Bug 1840515 - Step 2: Preload the omnijars in the fork server. r=nika

This extends the previous support for `-greomni` and `-appomni` to the
fork server, so that it can pre-open the jar files and thus continue
using the correct versions in forked child processes even if the files on
disk are replaced by an update or deleted.

Differential Revision: https://phabricator.services.mozilla.com/D185331

dom/ipc/ContentProcess.cpp

@@ -151,8 +151,11 @@ bool ContentProcess::Init(int aArgc, char* aArgv[]) {
     return false;
   }
 
-  // Handle the -greomni/-appomni flags
-  Omnijar::ChildProcessInit(aArgc, aArgv);
+  // Handle the -greomni/-appomni flags (unless the forkserver already
+  // preloaded the jar(s)).
+  if (!Omnijar::IsInitialized()) {
+    Omnijar::ChildProcessInit(aArgc, aArgv);
+  }
 
   rv = NS_InitXPCOM(nullptr, xpcomAppDir, &mDirProvider);
   if (NS_FAILED(rv)) {

ipc/glue/ForkServer.cpp

@@ -1,21 +1,24 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* vim: set ts=8 sts=4 et sw=4 tw=80: */
+/* -*- 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 "mozilla/ipc/ForkServer.h"
-#include "mozilla/Logging.h"
+
 #include "chrome/common/chrome_switches.h"
+#include "ipc/IPCMessageUtilsSpecializations.h"
 #include "mozilla/BlockingResourceBase.h"
-#include "mozilla/ipc/ProtocolMessageUtils.h"
+#include "mozilla/Logging.h"
+#include "mozilla/Omnijar.h"
 #include "mozilla/ipc/FileDescriptor.h"
 #include "mozilla/ipc/IPDLParamTraits.h"
-#include "ipc/IPCMessageUtilsSpecializations.h"
+#include "mozilla/ipc/ProtocolMessageUtils.h"
 #include "nsTraceRefcnt.h"
 
+#include <fcntl.h>
 #include <string.h>
 #include <unistd.h>
-#include <fcntl.h>
 
 #if defined(XP_LINUX) && defined(MOZ_SANDBOX)
 #  include "mozilla/SandboxLaunch.h"
@@ -40,6 +43,16 @@ void ForkServer::InitProcess(int* aArgc, char*** aArgv) {
                                        DataBufferClear::AfterReceiving);
 }
 
+/**
+ * Preload any resources that the forked child processes might need,
+ * and which might change incompatibly or become unavailable by the
+ * time they're started.  For example: the omnijar files, or certain
+ * shared libraries.
+ */
+static void ForkServerPreload(int& aArgc, char** aArgv) {
+  Omnijar::ChildProcessInit(aArgc, aArgv);
+}
+
 /**
  * Start providing the service at the IPC channel.
  */
@@ -251,6 +264,7 @@ bool ForkServer::RunForkServer(int* aArgc, char*** aArgv) {
   XRE_SetProcessType("forkserver");
   NS_LogInit();
   mozilla::LogModule::Init(0, nullptr);
+  ForkServerPreload(*aArgc, *aArgv);
   MOZ_LOG(gForkServiceLog, LogLevel::Verbose, ("Start a fork server"));
   {
     DebugOnly<base::ProcessHandle> forkserver_pid = base::GetCurrentProcId();

ipc/glue/GeckoChildProcessHost.cpp

@@ -1255,7 +1255,9 @@ Result<Ok, LaunchError> PosixProcessLauncher::DoSetup() {
 
   mChildArgv.insert(mChildArgv.end(), mExtraOpts.begin(), mExtraOpts.end());
 
-  if (mProcessType == GeckoProcessType_Content && Omnijar::IsInitialized()) {
+  if ((mProcessType == GeckoProcessType_Content ||
+       mProcessType == GeckoProcessType_ForkServer) &&
+      Omnijar::IsInitialized()) {
     // Make sure that child processes can find the omnijar, if they
     // use full XPCOM.  See Omnijar::ChildProcessInit and its callers.
     nsAutoCString path;