1 files changed, 129 insertions, 0 deletions
diff --git a/ipc/mscom/EnsureMTA.h b/ipc/mscom/EnsureMTA.h
new file mode 100644
index 0000000000..662192c476
--- /dev/null
+++ b/ipc/mscom/EnsureMTA.h
@@ -0,0 +1,129 @@
+/* -*- 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/. */
+
+#ifndef mozilla_mscom_EnsureMTA_h
+#define mozilla_mscom_EnsureMTA_h
+
+#include "MainThreadUtils.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/MozPromise.h"
+#include "mozilla/Unused.h"
+#include "mozilla/mscom/AgileReference.h"
+#include "mozilla/mscom/Utils.h"
+#include "mozilla/RefPtr.h"
+#include "nsCOMPtr.h"
+#include "nsIThread.h"
+#include "nsThreadUtils.h"
+#include "nsWindowsHelpers.h"
+
+#include <windows.h>
+
+namespace mozilla {
+namespace mscom {
+namespace detail {
+
+// Forward declarations
+template <typename T>
+struct MTADelete;
+
+template <typename T>
+struct MTARelease;
+
+template <typename T>
+struct MTAReleaseInChildProcess;
+
+struct PreservedStreamDeleter;
+
+}  // namespace detail
+
+class ProcessRuntime;
+
+// This class is OK to use as a temporary on the stack.
+class MOZ_STACK_CLASS EnsureMTA final {
+ public:
+  enum class Option {
+    Default,
+    // Forcibly dispatch to the thread returned by GetPersistentMTAThread(),
+    // even if the current thread is already inside a MTA.
+    ForceDispatchToPersistentThread,
+  };
+
+  /**
+   * Synchronously run |aClosure| on a thread living in the COM multithreaded
+   * apartment. If the current thread lives inside the COM MTA, then it runs
+   * |aClosure| immediately unless |aOpt| ==
+   * Option::ForceDispatchToPersistentThread.
+   */
+  template <typename FuncT>
+  explicit EnsureMTA(FuncT&& aClosure, Option aOpt = Option::Default) {
+    if (aOpt != Option::ForceDispatchToPersistentThread &&
+        IsCurrentThreadMTA()) {
+      // We're already on the MTA, we can run aClosure directly
+      aClosure();
+      return;
+    }
+
+    // In this case we need to run aClosure on a background thread in the MTA
+    nsCOMPtr<nsIRunnable> runnable(
+        NS_NewRunnableFunction("EnsureMTA::EnsureMTA", std::move(aClosure)));
+    SyncDispatch(std::move(runnable), aOpt);
+  }
+
+ private:
+  static nsCOMPtr<nsIThread> GetPersistentMTAThread();
+
+  static void SyncDispatch(nsCOMPtr<nsIRunnable>&& aRunnable, Option aOpt);
+  static void SyncDispatchToPersistentThread(nsIRunnable* aRunnable);
+
+  // The following function is private in order to force any consumers to be
+  // declared as friends of EnsureMTA. The intention is to prevent
+  // AsyncOperation from becoming some kind of free-for-all mechanism for
+  // asynchronously executing work on a background thread.
+  template <typename FuncT>
+  static void AsyncOperation(FuncT&& aClosure) {
+    if (IsCurrentThreadMTA()) {
+      aClosure();
+      return;
+    }
+
+    nsCOMPtr<nsIThread> thread(GetPersistentMTAThread());
+    MOZ_ASSERT(thread);
+    if (!thread) {
+      return;
+    }
+
+    DebugOnly<nsresult> rv = thread->Dispatch(
+        NS_NewRunnableFunction("mscom::EnsureMTA::AsyncOperation",
+                               std::move(aClosure)),
+        NS_DISPATCH_NORMAL);
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+  }
+
+  /**
+   * This constructor just ensures that the MTA is up and running. This should
+   * only be called by ProcessRuntime.
+   */
+  EnsureMTA();
+
+  friend class mozilla::mscom::ProcessRuntime;
+
+  template <typename T>
+  friend struct mozilla::mscom::detail::MTADelete;
+
+  template <typename T>
+  friend struct mozilla::mscom::detail::MTARelease;
+
+  template <typename T>
+  friend struct mozilla::mscom::detail::MTAReleaseInChildProcess;
+
+  friend struct mozilla::mscom::detail::PreservedStreamDeleter;
+};
+
+}  // namespace mscom
+}  // namespace mozilla
+
+#endif  // mozilla_mscom_EnsureMTA_h