Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 956 insertions, 0 deletions

diff --git a/startupcache/StartupCache.cpp b/startupcache/StartupCache.cpp
new file mode 100644
index 0000000000..9c066a1951
--- /dev/null
+++ b/startupcache/StartupCache.cpp
@@ -0,0 +1,956 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#include "prio.h"
+#include "PLDHashTable.h"
+#include "mozilla/IOInterposer.h"
+#include "mozilla/AutoMemMap.h"
+#include "mozilla/IOBuffers.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/MemUtils.h"
+#include "mozilla/MmapFaultHandler.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/scache/StartupCache.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/Try.h"
+
+#include "nsClassHashtable.h"
+#include "nsComponentManagerUtils.h"
+#include "nsCRT.h"
+#include "nsDirectoryServiceUtils.h"
+#include "nsIClassInfo.h"
+#include "nsIFile.h"
+#include "nsIObserver.h"
+#include "nsIOutputStream.h"
+#include "nsISupports.h"
+#include "nsITimer.h"
+#include "mozilla/Omnijar.h"
+#include "prenv.h"
+#include "mozilla/Telemetry.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+#include "nsIProtocolHandler.h"
+#include "GeckoProfiler.h"
+#include "nsAppRunner.h"
+#include "xpcpublic.h"
+#ifdef MOZ_BACKGROUNDTASKS
+#  include "mozilla/BackgroundTasks.h"
+#endif
+
+#if defined(XP_WIN)
+#  include <windows.h>
+#endif
+
+#ifdef IS_BIG_ENDIAN
+#  define SC_ENDIAN "big"
+#else
+#  define SC_ENDIAN "little"
+#endif
+
+#if PR_BYTES_PER_WORD == 4
+#  define SC_WORDSIZE "4"
+#else
+#  define SC_WORDSIZE "8"
+#endif
+
+using namespace mozilla::Compression;
+
+namespace mozilla {
+namespace scache {
+
+MOZ_DEFINE_MALLOC_SIZE_OF(StartupCacheMallocSizeOf)
+
+NS_IMETHODIMP
+StartupCache::CollectReports(nsIHandleReportCallback* aHandleReport,
+                             nsISupports* aData, bool aAnonymize) {
+  MutexAutoLock lock(mTableLock);
+  MOZ_COLLECT_REPORT(
+      "explicit/startup-cache/mapping", KIND_NONHEAP, UNITS_BYTES,
+      mCacheData.nonHeapSizeOfExcludingThis(),
+      "Memory used to hold the mapping of the startup cache from file. "
+      "This memory is likely to be swapped out shortly after start-up.");
+
+  MOZ_COLLECT_REPORT("explicit/startup-cache/data", KIND_HEAP, UNITS_BYTES,
+                     HeapSizeOfIncludingThis(StartupCacheMallocSizeOf),
+                     "Memory used by the startup cache for things other than "
+                     "the file mapping.");
+
+  return NS_OK;
+}
+
+static const uint8_t MAGIC[] = "startupcache0002";
+// This is a heuristic value for how much to reserve for mTable to avoid
+// rehashing. This is not a hard limit in release builds, but it is in
+// debug builds as it should be stable. If we exceed this number we should
+// just increase it.
+static const size_t STARTUP_CACHE_RESERVE_CAPACITY = 450;
+// This is a hard limit which we will assert on, to ensure that we don't
+// have some bug causing runaway cache growth.
+static const size_t STARTUP_CACHE_MAX_CAPACITY = 5000;
+
+// Not const because we change it for gtests.
