summaryrefslogtreecommitdiff
path: root/base/synchronization/waitable_event.h
diff options
context:
space:
mode:
Diffstat (limited to 'base/synchronization/waitable_event.h')
-rw-r--r--base/synchronization/waitable_event.h181
1 files changed, 181 insertions, 0 deletions
diff --git a/base/synchronization/waitable_event.h b/base/synchronization/waitable_event.h
new file mode 100644
index 0000000..62712ed
--- /dev/null
+++ b/base/synchronization/waitable_event.h
@@ -0,0 +1,181 @@
+// Copyright (c) 2011 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_SYNCHRONIZATION_WAITABLE_EVENT_H_
+#define BASE_SYNCHRONIZATION_WAITABLE_EVENT_H_
+#pragma once
+
+#include "base/base_export.h"
+#include "base/basictypes.h"
+
+#if defined(OS_WIN)
+#include <windows.h>
+#endif
+
+#if defined(OS_POSIX)
+#include <list>
+#include <utility>
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#endif
+
+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 BASE_EXPORT 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;
+
+ protected:
+ virtual ~Waiter() {}
+ };
+
+ 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);
+ virtual ~WaitableEventKernel();
+
+ bool Dequeue(Waiter* waiter, void* tag);
+
+ base::Lock lock_;
+ const bool manual_reset_;
+ bool signaled_;
+ std::list<Waiter*> waiters_;
+ };
+
+ typedef std::pair<WaitableEvent*, size_t> WaiterAndIndex;
+
+ // 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.
+ static size_t EnqueueMany(WaiterAndIndex* waitables,
+ size_t count, Waiter* waiter);
+
+ bool SignalAll();
+ bool SignalOne();
+ void Enqueue(Waiter* waiter);
+
+ scoped_refptr<WaitableEventKernel> kernel_;
+#endif
+
+ DISALLOW_COPY_AND_ASSIGN(WaitableEvent);
+};
+
+} // namespace base
+
+#endif // BASE_SYNCHRONIZATION_WAITABLE_EVENT_H_