From e1b2f2ef09f06ffb890fa52db5cd5ce50dd4bfe8 Mon Sep 17 00:00:00 2001
From: Bill McCloskey <billm@mozilla.com>
Date: Wed, 1 Feb 2017 14:08:46 -0800
Subject: [PATCH] Bug 1337537 - Make a SystemGroup singleton (r=ehsan)

MozReview-Commit-ID: Jnwrr49daeM
---
 xpcom/build/XPCOMInit.cpp     | 10 +++++
 xpcom/threads/SystemGroup.cpp | 76 +++++++++++++++++++++++++++++++++--
 xpcom/threads/SystemGroup.h   | 11 ++++-
 3 files changed, 93 insertions(+), 4 deletions(-)

diff --git a/xpcom/build/XPCOMInit.cpp b/xpcom/build/XPCOMInit.cpp
index e30220c9f410..71c1988c9d8c 100644
--- a/xpcom/build/XPCOMInit.cpp
+++ b/xpcom/build/XPCOMInit.cpp
@@ -130,6 +130,7 @@ extern nsresult nsStringInputStreamConstructor(nsISupports*, REFNSIID, void**);
 #include "mozilla/Services.h"
 #include "mozilla/Omnijar.h"
 #include "mozilla/HangMonitor.h"
+#include "mozilla/SystemGroup.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/BackgroundHangMonitor.h"
 
@@ -553,6 +554,9 @@ NS_InitXPCOM2(nsIServiceManager** aResult,
     return rv;
   }
 
+  // Init the SystemGroup for dispatching main thread runnables.
+  SystemGroup::InitStatic();
+
   // Set up the timer globals/timer thread
   rv = nsTimerImpl::Startup();
   if (NS_WARN_IF(NS_FAILED(rv))) {
@@ -786,6 +790,9 @@ NS_InitMinimalXPCOM()
     return rv;
   }
 
+  // Init the SystemGroup for dispatching main thread runnables.
+  SystemGroup::InitStatic();
+
   // Set up the timer globals/timer thread.
   rv = nsTimerImpl::Startup();
   if (NS_WARN_IF(NS_FAILED(rv))) {
@@ -1065,6 +1072,9 @@ ShutdownXPCOM(nsIServiceManager* aServMgr)
   nsComponentManagerImpl::gComponentManager = nullptr;
   nsCategoryManager::Destroy();
 
+  // Shut down SystemGroup for main thread dispatching.
+  SystemGroup::Shutdown();
+
   NS_ShutdownAtomTable();
 
   NS_IF_RELEASE(gDebug);
diff --git a/xpcom/threads/SystemGroup.cpp b/xpcom/threads/SystemGroup.cpp
index c0641f1afcc3..c67bb6e454c0 100644
--- a/xpcom/threads/SystemGroup.cpp
+++ b/xpcom/threads/SystemGroup.cpp
@@ -7,21 +7,91 @@
 #include "SystemGroup.h"
 
 #include "mozilla/Move.h"
+#include "mozilla/UniquePtr.h"
 #include "nsINamed.h"
 
 using namespace mozilla;
 
+class SystemGroupImpl final : public ValidatingDispatcher
+{
+public:
+  SystemGroupImpl();
+  ~SystemGroupImpl() {}
+
+  static void InitStatic();
+  static void ShutdownStatic();
+  static SystemGroupImpl* Get();
+
+  NS_METHOD_(MozExternalRefCountType) AddRef(void)
+  {
+    return 2;
+  }
+  NS_METHOD_(MozExternalRefCountType) Release(void)
+  {
+    return 1;
+  }
+
+private:
+  static UniquePtr<SystemGroupImpl> sSingleton;
+};
+
+UniquePtr<SystemGroupImpl> SystemGroupImpl::sSingleton;
+
+SystemGroupImpl::SystemGroupImpl()
+{
+  CreateEventTargets(/* aNeedValidation = */ true);
+}
+
+/* static */ void
+SystemGroupImpl::InitStatic()
+{
+  MOZ_ASSERT(!sSingleton);
+  MOZ_ASSERT(NS_IsMainThread());
+  sSingleton = MakeUnique<SystemGroupImpl>();
+}
+
+/* static */ void
+SystemGroupImpl::ShutdownStatic()
+{
+  sSingleton->Shutdown();
+  sSingleton = nullptr;
+}
+
+/* static */ SystemGroupImpl*
+SystemGroupImpl::Get()
+{
+  MOZ_ASSERT(sSingleton);
+  return sSingleton.get();
+}
+
+void
+SystemGroup::InitStatic()
+{
+  SystemGroupImpl::InitStatic();
+}
+
+void
+SystemGroup::Shutdown()
+{
+  SystemGroupImpl::ShutdownStatic();
+}
+
 /* static */ nsresult
 SystemGroup::Dispatch(const char* aName,
                       TaskCategory aCategory,
                       already_AddRefed<nsIRunnable>&& aRunnable)
 {
-  return Dispatcher::UnlabeledDispatch(aName, aCategory, Move(aRunnable));
+  return SystemGroupImpl::Get()->Dispatch(aName, aCategory, Move(aRunnable));
 }
 
 /* static */ nsIEventTarget*
 SystemGroup::EventTargetFor(TaskCategory aCategory)
 {
-  nsCOMPtr<nsIEventTarget> main = do_GetMainThread();
-  return main;
+  return SystemGroupImpl::Get()->EventTargetFor(aCategory);
+}
+
+/* static */ AbstractThread*
+SystemGroup::AbstractMainThreadFor(TaskCategory aCategory)
+{
+  return SystemGroupImpl::Get()->AbstractMainThreadFor(aCategory);
 }
diff --git a/xpcom/threads/SystemGroup.h b/xpcom/threads/SystemGroup.h
index d27eba268e56..1e94b7c25815 100644
--- a/xpcom/threads/SystemGroup.h
+++ b/xpcom/threads/SystemGroup.h
@@ -8,6 +8,7 @@
 #define mozilla_SystemGroup_h
 
 #include "mozilla/TaskCategory.h"
+#include "mozilla/Dispatcher.h"
 
 // The SystemGroup should be used for dispatching runnables that don't need to
 // touch web content. Runnables dispatched to the SystemGroup are run in order
@@ -16,7 +17,8 @@
 
 namespace mozilla {
 
-class SystemGroup {
+class SystemGroup
+{
  public:
   // This method is safe to use from any thread.
   static nsresult Dispatch(const char* aName,
@@ -25,6 +27,13 @@ class SystemGroup {
 
   // This method is safe to use from any thread.
   static nsIEventTarget* EventTargetFor(TaskCategory aCategory);
+
+  // Must be called on the main thread. The AbstractThread can always be used
+  // off the main thread.
+  static AbstractThread* AbstractMainThreadFor(TaskCategory aCategory);
+
+  static void InitStatic();
+  static void Shutdown();
 };
 
 } // namespace mozilla