+static uint8_t STARTUP_CACHE_WRITE_TIMEOUT = 60;
+
+#define STARTUP_CACHE_NAME "startupCache." SC_WORDSIZE "." SC_ENDIAN
+
+static inline Result<Ok, nsresult> Write(PRFileDesc* fd, const void* data,
+                                         int32_t len) {
+  if (PR_Write(fd, data, len) != len) {
+    return Err(NS_ERROR_FAILURE);
+  }
+  return Ok();
+}
+
+static inline Result<Ok, nsresult> Seek(PRFileDesc* fd, int32_t offset) {
+  if (PR_Seek(fd, offset, PR_SEEK_SET) == -1) {
+    return Err(NS_ERROR_FAILURE);
+  }
+  return Ok();
+}
+
+static nsresult MapLZ4ErrorToNsresult(size_t aError) {
+  return NS_ERROR_FAILURE;
+}
+
+StartupCache* StartupCache::GetSingletonNoInit() {
+  return StartupCache::gStartupCache;
+}
+
+StartupCache* StartupCache::GetSingleton() {
+#ifdef MOZ_BACKGROUNDTASKS
+  if (BackgroundTasks::IsBackgroundTaskMode()) {
+    return nullptr;
+  }
+#endif
+
+  if (!gStartupCache) {
+    if (!XRE_IsParentProcess()) {
+      return nullptr;
+    }
+#ifdef MOZ_DISABLE_STARTUPCACHE
+    return nullptr;
+#else
+    StartupCache::InitSingleton();
+#endif
+  }
+
+  return StartupCache::gStartupCache;
+}
+
+void StartupCache::DeleteSingleton() { StartupCache::gStartupCache = nullptr; }
+
+nsresult StartupCache::InitSingleton() {
+  nsresult rv;
+  StartupCache::gStartupCache = new StartupCache();
+
+  rv = StartupCache::gStartupCache->Init();
+  if (NS_FAILED(rv)) {
+    StartupCache::gStartupCache = nullptr;
+  }
+  return rv;
+}
+
+StaticRefPtr<StartupCache> StartupCache::gStartupCache;
+bool StartupCache::gShutdownInitiated;
+bool StartupCache::gIgnoreDiskCache;
+bool StartupCache::gFoundDiskCacheOnInit;
+
+NS_IMPL_ISUPPORTS(StartupCache, nsIMemoryReporter)
+
+StartupCache::StartupCache()
+    : mTableLock("StartupCache::mTableLock"),
+      mDirty(false),
+      mWrittenOnce(false),
+      mCurTableReferenced(false),
+      mRequestedCount(0),
+      mCacheEntriesBaseOffset(0) {}
+
+StartupCache::~StartupCache() { UnregisterWeakMemoryReporter(this); }
+
+nsresult StartupCache::Init() {
+  // workaround for bug 653936
+  nsCOMPtr<nsIProtocolHandler> jarInitializer(
+      do_GetService(NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "jar"));
+
+  nsresult rv;
+
+  if (mozilla::RunningGTest()) {
+    STARTUP_CACHE_WRITE_TIMEOUT = 3;
+  }
+
+  // This allows to override the startup cache filename
+  // which is useful from xpcshell, when there is no ProfLDS directory to keep
+  // cache in.
+  char* env = PR_GetEnv("MOZ_STARTUP_CACHE");
+  if (env && *env) {
+    rv = NS_NewLocalFile(NS_ConvertUTF8toUTF16(env), false,
+                         getter_AddRefs(mFile));
+  } else {
+    nsCOMPtr<nsIFile> file;
+    rv = NS_GetSpecialDirectory("ProfLDS", getter_AddRefs(file));
+    if (NS_FAILED(rv)) {
+      // return silently, this will fail in mochitests's xpcshell process.
+      return rv;
+    }
+
+    rv = file->AppendNative("startupCache"_ns);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // Try to create the directory if it's not there yet
+    rv = file->Create(nsIFile::DIRECTORY_TYPE, 0777);
+    if (NS_FAILED(rv) && rv != NS_ERROR_FILE_ALREADY_EXISTS) return rv;
+
+    rv = file->AppendNative(nsLiteralCString(STARTUP_CACHE_NAME));
+
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    mFile = file;
+  }
+
+  NS_ENSURE_TRUE(mFile, NS_ERROR_UNEXPECTED);
+
+  mObserverService = do_GetService("@mozilla.org/observer-service;1");
+
+  if (!mObserverService) {
+    NS_WARNING("Could not get observerService.");
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  mListener = new StartupCacheListener();
+  rv = mObserverService->AddObserver(mListener, NS_XPCOM_SHUTDOWN_OBSERVER_ID,
+                                     false);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = mObserverService->AddObserver(mListener, "startupcache-invalidate",
+                                     false);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = mObserverService->AddObserver(mListener, "intl:app-locales-changed",
+                                     false);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  {
+    MutexAutoLock lock(mTableLock);
+    auto result = LoadArchive();
+    rv = result.isErr() ? result.unwrapErr() : NS_OK;
+  }
+
+  gFoundDiskCacheOnInit = rv != NS_ERROR_FILE_NOT_FOUND;
+
+  // Sometimes we don't have a cache yet, that's ok.
+  // If it's corrupted, just remove it and start over.
+  if (gIgnoreDiskCache || (NS_FAILED(rv) && rv != NS_ERROR_FILE_NOT_FOUND)) {
+    NS_WARNING("Failed to load startupcache file correctly, removing!");
+    InvalidateCache();
+  }
+
+  RegisterWeakMemoryReporter(this);
+  mDecompressionContext = MakeUnique<LZ4FrameDecompressionContext>(true);
+
+  return NS_OK;
+}
+
+void StartupCache::StartPrefetchMemory() {
+  {
+    MonitorAutoLock lock(mPrefetchComplete);
+    mPrefetchInProgress = true;
+  }
+  NS_DispatchBackgroundTask(NewRunnableMethod<uint8_t*, size_t>(
+      "StartupCache::ThreadedPrefetch", this, &StartupCache::ThreadedPrefetch,
+      mCacheData.get<uint8_t>().get(), mCacheData.size()));
+}
+
+/**
+ * LoadArchive can only be called from the main thread.
