98 lines
3.2 KiB
C++
98 lines
3.2 KiB
C++
#ifndef BASE_WIN_OBJECT_WATCHER_H_
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#define BASE_WIN_OBJECT_WATCHER_H_
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#pragma once
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#include "base/base_export.h"
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#include "base/base_config.h"
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#include "base/framework/message_loop.h"
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#include "base/callback/callback.h"
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namespace nbase {
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namespace win32 {
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// A class that provides a means to asynchronously wait for a Windows object to
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// become signaled. It is an abstraction around RegisterWaitForSingleObject
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// that provides a notification callback, OnObjectSignaled, that runs back on
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// the origin thread (i.e., the thread that called StartWatching).
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//
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// This class acts like a smart pointer such that when it goes out-of-scope,
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// UnregisterWaitEx is automatically called, and any in-flight notification is
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// suppressed.
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//
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// Typical usage:
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//
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// class MyClass : public base::ObjectWatcher::Delegate {
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// public:
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// void DoStuffWhenSignaled(HANDLE object) {
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// watcher_.StartWatching(object, this);
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// }
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// virtual void OnObjectSignaled(HANDLE object) {
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// // OK, time to do stuff!
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// }
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// private:
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// base::ObjectWatcher watcher_;
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// };
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//
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// In the above example, MyClass wants to "do stuff" when object becomes
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// signaled. ObjectWatcher makes this task easy. When MyClass goes out of
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// scope, the watcher_ will be destroyed, and there is no need to worry about
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// OnObjectSignaled being called on a deleted MyClass pointer. Easy!
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//
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class BASE_EXPORT ObjectWatcher : public nbase::SupportWeakCallback, public MessageLoop::DestructionObserver
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{
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public:
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class BASE_EXPORT Delegate {
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public:
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virtual ~Delegate() {}
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// Called from the MessageLoop when a signaled object is detected. To
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// continue watching the object, StartWatching must be called again.
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virtual void OnObjectSignaled(HANDLE object) = 0;
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};
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ObjectWatcher();
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~ObjectWatcher();
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// When the object is signaled, the given delegate is notified on the thread
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// where StartWatching is called. The ObjectWatcher is not responsible for
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// deleting the delegate.
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//
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// Returns true if the watch was started. Otherwise, false is returned.
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//
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bool StartWatching(HANDLE object, Delegate* delegate);
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// Stops watching. Does nothing if the watch has already completed. If the
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// watch is still active, then it is canceled, and the associated delegate is
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// not notified.
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//
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// Returns true if the watch was canceled. Otherwise, false is returned.
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//
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bool StopWatching();
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// Returns the handle of the object being watched, or NULL if the object
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// watcher is stopped.
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HANDLE GetWatchedObject();
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private:
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// Called on a background thread when done waiting.
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static void CALLBACK DoneWaiting(void* param, BOOLEAN timed_out);
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void Signal(Delegate* delegate);
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// MessageLoop::DestructionObserver implementation:
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virtual void PreDestroyCurrentMessageLoop();
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// Internal state.
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nbase::WeakCallbackFlag signal_weakflag_;
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StdClosure callback_;
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HANDLE object_; // The object being watched
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HANDLE wait_object_; // Returned by RegisterWaitForSingleObject
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MessageLoop* origin_loop_; // Used to get back to the origin thread
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DISALLOW_COPY_AND_ASSIGN(ObjectWatcher);
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};
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} // namespace win32
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} // namespace nbase
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#endif // BASE_OBJECT_WATCHER_H_
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