From 26a029d407be480d791972afb5975cf62c9360a6 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Fri, 19 Apr 2024 02:47:55 +0200 Subject: Adding upstream version 124.0.1. Signed-off-by: Daniel Baumann --- xpcom/threads/WinHandleWatcher.cpp | 306 +++++++++++++++++++++++++++++++++++++ 1 file changed, 306 insertions(+) create mode 100644 xpcom/threads/WinHandleWatcher.cpp (limited to 'xpcom/threads/WinHandleWatcher.cpp') diff --git a/xpcom/threads/WinHandleWatcher.cpp b/xpcom/threads/WinHandleWatcher.cpp new file mode 100644 index 0000000000..d475993925 --- /dev/null +++ b/xpcom/threads/WinHandleWatcher.cpp @@ -0,0 +1,306 @@ +/* -*- 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 +#include + +#include "mozilla/AlreadyAddRefed.h" +#include "mozilla/Assertions.h" +#include "mozilla/Logging.h" +#include "mozilla/Mutex.h" +#include "mozilla/RefPtr.h" +#include "mozilla/ThreadSafety.h" +#include "mozilla/WinHandleWatcher.h" + +#include "nsCOMPtr.h" +#include "nsIRunnable.h" +#include "nsISerialEventTarget.h" +#include "nsISupportsImpl.h" +#include "nsITargetShutdownTask.h" +#include "nsIWeakReferenceUtils.h" +#include "nsThreadUtils.h" + +mozilla::LazyLogModule sHWLog("HandleWatcher"); + +namespace mozilla { +namespace details { +struct WaitHandleDeleter { + void operator()(PTP_WAIT waitHandle) { + MOZ_LOG(sHWLog, LogLevel::Debug, ("Closing PTP_WAIT %p", waitHandle)); + ::CloseThreadpoolWait(waitHandle); + } +}; +} // namespace details +using WaitHandlePtr = UniquePtr; + +// HandleWatcher::Impl +// +// The backing implementation of HandleWatcher is a PTP_WAIT, an OS-threadpool +// wait-object. Windows doesn't actually create a new thread per wait-object; +// OS-threadpool threads are assigned to wait-objects only when their associated +// handle become signaled -- although explicit documentation of this fact is +// somewhat obscurely placed. [1] +// +// Throughout this class, we use manual locking and unlocking guarded by Clang's +// thread-safety warnings, rather than scope-based lock-guards. See `Replace()` +// for an explanation and justification. +// +// [1]https://learn.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-waitformultipleobjects#remarks +class HandleWatcher::Impl final : public nsITargetShutdownTask { + NS_DECL_THREADSAFE_ISUPPORTS + + public: + Impl() = default; + + private: + ~Impl() { MOZ_ASSERT(IsStopped()); } + + struct Data { + // The watched handle and its callback. + HANDLE handle; + RefPtr target; + nsCOMPtr runnable; + + // Handle to the threadpool wait-object. + WaitHandlePtr waitHandle; + // A pointer to ourselves, notionally owned by the wait-object. + RefPtr self; + + // (We can't actually do this because a) it has annoying consequences in + // C++20 thanks to P1008R1, and b) Clang just ignores it anyway.) + // + // ~Data() MOZ_EXCLUDES(mMutex) = default; + }; + + mozilla::Mutex mMutex{"HandleWatcher::Impl"}; + Data mData MOZ_GUARDED_BY(mMutex) = {}; + + // Callback from OS threadpool wait-object. + static void CALLBACK WaitCallback(PTP_CALLBACK_INSTANCE, void* ctx, + PTP_WAIT aWaitHandle, + TP_WAIT_RESULT aResult) { + static_cast(ctx)->OnWaitCompleted(aWaitHandle, aResult); + } + + void OnWaitCompleted(PTP_WAIT aWaitHandle, TP_WAIT_RESULT aResult) + MOZ_EXCLUDES(mMutex) { + MOZ_ASSERT(aResult == WAIT_OBJECT_0); + + mMutex.Lock(); + // If this callback is no longer the active callback, skip out. + // All cleanup is someone else's problem. + if (aWaitHandle != mData.waitHandle.get()) { + MOZ_LOG(sHWLog, LogLevel::Debug, + ("Recv'd