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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 00:47:55 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 00:47:55 +0000 |
| commit | 26a029d407be480d791972afb5975cf62c9360a6 (patch) | |
| tree | f435a8308119effd964b339f76abb83a57c29483 /xpcom/threads/WinHandleWatcher.h | |
| parent | Initial commit. (diff) | |
| download | firefox-26a029d407be480d791972afb5975cf62c9360a6.tar.xz firefox-26a029d407be480d791972afb5975cf62c9360a6.zip | |
Adding upstream version 124.0.1.upstream/124.0.1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'xpcom/threads/WinHandleWatcher.h')
| -rw-r--r-- | xpcom/threads/WinHandleWatcher.h | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/xpcom/threads/WinHandleWatcher.h b/xpcom/threads/WinHandleWatcher.h new file mode 100644 index 0000000000..eb1e1c0245 --- /dev/null +++ b/xpcom/threads/WinHandleWatcher.h @@ -0,0 +1,117 @@ +/* -*- 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 WinHandleWatcher_h__ +#define WinHandleWatcher_h__ + +#include <minwindef.h> + +#include "mozilla/AlreadyAddRefed.h" +#include "mozilla/RefPtr.h" +#include "mozilla/UniquePtr.h" + +#include "nsIEventTarget.h" +#include "nsIRunnable.h" +#include "nsIThread.h" +#include "nsThreadUtils.h" + +namespace mozilla { +/////////////////////////////////////////////////////////////////////// +// HandleWatcher +// +// Enqueues a task onto an event target when a watched Win32 synchronization +// object [1] enters the signaled state. +// +// The HandleWatcher must be stopped before either it or the synchronization +// object is destroyed. +// +////// +// +// Example of use: +// +// ``` +// class MyClass { +// /* ... */ +// +// HANDLE CreateThing(); +// void OnComplete(); +// public: +// void Fire() { +// mHandle.set(CreateThing()); +// mWatcher.Watch( +// mHandle.get(), NS_GetCurrentThread(), // (or any other thread) +// NS_NewRunnableFunction("OnComplete", [this] { OnComplete(); })); +// } +// +// ~MyClass() { mWatcher.Stop(); } +// +// HandleWatcher mWatcher; +// HandlePtr mHandle; // calls ::CloseHandle() on destruction +// }; +// ``` +// +// Note: this example demonstrates why an explicit `Stop()` is necessary in +// MyClass's destructor. Without it, the `HandlePtr` would destroy the HANDLE -- +// and possibly whatever other data `OnComplete()` depends on -- before the +// watch was stopped! +// +// Rather than make code correctness silently dependent on member object order, +// we require that HandleWatcher already be stopped at its destruction time. +// (This does not guarantee correctness, as the task may still reference a +// partially-destroyed transitive owner; but, short of RIIR, a guarantee of +// correctness is probably not possible here.) +// +////// +// +// [1]https://learn.microsoft.com/en-us/windows/win32/sync/synchronization-objects +class HandleWatcher { + public: + class Impl; + + HandleWatcher(); + ~HandleWatcher(); + + HandleWatcher(HandleWatcher const&) = delete; + HandleWatcher& operator=(HandleWatcher const&) = delete; + + HandleWatcher(HandleWatcher&&) noexcept; + HandleWatcher& operator=(HandleWatcher&&) noexcept; + + // Watches the given Win32 HANDLE, which must be a synchronization object. As + // soon as the HANDLE is signaled, posts `aRunnable` to `aTarget`. + // + // `aHandle` is merely borrowed for the duration of the watch: the + // HandleWatcher does not attempt to close it, and its lifetime must exceed + // that of the watch. + // + // If the watch is stopped for any reason other than completion, `aRunnable` + // is released immediately, on the same thread from which the Watch was + // stopped. + // + // The watch is stopped when any of the following occurs: + // * `Stop()` is called. + // * `Watch()` is called again, even without an intervening `Stop()`. + // * This object is destroyed. + // * `aTarget` shuts down. + // * `aHandle` becomes signaled. + // + void Watch(HANDLE aHandle, nsIEventTarget* aTarget, + already_AddRefed<nsIRunnable> aRunnable); + + // Cancels the current watch, if any. + // + // Idempotent. Thread-safe with respect to other calls of `Stop()`. + void Stop(); + + // Potentially racy. Only intended for tests. + bool IsStopped(); + + private: + RefPtr<Impl> mImpl; +}; +} // namespace mozilla + +#endif // WinHandleWatcher_h__ |