+ */
+Result<Ok, nsresult> StartupCache::LoadArchive() {
+  MOZ_ASSERT(NS_IsMainThread(), "Can only load startup cache on main thread");
+  if (gIgnoreDiskCache) return Err(NS_ERROR_FAILURE);
+
+  MOZ_TRY(mCacheData.init(mFile));
+  auto size = mCacheData.size();
+  if (CanPrefetchMemory()) {
+    StartPrefetchMemory();
+  }
+
+  uint32_t headerSize;
+  if (size < sizeof(MAGIC) + sizeof(headerSize)) {
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+
+  auto data = mCacheData.get<uint8_t>();
+  auto end = data + size;
+
+  MMAP_FAULT_HANDLER_BEGIN_BUFFER(data.get(), size)
+
+  if (memcmp(MAGIC, data.get(), sizeof(MAGIC))) {
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+  data += sizeof(MAGIC);
+
+  headerSize = LittleEndian::readUint32(data.get());
+  data += sizeof(headerSize);
+
+  if (headerSize > end - data) {
+    MOZ_ASSERT(false, "StartupCache file is corrupt.");
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+
+  Range<uint8_t> header(data, data + headerSize);
+  data += headerSize;
+
+  mCacheEntriesBaseOffset = sizeof(MAGIC) + sizeof(headerSize) + headerSize;
+  {
+    if (!mTable.reserve(STARTUP_CACHE_RESERVE_CAPACITY)) {
+      return Err(NS_ERROR_UNEXPECTED);
+    }
+    auto cleanup = MakeScopeExit([&]() {
+      mTableLock.AssertCurrentThreadOwns();
+      WaitOnPrefetch();
+      mTable.clear();
+      mCacheData.reset();
+    });
+    loader::InputBuffer buf(header);
+
+    uint32_t currentOffset = 0;
+    while (!buf.finished()) {
+      uint32_t offset = 0;
+      uint32_t compressedSize = 0;
+      uint32_t uncompressedSize = 0;
+      nsCString key;
+      buf.codeUint32(offset);
+      buf.codeUint32(compressedSize);
+      buf.codeUint32(uncompressedSize);
+      buf.codeString(key);
+
+      if (offset + compressedSize > end - data) {
+        MOZ_ASSERT(false, "StartupCache file is corrupt.");
+        return Err(NS_ERROR_UNEXPECTED);
+      }
+
+      // Make sure offsets match what we'd expect based on script ordering and
+      // size, as a basic sanity check.
+      if (offset != currentOffset) {
+        return Err(NS_ERROR_UNEXPECTED);
+      }
+      currentOffset += compressedSize;
+
+      // We could use mTable.putNew if we knew the file we're loading weren't
+      // corrupt. However, we don't know that, so check if the key already
+      // exists. If it does, we know the file must be corrupt.
+      decltype(mTable)::AddPtr p = mTable.lookupForAdd(key);
+      if (p) {
+        return Err(NS_ERROR_UNEXPECTED);
+      }
+
+      if (!mTable.add(
+              p, key,
+              StartupCacheEntry(offset, compressedSize, uncompressedSize))) {
+        return Err(NS_ERROR_UNEXPECTED);
+      }
+    }
+
+    if (buf.error()) {
+      return Err(NS_ERROR_UNEXPECTED);
+    }
+
+    cleanup.release();
+  }
+
+  MMAP_FAULT_HANDLER_CATCH(Err(NS_ERROR_UNEXPECTED))
+
+  return Ok();
+}
+
+bool StartupCache::HasEntry(const char* id) {
+  AUTO_PROFILER_LABEL("StartupCache::HasEntry", OTHER);
+
+  MOZ_ASSERT(NS_IsMainThread(), "Startup cache only available on main thread");
+
+  MutexAutoLock lock(mTableLock);
+  return mTable.has(nsDependentCString(id));
+}
+
+nsresult StartupCache::GetBuffer(const char* id, const char** outbuf,
+                                 uint32_t* length)
+    MOZ_NO_THREAD_SAFETY_ANALYSIS {
+  AUTO_PROFILER_LABEL("StartupCache::GetBuffer", OTHER);
+
+  NS_ASSERTION(NS_IsMainThread(),
+               "Startup cache only available on main thread");
+
+  Telemetry::LABELS_STARTUP_CACHE_REQUESTS label =
+      Telemetry::LABELS_STARTUP_CACHE_REQUESTS::Miss;
+  auto telemetry =
+      MakeScopeExit([&label] { Telemetry::AccumulateCategorical(label); });
+
+  MutexAutoLock lock(mTableLock);
+  decltype(mTable)::Ptr p = mTable.lookup(nsDependentCString(id));
+  if (!p) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  auto& value = p->value();
+  if (value.mData) {
+    label = Telemetry::LABELS_STARTUP_CACHE_REQUESTS::HitMemory;
+  } else {
+    if (!mCacheData.initialized()) {
+      return NS_ERROR_NOT_AVAILABLE;
+    }
+    // It is impossible for a write to be pending here. This is because
+    // we just checked mCacheData.initialized(), and this is reset before
+    // writing to the cache. It's not re-initialized unless we call
+    // LoadArchive(), either from Init() (which must have already happened) or
+    // InvalidateCache(). InvalidateCache() locks the mutex, so a write can't be
+    // happening.
