gecko-dev/ipc/mscom/EnsureMTA.h

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C
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/* -*- 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/Unused.h"
#include "mozilla/mscom/COMApartmentRegion.h"
#include "mozilla/mscom/Utils.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;
}
// This class is OK to use as a temporary on the stack.
class MOZ_STACK_CLASS EnsureMTA final
{
public:
/**
* This constructor just ensures that the MTA thread is up and running.
*/
EnsureMTA()
{
MOZ_ASSERT(NS_IsMainThread());
nsCOMPtr<nsIThread> thread = GetMTAThread();
MOZ_ASSERT(thread);
Unused << thread;
}
template <typename FuncT>
explicit EnsureMTA(const FuncT& aClosure)
{
if (IsCurrentThreadMTA()) {
// We're already on the MTA, we can run aClosure directly
aClosure();
return;
}
MOZ_ASSERT(NS_IsMainThread());
// In this case we need to run aClosure on a background thread in the MTA
nsCOMPtr<nsIThread> thread = GetMTAThread();
MOZ_ASSERT(thread);
if (!thread) {
return;
}
// Note that we might reenter the EnsureMTA constructor while we wait on
// this event due to APC dispatch, therefore we need a unique event object
// for each entry. If perf becomes an issue then we will want to maintain
// an array of events where the Nth event is unique to the Nth reentry.
nsAutoHandle event(::CreateEventW(nullptr, FALSE, FALSE, nullptr));
if (!event) {
return;
}
HANDLE eventHandle = event.get();
auto eventSetter = [&aClosure, eventHandle]() -> void {
aClosure();
::SetEvent(eventHandle);
};
nsresult rv =
thread->Dispatch(NS_NewRunnableFunction("EnsureMTA", eventSetter), NS_DISPATCH_NORMAL);
MOZ_ASSERT(NS_SUCCEEDED(rv));
if (NS_FAILED(rv)) {
return;
}
DWORD waitResult;
while ((waitResult = ::WaitForSingleObjectEx(event, INFINITE, TRUE)) ==
WAIT_IO_COMPLETION) {
}
MOZ_ASSERT(waitResult == WAIT_OBJECT_0);
}
private:
static nsCOMPtr<nsIThread> GetMTAThread();
// 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(const FuncT& aClosure)
{
if (IsCurrentThreadMTA()) {
aClosure();
return;
}
nsCOMPtr<nsIThread> thread(GetMTAThread());
MOZ_ASSERT(thread);
if (!thread) {
return;
}
DebugOnly<nsresult> rv = thread->Dispatch(
NS_NewRunnableFunction("mscom::EnsureMTA::AsyncOperation",
aClosure), NS_DISPATCH_NORMAL);
MOZ_ASSERT(NS_SUCCEEDED(rv));
}
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