already-stopped callback: HW %p | PTP_WAIT %p", this, + aWaitHandle)); + mMutex.Unlock(); + return; + } + + // Take our self-pointer so that we release it on exit. + RefPtr self = std::move(mData.self); + + MOZ_LOG(sHWLog, LogLevel::Info, + ("Recv'd callback: HW %p | handle %p | target %p | PTP_WAIT %p", + this, mData.handle, mData.target.get(), aWaitHandle)); + + // This may fail if (for example) `mData.target` is being shut down, but we + // have not yet received the shutdown callback. + mData.target->Dispatch(mData.runnable.forget()); + Replace(Data{}); + } + + public: + static RefPtr Create(HANDLE aHandle, nsIEventTarget* aTarget, + already_AddRefed aRunnable) { + auto impl = MakeRefPtr(); + bool const ok [[maybe_unused]] = + impl->Watch(aHandle, aTarget, std::move(aRunnable)); + MOZ_ASSERT(ok); + return impl; + } + + private: + bool Watch(HANDLE aHandle, nsIEventTarget* aTarget, + already_AddRefed aRunnable) MOZ_EXCLUDES(mMutex) { + MOZ_ASSERT(aHandle); + MOZ_ASSERT(aTarget); + + RefPtr target(aTarget); + + WaitHandlePtr waitHandle{ + ::CreateThreadpoolWait(&WaitCallback, this, nullptr)}; + if (!waitHandle) { + return false; + } + + { + mMutex.Lock(); + + nsresult const ret = aTarget->RegisterShutdownTask(this); + if (NS_FAILED(ret)) { + mMutex.Unlock(); + return false; + } + + MOZ_LOG(sHWLog, LogLevel::Info, + ("Setting callback: HW %p | handle %p | target %p | PTP_WAIT %p", + this, aHandle, aTarget, waitHandle.get())); + + // returns `void`; presumably always succeeds given a successful + // `::CreateThreadpoolWait()` + ::SetThreadpoolWait(waitHandle.get(), aHandle, nullptr); + // After this point, you must call `FlushWaitHandle(waitHandle.get())` + // before destroying the wait handle. (Note that this must be done while + // *not* holding `mMutex`!) + + Replace(Data{.handle = aHandle, + .target = std::move(target), + .runnable = aRunnable, + .waitHandle = std::move(waitHandle), + .self = this}); + } + + return true; + } + + void TargetShutdown() MOZ_EXCLUDES(mMutex) override final { + mMutex.Lock(); + + MOZ_LOG(sHWLog, LogLevel::Debug, + ("Target shutdown: HW %p | handle %p | target %p | PTP_WAIT %p", + this, mData.handle, mData.target.get(), mData.waitHandle.get())); + + // Clear mData.target, since there's no need to unregister the shutdown task + // anymore. Hold onto it until we release the mutex, though, to avoid any + // reentrancy issues. + // + // This is more for internal consistency than safety: someone has to be + // shutting `target` down, and that someone isn't us, so there's necessarily + // another reference out there. (Although decrementing the refcount might + // still have arbitrary effects if someone's been excessively clever with + // nsISupports::Release...) + auto const oldTarget = std::move(mData.target); + Replace(Data{}); + // (Static-assert that the mutex has indeed been released.) + ([&]() MOZ_EXCLUDES(mMutex) {})(); + } + + public: + void Stop() MOZ_EXCLUDES(mMutex) { + mMutex.Lock(); + Replace(Data{}); + } + + bool IsStopped() MOZ_EXCLUDES(mMutex) { + mozilla::MutexAutoLock lock(mMutex); + return !mData.handle; + } + + private: + // Throughout this class, we use manual locking and unlocking guarded by + // Clang's thread-safety warnings, rather than scope-based lock-guards. This + // is largely driven by `Replace()`, below, which performs both operations + // which require the mutex to be held and operations which require it to not + // be held, and therefore must explicitly sequence the mutex release. + // + // These explicit