+    // Also, WriteToDisk() requires mTableLock, so while it's writing we can't
+    // be here.
+
+    size_t totalRead = 0;
+    size_t totalWritten = 0;
+    Span<const char> compressed = Span(
+        mCacheData.get<char>().get() + mCacheEntriesBaseOffset + value.mOffset,
+        value.mCompressedSize);
+    value.mData = UniqueFreePtr<char[]>(reinterpret_cast<char*>(
+        malloc(sizeof(char) * value.mUncompressedSize)));
+    Span<char> uncompressed = Span(value.mData.get(), value.mUncompressedSize);
+    MMAP_FAULT_HANDLER_BEGIN_BUFFER(uncompressed.Elements(),
+                                    uncompressed.Length())
+    bool finished = false;
+    while (!finished) {
+      auto result = mDecompressionContext->Decompress(
+          uncompressed.From(totalWritten), compressed.From(totalRead));
+      if (NS_WARN_IF(result.isErr())) {
+        value.mData = nullptr;
+        MutexAutoUnlock unlock(mTableLock);
+        InvalidateCache();
+        return NS_ERROR_FAILURE;
+      }
+      auto decompressionResult = result.unwrap();
+      totalRead += decompressionResult.mSizeRead;
+      totalWritten += decompressionResult.mSizeWritten;
+      finished = decompressionResult.mFinished;
+    }
+
+    MMAP_FAULT_HANDLER_CATCH(NS_ERROR_FAILURE)
+
+    label = Telemetry::LABELS_STARTUP_CACHE_REQUESTS::HitDisk;
+  }
+
+  if (!value.mRequested) {
+    value.mRequested = true;
+    value.mRequestedOrder = ++mRequestedCount;
+    MOZ_ASSERT(mRequestedCount <= mTable.count(),
+               "Somehow we requested more StartupCache items than exist.");
+    ResetStartupWriteTimerCheckingReadCount();
+  }
+
+  // Track that something holds a reference into mTable, so we know to hold
+  // onto it in case the cache is invalidated.
+  mCurTableReferenced = true;
+  *outbuf = value.mData.get();
+  *length = value.mUncompressedSize;
+  return NS_OK;
+}
+
+// Makes a copy of the buffer, client retains ownership of inbuf.
+nsresult StartupCache::PutBuffer(const char* id, UniqueFreePtr<char[]>&& inbuf,
+                                 uint32_t len) MOZ_NO_THREAD_SAFETY_ANALYSIS {
+  NS_ASSERTION(NS_IsMainThread(),
+               "Startup cache only available on main thread");
+  if (StartupCache::gShutdownInitiated) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  // Try to gain the table write lock. If the background task to write the
+  // cache is running, this will fail.
+  MutexAutoTryLock lock(mTableLock);
+  if (!lock) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+  mTableLock.AssertCurrentThreadOwns();
+  bool exists = mTable.has(nsDependentCString(id));
+  if (exists) {
+    NS_WARNING("Existing entry in StartupCache.");
+    // Double-caching is undesirable but not an error.
+    return NS_OK;
+  }
+
+  // putNew returns false on alloc failure - in the very unlikely event we hit
+  // that and aren't going to crash elsewhere, there's no reason we need to
+  // crash here.
+  if (mTable.putNew(nsCString(id), StartupCacheEntry(std::move(inbuf), len,
+                                                     ++mRequestedCount))) {
+    return ResetStartupWriteTimer();
+  }
+  MOZ_DIAGNOSTIC_ASSERT(mTable.count() < STARTUP_CACHE_MAX_CAPACITY,
+                        "Too many StartupCache entries.");
+  return NS_OK;
+}
+
+size_t StartupCache::HeapSizeOfIncludingThis(
+    mozilla::MallocSizeOf aMallocSizeOf) const {
+  // This function could measure more members, but they haven't been found by
+  // DMD to be significant.  They can be added later if necessary.
+
+  size_t n = aMallocSizeOf(this);
+
+  n += mTable.shallowSizeOfExcludingThis(aMallocSizeOf);
+  for (auto iter = mTable.iter(); !iter.done(); iter.next()) {
+    if (iter.get().value().mData) {
+      n += aMallocSizeOf(iter.get().value().mData.get());
+    }
+    n += iter.get().key().SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+  }
+
+  return n;
+}
+
+/**
+ * WriteToDisk writes the cache out to disk. Callers of WriteToDisk need to call
+ * WaitOnWriteComplete to make sure there isn't a write
+ * happening on another thread.
