);
// Stores a buffer. Caller yields ownership.
nsresult PutBuffer(const char* id, UniqueFreePtr<char[]>&& inbuf,
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
static void IgnoreDiskCache();
static bool 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);
static StartupCache* GetSingletonNoInit();
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
bool ShouldCompactCache() MOZ_REQUIRES(mTableLock);
nsresult ResetStartupWriteTimerCheckingReadCount();
nsresult ResetStartupWriteTimerAndLock();
nsresult ResetStartupWriteTimer() MOZ_REQUIRES(mTableLock);
bool StartupWriteComplete();
virtual ~StartupCache();
friend class StartupCacheInfo;
Result<Ok, nsresult> LoadArchive() MOZ_REQUIRES(mTableLock);
nsresult Init();
// 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);
void WaitOnPrefetch();
void StartPrefetchMemory() MOZ_REQUIRES(mTableLock);
static nsresult InitSingleton();
static void WriteTimeout(nsITimer* aTimer, void* aClosure);
void MaybeWriteOffMainThread();
void ThreadedPrefetch(uint8_t* aStart, size_t aSize);
Monitor mPrefetchComplete{"StartupCachePrefetch"};
bool mPrefetchInProgress MOZ_GUARDED_BY(mPrefetchComplete){false};
// 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;
nsCOMPtr<nsIObserverService> mObserverService;
RefPtr<StartupCacheListener> mListener;
nsCOMPtr<nsITimer> mTimer;
bool mDirty MOZ_GUARDED_BY(mTableLock);
bool mWrittenOnce MOZ_GUARDED_BY(mTableLock);
bool mCurTableReferenced MOZ_GUARDED_BY(mTableLock);
uint32_t mRequestedCount;
size_t mCacheEntriesBaseOffset;
static StaticRefPtr<StartupCache> gStartupCache;
static bool gShutdownInitiated;
static bool gIgnoreDiskCache;
static bool gFoundDiskCacheOnInit;
UniquePtr<Compression::LZ4FrameDecompressionContext> mDecompressionContext;
#ifdef DEBUG
nsTHashSet<nsCOMPtr<nsISupports>> mWriteObjectMap;
// 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;
StartupCacheDebugOutputStream(nsIObjectOutputStream* binaryStream,
nsTHashSet<nsCOMPtr<nsISupports>>* objectMap)
: mBinaryStream(binaryStream), mObjectMap(objectMap) {}
bool CheckReferences(nsISupports* aObject);
nsCOMPtr<nsIObjectOutputStream> mBinaryStream;
nsTHashSet<nsCOMPtr<nsISupports>>* mObjectMap;
#endif // DEBUG
} // namespace scache
} // namespace mozilla
#endif // StartupCache_h_