locks, unlocks, and annotations are both alien to C++ and + // offensively tedious; but they _are_ still checked for state consistency at + // scope boundaries. (The concerned reader is invited to test this by + // deliberately removing an `mMutex.Unlock()` call from anywhere in the class + // and viewing the resultant compiler diagnostics.) + // + // A more principled, or at least differently-principled, implementation might + // create a scope-based lock-guard and pass it to `Replace()` to dispose of at + // the proper time. Alas, it cannot be communicated to Clang's thread-safety + // checker that such a guard is associated with `mMutex`. + // + void Replace(Data&& aData) MOZ_CAPABILITY_RELEASE(mMutex) { + // either both handles are NULL, or neither is + MOZ_ASSERT(!!aData.handle == !!aData.waitHandle); + + if (mData.handle) { + MOZ_LOG(sHWLog, LogLevel::Info, + ("Stop callback: HW %p | handle %p | target %p | PTP_WAIT %p", + this, mData.handle, mData.target.get(), mData.waitHandle.get())); + } + + if (mData.target) { + mData.target->UnregisterShutdownTask(this); + } + + // Extract the old data and insert the new -- but hold onto the old data for + // now. (See [1] and [2], below.) + Data oldData = std::exchange(mData, std::move(aData)); + + //////////////////////////////////////////////////////////////////////////// + // Release the mutex. + mMutex.Unlock(); + //////////////////////////////////////////////////////////////////////////// + + // [1] `oldData.self` will be unset if the old callback already ran (or if + // there was no old callback in the first place). If it's set, though, we + // need to explicitly clear out the wait-object first. + if (oldData.self) { + MOZ_ASSERT(oldData.waitHandle); + FlushWaitHandle(oldData.waitHandle.get()); + } + + // [2] oldData also includes several other reference-counted pointers. It's + // possible that these may be the last pointer to something, so releasing + // them may have arbitrary side-effects -- like calling this->Stop(), which + // will try to reacquire the mutex. + // + // Now that we've released the mutex, we can (implicitly) release them all + // here. + } + + // Either confirm as complete or cancel any callbacks on aWaitHandle. Block + // until this is done. (See documentation for ::CloseThreadpoolWait().) + void FlushWaitHandle(PTP_WAIT aWaitHandle) MOZ_EXCLUDES(mMutex) { + ::SetThreadpoolWait(aWaitHandle, nullptr, nullptr); + // This might block on `OnWaitCompleted()`, so we can't hold `mMutex` here. + ::WaitForThreadpoolWaitCallbacks(aWaitHandle, TRUE); + // ::CloseThreadpoolWait() itself is the caller's responsibility. + } +}; + +NS_IMPL_ISUPPORTS(HandleWatcher::Impl, nsITargetShutdownTask) + +////// +// HandleWatcher member function implementations + +HandleWatcher::HandleWatcher() : mImpl{} {} +HandleWatcher::~HandleWatcher() { + if (mImpl) { + MOZ_ASSERT(mImpl->IsStopped()); + mImpl->Stop(); // just in case, in release + } +} + +HandleWatcher::HandleWatcher(HandleWatcher&&) noexcept = default; +HandleWatcher& HandleWatcher::operator=(HandleWatcher&&) noexcept = default; + +void HandleWatcher::Watch(HANDLE aHandle, nsIEventTarget* aTarget, + already_AddRefed aRunnable) { + auto impl = Impl::Create(aHandle, aTarget, std::move(aRunnable)); + MOZ_ASSERT(impl); + + if (mImpl) { + mImpl->Stop(); + } + mImpl = std::move(impl); +} + +void HandleWatcher::Stop() { + if (mImpl) { + mImpl->Stop(); + } +} + +bool HandleWatcher::IsStopped() { return !mImpl || mImpl->IsStopped(); } + +} // namespace mozilla -- cgit v1.2.3