+ * We own the mTableLock here.
+ */
+Result<Ok, nsresult> StartupCache::WriteToDisk() {
+  if (!mDirty || mWrittenOnce) {
+    return Ok();
+  }
+
+  if (!mFile) {
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+
+  AutoFDClose raiiFd;
+  MOZ_TRY(mFile->OpenNSPRFileDesc(PR_WRONLY | PR_CREATE_FILE | PR_TRUNCATE,
+                                  0644, getter_Transfers(raiiFd)));
+  const auto fd = raiiFd.get();
+
+  nsTArray<StartupCacheEntry::KeyValuePair> entries(mTable.count());
+  for (auto iter = mTable.iter(); !iter.done(); iter.next()) {
+    if (iter.get().value().mRequested) {
+      StartupCacheEntry::KeyValuePair kv(&iter.get().key(),
+                                         &iter.get().value());
+      entries.AppendElement(kv);
+    }
+  }
+
+  if (entries.IsEmpty()) {
+    return Ok();
+  }
+
+  entries.Sort(StartupCacheEntry::Comparator());
+  loader::OutputBuffer buf;
+  for (auto& e : entries) {
+    auto* key = e.first;
+    auto* value = e.second;
+    auto uncompressedSize = value->mUncompressedSize;
+    // Set the mHeaderOffsetInFile so we can go back and edit the offset.
+    value->mHeaderOffsetInFile = buf.cursor();
+    // Write a 0 offset/compressed size as a placeholder until we get the real
+    // offset after compressing.
+    buf.codeUint32(0);
+    buf.codeUint32(0);
+    buf.codeUint32(uncompressedSize);
+    buf.codeString(*key);
+  }
+
+  uint8_t headerSize[4];
+  LittleEndian::writeUint32(headerSize, buf.cursor());
+
+  MOZ_TRY(Write(fd, MAGIC, sizeof(MAGIC)));
+  MOZ_TRY(Write(fd, headerSize, sizeof(headerSize)));
+  size_t headerStart = sizeof(MAGIC) + sizeof(headerSize);
+  size_t dataStart = headerStart + buf.cursor();
+  MOZ_TRY(Seek(fd, dataStart));
+
+  size_t offset = 0;
+
+  const size_t chunkSize = 1024 * 16;
+  LZ4FrameCompressionContext ctx(6,         /* aCompressionLevel */
+                                 chunkSize, /* aReadBufLen */
+                                 true,      /* aChecksum */
+                                 true);     /* aStableSrc */
+  size_t writeBufLen = ctx.GetRequiredWriteBufferLength();
+  auto writeBuffer = MakeUnique<char[]>(writeBufLen);
+  auto writeSpan = Span(writeBuffer.get(), writeBufLen);
+
+  for (auto& e : entries) {
+    auto value = e.second;
+    value->mOffset = offset;
+    Span<const char> result;
+    MOZ_TRY_VAR(result,
+                ctx.BeginCompressing(writeSpan).mapErr(MapLZ4ErrorToNsresult));
+    MOZ_TRY(Write(fd, result.Elements(), result.Length()));
+    offset += result.Length();
+
+    for (size_t i = 0; i < value->mUncompressedSize; i += chunkSize) {
+      size_t size = std::min(chunkSize, value->mUncompressedSize - i);
+      char* uncompressed = value->mData.get() + i;
+      MOZ_TRY_VAR(result, ctx.ContinueCompressing(Span(uncompressed, size))
+                              .mapErr(MapLZ4ErrorToNsresult));
+      MOZ_TRY(Write(fd, result.Elements(), result.Length()));
+      offset += result.Length();
+    }
+
+    MOZ_TRY_VAR(result, ctx.EndCompressing().mapErr(MapLZ4ErrorToNsresult));
+    MOZ_TRY(Write(fd, result.Elements(), result.Length()));
+    offset += result.Length();
+    value->mCompressedSize = offset - value->mOffset;
+    MOZ_TRY(Seek(fd, dataStart + offset));
+  }
+
+  for (auto& e : entries) {
+    auto value = e.second;
+    uint8_t* headerEntry = buf.Get() + value->mHeaderOffsetInFile;
+    LittleEndian::writeUint32(headerEntry, value->mOffset);
+    LittleEndian::writeUint32(headerEntry + sizeof(value->mOffset),
+                              value->mCompressedSize);
+  }
+  MOZ_TRY(Seek(fd, headerStart));
+  MOZ_TRY(Write(fd, buf.Get(), buf.cursor()));
+
+  mDirty = false;
+  mWrittenOnce = true;
+
+  return Ok();
+}
+
+void StartupCache::InvalidateCache(bool memoryOnly) {
+  WaitOnPrefetch();
+  // Ensure we're not writing using mTable...
