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diff --git a/include/VBox/com/EventQueue.h b/include/VBox/com/EventQueue.h
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+/* $Id: EventQueue.h $ */
+/** @file
+ * MS COM / XPCOM Abstraction Layer - Event queue class declaration.
+ */
+
+/*
+ * Copyright (C) 2013-2020 Oracle Corporation
+ *
+ * This file is part of VirtualBox Open Source Edition (OSE), as
+ * available from http://www.virtualbox.org. This file is free software;
+ * you can redistribute it and/or modify it under the terms of the GNU
+ * General Public License (GPL) as published by the Free Software
+ * Foundation, in version 2 as it comes in the "COPYING" file of the
+ * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
+ * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
+ *
+ * The contents of this file may alternatively be used under the terms
+ * of the Common Development and Distribution License Version 1.0
+ * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
+ * VirtualBox OSE distribution, in which case the provisions of the
+ * CDDL are applicable instead of those of the GPL.
+ *
+ * You may elect to license modified versions of this file under the
+ * terms and conditions of either the GPL or the CDDL or both.
+ */
+
+#ifndef VBOX_INCLUDED_com_EventQueue_h
+#define VBOX_INCLUDED_com_EventQueue_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#include <list>
+
+#include <iprt/asm.h>
+#include <iprt/critsect.h>
+
+#include <VBox/com/defs.h>
+#include <VBox/com/assert.h>
+
+
+/** @defgroup grp_com_evtqueue  Event Queue Classes
+ * @ingroup grp_com
+ * @{
+ */
+
+namespace com
+{
+
+class EventQueue;
+
+/**
+ *  Base class for all events. Intended to be subclassed to introduce new
+ *  events and handlers for them.
+ *
+ *  Subclasses usually reimplement virtual #handler() (that does nothing by
+ *  default) and add new data members describing the event.
+ */
+class Event
+{
+public:
+
+    Event(void) :
+        mRefCount(0) { }
+    virtual ~Event(void) { AssertMsg(!mRefCount,
+                                     ("Reference count of event=%p not 0 on destruction (is %RU32)\n",
+                                      this, mRefCount)); }
+public:
+
+    uint32_t AddRef(void) { return ASMAtomicIncU32(&mRefCount); }
+    void     Release(void)
+    {
+        Assert(mRefCount);
+        uint32_t cRefs = ASMAtomicDecU32(&mRefCount);
+        if (!cRefs)
+            delete this;
+    }
+
+protected:
+
+    /**
+     *  Event handler. Called in the context of the event queue's thread.
+     *  Always reimplemented by subclasses
+     *
+     *  @return reserved, should be NULL.
+     */
+    virtual void *handler(void) { return NULL; }
+
+    friend class EventQueue;
+
+protected:
+
+    /** The event's reference count. */
+    uint32_t mRefCount;
+};
+
+typedef std::list< Event* >                 EventQueueList;
+typedef std::list< Event* >::iterator       EventQueueListIterator;
+typedef std::list< Event* >::const_iterator EventQueueListIteratorConst;
+
+/**
+ *  Simple event queue.
+ */
+class EventQueue
+{
+public:
+
+    EventQueue(void);
+    virtual ~EventQueue(void);
+
+public:
+
+    BOOL postEvent(Event *event);
+    int processEventQueue(RTMSINTERVAL cMsTimeout);
+    int processPendingEvents(size_t cNumEvents);
+    int interruptEventQueueProcessing();
+
+private:
+
+    /** Critical section for serializing access to this
+     *  event queue. */
+    RTCRITSECT         mCritSect;
+    /** Number of concurrent users. At the moment we
+     *  only support one concurrent user at a time when
+        calling processEventQueue(). */
+    uint32_t           mUserCnt;
+    /** Event semaphore for getting notified on new
+     *  events being handled. */
+    RTSEMEVENT         mSemEvent;
+    /** The actual event queue, implemented as a list. */
+    EventQueueList     mEvents;
+    /** Shutdown indicator. */
+    bool               mShutdown;
+};
+
+} /* namespace com */
+
+/** @} */
+
+#endif /* !VBOX_INCLUDED_com_EventQueue_h */
+