The Tor Browser: comparison ipc/chromium/src/base/waitable

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+:fc57ca3f1c01
+// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+#ifndef BASE_WAITABLE_EVENT_H_
+#define BASE_WAITABLE_EVENT_H_
+#include "base/basictypes.h"
+#if defined(OS_WIN)
+#include <windows.h>
+#endif
+#if defined(OS_POSIX)
+#include <list>
+#include <utility>
+#include "base/condition_variable.h"
+#include "base/lock.h"
+#include "base/ref_counted.h"
+#endif
+#include "base/message_loop.h"
+namespace base {
+// This replaces INFINITE from Win32
+static const int kNoTimeout = -1;
+class TimeDelta;
+// A WaitableEvent can be a useful thread synchronization tool when you want to
+// allow one thread to wait for another thread to finish some work. For
+// non-Windows systems, this can only be used from within a single address
+// space.
+//
+// Use a WaitableEvent when you would otherwise use a Lock+ConditionVariable to
+// protect a simple boolean value.  However, if you find yourself using a
+// WaitableEvent in conjunction with a Lock to wait for a more complex state
+// change (e.g., for an item to be added to a queue), then you should probably
+// be using a ConditionVariable instead of a WaitableEvent.
+//
+// NOTE: On Windows, this class provides a subset of the functionality afforded
+// by a Windows event object.  This is intentional.  If you are writing Windows
+// specific code and you need other features of a Windows event, then you might
+// be better off just using an Windows event directly.
+class WaitableEvent {
+public:
+// If manual_reset is true, then to set the event state to non-signaled, a
+// consumer must call the Reset method.  If this parameter is false, then the
+// system automatically resets the event state to non-signaled after a single
+// waiting thread has been released.
+WaitableEvent(bool manual_reset, bool initially_signaled);
+#if defined(OS_WIN)
+// Create a WaitableEvent from an Event HANDLE which has already been
+// created. This objects takes ownership of the HANDLE and will close it when
+// deleted.
+explicit WaitableEvent(HANDLE event_handle);
+// Releases ownership of the handle from this object.
+HANDLE Release();
+#endif
+~WaitableEvent();
+// Put the event in the un-signaled state.
+void Reset();
+// Put the event in the signaled state.  Causing any thread blocked on Wait
+// to be woken up.
+void Signal();
+// Returns true if the event is in the signaled state, else false.  If this
+// is not a manual reset event, then this test will cause a reset.
+bool IsSignaled();
+// Wait indefinitely for the event to be signaled.  Returns true if the event
+// was signaled, else false is returned to indicate that waiting failed.
+bool Wait();
+// Wait up until max_time has passed for the event to be signaled.  Returns
+// true if the event was signaled.  If this method returns false, then it
+// does not necessarily mean that max_time was exceeded.
+bool TimedWait(const TimeDelta& max_time);
+#if defined(OS_WIN)
+HANDLE handle() const { return handle_; }
+#endif
+// Wait, synchronously, on multiple events.
+//   waitables: an array of WaitableEvent pointers
+//   count: the number of elements in @waitables
+//
+// returns: the index of a WaitableEvent which has been signaled.
+//
+// You MUST NOT delete any of the WaitableEvent objects while this wait is
+// happening.
+static size_t WaitMany(WaitableEvent** waitables, size_t count);
+// For asynchronous waiting, see WaitableEventWatcher
+// This is a private helper class. It's here because it's used by friends of
+// this class (such as WaitableEventWatcher) to be able to enqueue elements
+// of the wait-list
+class Waiter {
+public:
+// Signal the waiter to wake up.
+//
+// Consider the case of a Waiter which is in multiple WaitableEvent's
+// wait-lists. Each WaitableEvent is automatic-reset and two of them are
+// signaled at the same time. Now, each will wake only the first waiter in
+// the wake-list before resetting. However, if those two waiters happen to
+// be the same object (as can happen if another thread didn't have a chance
+// to dequeue the waiter from the other wait-list in time), two auto-resets
+// will have happened, but only one waiter has been signaled!
+//
+// Because of this, a Waiter may "reject" a wake by returning false. In
+// this case, the auto-reset WaitableEvent shouldn't act as if anything has
+// been notified.
+virtual bool Fire(WaitableEvent* signaling_event) = 0;
+// Waiters may implement this in order to provide an extra condition for
+// two Waiters to be considered equal. In WaitableEvent::Dequeue, if the
+// pointers match then this function is called as a final check. See the
+// comments in ~Handle for why.
+virtual bool Compare(void* tag) = 0;
+};
+private:
+friend class WaitableEventWatcher;
+#if defined(OS_WIN)
+HANDLE handle_;
+#else
+// On Windows, one can close a HANDLE which is currently being waited on. The
+// MSDN documentation says that the resulting behaviour is 'undefined', but
+// it doesn't crash. However, if we were to include the following members
+// directly then, on POSIX, one couldn't use WaitableEventWatcher to watch an
+// event which gets deleted. This mismatch has bitten us several times now,
+// so we have a kernel of the WaitableEvent, which is reference counted.
+// WaitableEventWatchers may then take a reference and thus match the Windows
+// behaviour.
+struct WaitableEventKernel :
+public RefCountedThreadSafe<WaitableEventKernel> {
+public:
+WaitableEventKernel(bool manual_reset, bool initially_signaled)
+: manual_reset_(manual_reset),
+signaled_(initially_signaled) {
+}
+bool Dequeue(Waiter* waiter, void* tag);
+Lock lock_;
+const bool manual_reset_;
+bool signaled_;
+std::list<Waiter*> waiters_;
+};
+scoped_refptr<WaitableEventKernel> kernel_;
+bool SignalAll();
+bool SignalOne();
+void Enqueue(Waiter* waiter);
+// When dealing with arrays of WaitableEvent*, we want to sort by the address
+// of the WaitableEvent in order to have a globally consistent locking order.
+// In that case we keep them, in sorted order, in an array of pairs where the
+// second element is the index of the WaitableEvent in the original,
+// unsorted, array.
+typedef std::pair<WaitableEvent*, size_t> WaiterAndIndex;
+static size_t EnqueueMany(WaiterAndIndex* waitables,
+size_t count, Waiter* waiter);
+#endif
+DISALLOW_COPY_AND_ASSIGN(WaitableEvent);
+};
+}  // namespace base
+#endif  // BASE_WAITABLE_EVENT_H_

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comparison: ipc/chromium/src/base/waitable_event.h

ipc/chromium/src/base/waitable_event.h