+  MutexAutoLock lock(mTableLock);
+
+  mWrittenOnce = false;
+  if (memoryOnly) {
+    // This should only be called in tests.
+    auto writeResult = WriteToDisk();
+    if (NS_WARN_IF(writeResult.isErr())) {
+      gIgnoreDiskCache = true;
+      return;
+    }
+  }
+  if (mCurTableReferenced) {
+    // There should be no way for this assert to fail other than a user manually
+    // sending startupcache-invalidate messages through the Browser Toolbox. If
+    // something knowingly invalidates the cache, the event can be counted with
+    // mAllowedInvalidationsCount.
+    MOZ_DIAGNOSTIC_ASSERT(
+        xpc::IsInAutomation() ||
+            // The allowed invalidations can grow faster than the old tables, so
+            // guard against incorrect unsigned subtraction.
+            mAllowedInvalidationsCount > mOldTables.Length() ||
+            // Now perform the real check.
+            mOldTables.Length() - mAllowedInvalidationsCount < 10,
+        "Startup cache invalidated too many times.");
+    mOldTables.AppendElement(std::move(mTable));
+    mCurTableReferenced = false;
+  } else {
+    mTable.clear();
+  }
+  mRequestedCount = 0;
+  if (!memoryOnly) {
+    mCacheData.reset();
+    nsresult rv = mFile->Remove(false);
+    if (NS_FAILED(rv) && rv != NS_ERROR_FILE_NOT_FOUND) {
+      gIgnoreDiskCache = true;
+      return;
+    }
+  }
+  gIgnoreDiskCache = false;
+  auto result = LoadArchive();
+  if (NS_WARN_IF(result.isErr())) {
+    gIgnoreDiskCache = true;
+  }
+}
+
+void StartupCache::CountAllowedInvalidation() { mAllowedInvalidationsCount++; }
+
+void StartupCache::MaybeInitShutdownWrite() {
+  if (mTimer) {
+    mTimer->Cancel();
+  }
+  gShutdownInitiated = true;
+
+  MaybeWriteOffMainThread();
+}
+
+void StartupCache::EnsureShutdownWriteComplete() {
+  MutexAutoLock lock(mTableLock);
+  // If we've already written or there's nothing to write,
+  // we don't need to do anything. This is the common case.
+  if (mWrittenOnce || (mCacheData.initialized() && !ShouldCompactCache())) {
+    return;
+  }
+  // Otherwise, ensure the write happens. The timer should have been cancelled
+  // already in MaybeInitShutdownWrite.
+
+  // We got the lock. Keep the following in sync with
+  // MaybeWriteOffMainThread:
+  WaitOnPrefetch();
+  mDirty = true;
+  mCacheData.reset();
+  // Most of this should be redundant given MaybeWriteOffMainThread should
+  // have run before now.
+
+  auto writeResult = WriteToDisk();
+  Unused << NS_WARN_IF(writeResult.isErr());
+  // We've had the lock, and `WriteToDisk()` sets mWrittenOnce and mDirty
+  // when done, and checks for them when starting, so we don't need to do
+  // anything else.
+}
+
+void StartupCache::IgnoreDiskCache() {
+  gIgnoreDiskCache = true;
+  if (gStartupCache) gStartupCache->InvalidateCache();
+}
+
+bool StartupCache::GetIgnoreDiskCache() { return gIgnoreDiskCache; }
+
+void StartupCache::WaitOnPrefetch() {
+  // This can't be called from within ThreadedPrefetch()
+  MonitorAutoLock lock(mPrefetchComplete);
+  while (mPrefetchInProgress) {
+    mPrefetchComplete.Wait();
+  }
+}
+
+void StartupCache::ThreadedPrefetch(uint8_t* aStart, size_t aSize) {
+  // Always notify of completion, even if MMAP_FAULT_HANDLER_CATCH()
+  // early-returns.
+  auto notifyPrefetchComplete = MakeScopeExit([&] {
+    MonitorAutoLock lock(mPrefetchComplete);
+    mPrefetchInProgress = false;
+    mPrefetchComplete.NotifyAll();
+  });
+
+  // PrefetchMemory does madvise/equivalent, but doesn't access the memory
+  // pointed to by aStart
+  MMAP_FAULT_HANDLER_BEGIN_BUFFER(aStart, aSize)
+  PrefetchMemory(aStart, aSize);
+  MMAP_FAULT_HANDLER_CATCH()
+}
+
+// mTableLock must be held
+bool StartupCache::ShouldCompactCache() {
+  // If we've requested less than 4/5 of the startup cache, then we should
+  // probably compact it down. This can happen quite easily after the first run,
+  // which seems to request quite a few more things than subsequent runs.
