1 files changed, 151 insertions, 0 deletions
diff --git a/ipc/mscom/EnsureMTA.cpp b/ipc/mscom/EnsureMTA.cpp
new file mode 100644
index 0000000000..4950664c6c
--- /dev/null
+++ b/ipc/mscom/EnsureMTA.cpp
@@ -0,0 +1,151 @@
+/* -*- 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/mscom/EnsureMTA.h"
+
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/mscom/Utils.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/StaticLocalPtr.h"
+#include "nsThreadUtils.h"
+
+#include "private/pprthred.h"
+
+namespace {
+
+class EnterMTARunnable : public mozilla::Runnable {
+ public:
+  EnterMTARunnable() : mozilla::Runnable("EnterMTARunnable") {}
+  NS_IMETHOD Run() override {
+    mozilla::DebugOnly<HRESULT> hr =
+        ::CoInitializeEx(nullptr, COINIT_MULTITHREADED);
+    MOZ_ASSERT(SUCCEEDED(hr));
+    return NS_OK;
+  }
+};
+
+class BackgroundMTAData {
+ public:
+  BackgroundMTAData() {
+    nsCOMPtr<nsIRunnable> runnable = new EnterMTARunnable();
+    mozilla::DebugOnly<nsresult> rv =
+        NS_NewNamedThread("COM MTA", getter_AddRefs(mThread), runnable);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "NS_NewNamedThread failed");
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+  }
+
+  ~BackgroundMTAData() {
+    if (mThread) {
+      mThread->Dispatch(
+          NS_NewRunnableFunction("BackgroundMTAData::~BackgroundMTAData",
+                                 &::CoUninitialize),
+          NS_DISPATCH_NORMAL);
+      mThread->Shutdown();
+    }
+  }
+
+  nsCOMPtr<nsIThread> GetThread() const { return mThread; }
+
+ private:
+  nsCOMPtr<nsIThread> mThread;
+};
+
+}  // anonymous namespace
+
+namespace mozilla {
+namespace mscom {
+
+/* static */
+RefPtr<EnsureMTA::CreateInstanceAgileRefPromise>
+EnsureMTA::CreateInstanceInternal(REFCLSID aClsid, REFIID aIid) {
+  MOZ_ASSERT(IsCurrentThreadExplicitMTA());
+
+  RefPtr<IUnknown> iface;
+  HRESULT hr = ::CoCreateInstance(aClsid, nullptr, CLSCTX_INPROC_SERVER, aIid,
+                                  getter_AddRefs(iface));
+  if (FAILED(hr)) {
+    return CreateInstanceAgileRefPromise::CreateAndReject(hr, __func__);
+  }
+
+  // We need to use the two argument constructor for AgileReference because our
+  // RefPtr is not parameterized on the specific interface being requested.
+  AgileReference agileRef(aIid, iface);
+  if (!agileRef) {
+    return CreateInstanceAgileRefPromise::CreateAndReject(agileRef.GetHResult(),
+                                                          __func__);
+  }
+
+  return CreateInstanceAgileRefPromise::CreateAndResolve(std::move(agileRef),
+                                                         __func__);
+}
+
+/* static */
+RefPtr<EnsureMTA::CreateInstanceAgileRefPromise> EnsureMTA::CreateInstance(
+    REFCLSID aClsid, REFIID aIid) {
+  MOZ_ASSERT(IsCOMInitializedOnCurrentThread());
+
+  const bool isClassOk = IsClassThreadAwareInprocServer(aClsid);
+  MOZ_ASSERT(isClassOk,
+             "mozilla::mscom::EnsureMTA::CreateInstance is not "
+             "safe/performant/necessary to use with this CLSID. This CLSID "
+             "either does not support creation from within a multithreaded "
+             "apartment, or it is not an in-process server.");
+  if (!isClassOk) {
+    return CreateInstanceAgileRefPromise::CreateAndReject(CO_E_NOT_SUPPORTED,
+                                                          __func__);
+  }
+
+  if (IsCurrentThreadExplicitMTA()) {
+    // It's safe to immediately call CreateInstanceInternal
+    return CreateInstanceInternal(aClsid, aIid);
+  }
+
+  // aClsid and aIid are references. Make local copies that we can put into the
+  // lambda in case the sources of aClsid or aIid are not static data
+  CLSID localClsid = aClsid;
+  IID localIid = aIid;
+
+  auto invoker = [localClsid,
+                  localIid]() -> RefPtr<CreateInstanceAgileRefPromise> {
+    return CreateInstanceInternal(localClsid, localIid);
+  };
+
+  nsCOMPtr<nsIThread> mtaThread(GetMTAThread());
+
+  return InvokeAsync(mtaThread->SerialEventTarget(), __func__,
+                     std::move(invoker));
+}
+
+/* static */
+nsCOMPtr<nsIThread> EnsureMTA::GetMTAThread() {
+  static StaticLocalAutoPtr<BackgroundMTAData> sMTAData(
+      []() -> BackgroundMTAData* {
+        BackgroundMTAData* bgData = new BackgroundMTAData();
+
+        auto setClearOnShutdown = [ptr = &sMTAData]() -> void {
+          ClearOnShutdown(ptr, ShutdownPhase::ShutdownThreads);
+        };
+
+        if (NS_IsMainThread()) {
+          setClearOnShutdown();
+          return bgData;
+        }
+
+        SchedulerGroup::Dispatch(
+            TaskCategory::Other,
+            NS_NewRunnableFunction("mscom::EnsureMTA::GetMTAThread",
+                                   std::move(setClearOnShutdown)));
+
+        return bgData;
+      }());
+
+  MOZ_ASSERT(sMTAData);
+
+  return sMTAData->GetThread();
+}
+
+}  // namespace mscom
+}  // namespace mozilla