+  CheckedInt<uint32_t> threshold = CheckedInt<uint32_t>(mTable.count()) * 4 / 5;
+  MOZ_RELEASE_ASSERT(threshold.isValid(), "Runaway StartupCache size");
+  return mRequestedCount < threshold.value();
+}
+
+/*
+ * The write-thread is spawned on a timeout(which is reset with every write).
+ * This can avoid a slow shutdown.
+ */
+void StartupCache::WriteTimeout(nsITimer* aTimer, void* aClosure) {
+  /*
+   * It is safe to use the pointer passed in aClosure to reference the
+   * StartupCache object because the timer's lifetime is tightly coupled to
+   * the lifetime of the StartupCache object; this timer is canceled in the
+   * StartupCache destructor, guaranteeing that this function runs if and only
+   * if the StartupCache object is valid.
+   */
+  StartupCache* startupCacheObj = static_cast<StartupCache*>(aClosure);
+  startupCacheObj->MaybeWriteOffMainThread();
+}
+
+/*
+ * See StartupCache::WriteTimeout above - this is just the non-static body.
+ */
+void StartupCache::MaybeWriteOffMainThread() {
+  {
+    MutexAutoLock lock(mTableLock);
+    if (mWrittenOnce || (mCacheData.initialized() && !ShouldCompactCache())) {
+      return;
+    }
+  }
+  // Keep this code in sync with EnsureShutdownWriteComplete.
+  WaitOnPrefetch();
+  {
+    MutexAutoLock lock(mTableLock);
+    mDirty = true;
+    mCacheData.reset();
+  }
+
+  RefPtr<StartupCache> self = this;
+  nsCOMPtr<nsIRunnable> runnable =
+      NS_NewRunnableFunction("StartupCache::Write", [self]() mutable {
+        MutexAutoLock lock(self->mTableLock);
+        auto result = self->WriteToDisk();
+        Unused << NS_WARN_IF(result.isErr());
+      });
+  NS_DispatchBackgroundTask(runnable.forget(), NS_DISPATCH_EVENT_MAY_BLOCK);
+}
+
+// We don't want to refcount StartupCache, so we'll just
+// hold a ref to this and pass it to observerService instead.
+NS_IMPL_ISUPPORTS(StartupCacheListener, nsIObserver)
+
+nsresult StartupCacheListener::Observe(nsISupports* subject, const char* topic,
+                                       const char16_t* data) {
+  StartupCache* sc = StartupCache::GetSingleton();
+  if (!sc) return NS_OK;
+
+  if (strcmp(topic, NS_XPCOM_SHUTDOWN_OBSERVER_ID) == 0) {
+    // Do not leave the thread running past xpcom shutdown
+    sc->WaitOnPrefetch();
+    StartupCache::gShutdownInitiated = true;
+    // Note that we don't do anything special for the background write
+    // task; we expect the threadpool to finish running any tasks already
+    // posted to it prior to shutdown. FastShutdown will call
+    // EnsureShutdownWriteComplete() to ensure any pending writes happen
+    // in that case.
+  } else if (strcmp(topic, "startupcache-invalidate") == 0) {
+    sc->InvalidateCache(data && nsCRT::strcmp(data, u"memoryOnly") == 0);
+  } else if (strcmp(topic, "intl:app-locales-changed") == 0) {
+    // Live language switching invalidates the startup cache due to the history
+    // sidebar retaining localized strings in its internal SQL query. This
+    // should be a relatively rare event, but a user could do it an arbitrary
+    // number of times.
+    sc->CountAllowedInvalidation();
+  }
+  return NS_OK;
+}
+
+nsresult StartupCache::GetDebugObjectOutputStream(
+    nsIObjectOutputStream* aStream, nsIObjectOutputStream** aOutStream) {
+  NS_ENSURE_ARG_POINTER(aStream);
+#ifdef DEBUG
+  auto* stream = new StartupCacheDebugOutputStream(aStream, &mWriteObjectMap);
+  NS_ADDREF(*aOutStream = stream);
+#else
+  NS_ADDREF(*aOutStream = aStream);
+#endif
+
+  return NS_OK;
+}
+
+nsresult StartupCache::ResetStartupWriteTimerCheckingReadCount() {
+  nsresult rv = NS_OK;
+  if (!mTimer)
+    mTimer = NS_NewTimer();
+  else
+    rv = mTimer->Cancel();
+  NS_ENSURE_SUCCESS(rv, rv);
+  // Wait for the specified timeout, then write out the cache.
+  mTimer->InitWithNamedFuncCallback(
+      StartupCache::WriteTimeout, this, STARTUP_CACHE_WRITE_TIMEOUT * 1000,
+      nsITimer::TYPE_ONE_SHOT, "StartupCache::WriteTimeout");
+  return NS_OK;
+}
+
+// For test code only
+nsresult StartupCache::ResetStartupWriteTimerAndLock() {
+  MutexAutoLock lock(mTableLock);
+  return ResetStartupWriteTimer();
+}
+
+nsresult StartupCache::ResetStartupWriteTimer() {
+  mDirty = true;
+  nsresult rv = NS_OK;
+  if (!mTimer)
+    mTimer = NS_NewTimer();
+  else
+    rv = mTimer->Cancel();
+  NS_ENSURE_SUCCESS(rv, rv);
+  // Wait for the specified timeout, then write out the cache.
+  mTimer->InitWithNamedFuncCallback(
+      StartupCache::WriteTimeout, this, STARTUP_CACHE_WRITE_TIMEOUT * 1000,
+      nsITimer::TYPE_ONE_SHOT, "StartupCache::WriteTimeout");
+  return NS_OK;
+}
+
+// Used only in tests:
+bool StartupCache::StartupWriteComplete() {
+  // Need to have written to disk and not added new things since;
+  MutexAutoLock lock(mTableLock);
+  return !mDirty && mWrittenOnce;
+}
+
+// StartupCacheDebugOutputStream implementation
+#ifdef DEBUG
+NS_IMPL_ISUPPORTS(StartupCacheDebugOutputStream, nsIObjectOutputStream,
+                  nsIBinaryOutputStream, nsIOutputStream)
+
+bool StartupCacheDebugOutputStream::CheckReferences(nsISupports* aObject) {
+  nsresult rv;
+
+  nsCOMPtr<nsIClassInfo> classInfo = do_QueryInterface(aObject);
+  if (!classInfo) {
+    NS_ERROR("aObject must implement nsIClassInfo");
+    return false;
+  }
+
+  uint32_t flags;
+  rv = classInfo->GetFlags(&flags);
+  NS_ENSURE_SUCCESS(rv, false);
+  if (flags & nsIClassInfo::SINGLETON) return true;
+
+  bool inserted = mObjectMap->EnsureInserted(aObject);
+  if (!inserted) {
+    NS_ERROR(
+        "non-singleton aObject is referenced multiple times in this"
+        "serialization, we don't support that.");
+  }
+
+  return inserted;
+}
+
+// nsIObjectOutputStream implementation
+nsresult StartupCacheDebugOutputStream::WriteObject(nsISupports* aObject,
+                                                    bool aIsStrongRef) {
+  nsCOMPtr<nsISupports> rootObject(do_QueryInterface(aObject));
+
+  NS_ASSERTION(rootObject.get() == aObject,
+               "bad call to WriteObject -- call WriteCompoundObject!");
+  bool check = CheckReferences(aObject);
+  NS_ENSURE_TRUE(check, NS_ERROR_FAILURE);
+  return mBinaryStream->WriteObject(aObject, aIsStrongRef);
+}
+
+nsresult StartupCacheDebugOutputStream::WriteSingleRefObject(
+    nsISupports* aObject) {
+  nsCOMPtr<nsISupports> rootObject(do_QueryInterface(aObject));
+
+  NS_ASSERTION(rootObject.get() == aObject,
+               "bad call to WriteSingleRefObject -- call WriteCompoundObject!");
+  bool check = CheckReferences(aObject);
+  NS_ENSURE_TRUE(check, NS_ERROR_FAILURE);
+  return mBinaryStream->WriteSingleRefObject(aObject);
+}
+
+nsresult StartupCacheDebugOutputStream::WriteCompoundObject(
+    nsISupports* aObject, const nsIID& aIID, bool aIsStrongRef) {
+  nsCOMPtr<nsISupports> rootObject(do_QueryInterface(aObject));
+
+  nsCOMPtr<nsISupports> roundtrip;
+  rootObject->QueryInterface(aIID, getter_AddRefs(roundtrip));
+  NS_ASSERTION(roundtrip.get() == aObject,
+               "bad aggregation or multiple inheritance detected by call to "
+               "WriteCompoundObject!");
+
+  bool check = CheckReferences(aObject);
+  NS_ENSURE_TRUE(check, NS_ERROR_FAILURE);
+  return mBinaryStream->WriteCompoundObject(aObject, aIID, aIsStrongRef);
+}
+
+nsresult StartupCacheDebugOutputStream::WriteID(nsID const& aID) {
+  return mBinaryStream->WriteID(aID);
+}
+
+char* StartupCacheDebugOutputStream::GetBuffer(uint32_t aLength,
+                                               uint32_t aAlignMask) {
+  return mBinaryStream->GetBuffer(aLength, aAlignMask);
+}
+
+void StartupCacheDebugOutputStream::PutBuffer(char* aBuffer, uint32_t aLength) {
+  mBinaryStream->PutBuffer(aBuffer, aLength);
+}
+#endif  // DEBUG
+
+}  // namespace scache
+}  // namespace mozilla