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diff --git a/comphelper/source/misc/accessibleeventnotifier.cxx b/comphelper/source/misc/accessibleeventnotifier.cxx
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+++ b/comphelper/source/misc/accessibleeventnotifier.cxx
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * 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/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ *   Licensed to the Apache Software Foundation (ASF) under one or more
+ *   contributor license agreements. See the NOTICE file distributed
+ *   with this work for additional information regarding copyright
+ *   ownership. The ASF licenses this file to you under the Apache
+ *   License, Version 2.0 (the "License"); you may not use this file
+ *   except in compliance with the License. You may obtain a copy of
+ *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
+ */
+
+#include <comphelper/accessibleeventnotifier.hxx>
+#include <com/sun/star/accessibility/XAccessibleEventListener.hpp>
+#include <comphelper/interfacecontainer4.hxx>
+
+#include <map>
+#include <memory>
+#include <limits>
+
+using namespace ::com::sun::star::uno;
+using namespace ::com::sun::star::lang;
+using namespace ::com::sun::star::accessibility;
+using namespace ::comphelper;
+
+namespace {
+
+typedef std::pair< AccessibleEventNotifier::TClientId,
+        AccessibleEventObject > ClientEvent;
+
+typedef ::comphelper::OInterfaceContainerHelper4<XAccessibleEventListener> ListenerContainer;
+typedef std::map< AccessibleEventNotifier::TClientId, ListenerContainer* > ClientMap;
+
+/// key is the end of the interval, value is the start of the interval
+typedef std::map<AccessibleEventNotifier::TClientId,
+            AccessibleEventNotifier::TClientId> IntervalMap;
+
+std::mutex& GetLocalMutex()
+{
+    static std::mutex MUTEX;
+    return MUTEX;
+}
+
+ClientMap gaClients;
+
+IntervalMap& GetFreeIntervals()
+{
+    static IntervalMap MAP =
+    []()
+    {
+        IntervalMap map;
+        map.insert(std::make_pair(
+            std::numeric_limits<AccessibleEventNotifier::TClientId>::max(), 1));
+        return map;
+    }();
+    return MAP;
+}
+
+void releaseId(AccessibleEventNotifier::TClientId const nId)
+{
+    IntervalMap & rFreeIntervals(GetFreeIntervals());
+    IntervalMap::iterator const upper(rFreeIntervals.upper_bound(nId));
+    assert(upper != rFreeIntervals.end());
+    assert(nId < upper->second); // second is start of the interval!
+    if (nId + 1 == upper->second)
+    {
+        --upper->second; // add nId to existing interval
+    }
+    else
+    {
+        IntervalMap::iterator const lower(rFreeIntervals.lower_bound(nId));
+        if (lower != rFreeIntervals.end() && lower->first == nId - 1)
+        {
+            // add nId by replacing lower with new merged entry
+            rFreeIntervals.insert(std::make_pair(nId, lower->second));
+            rFreeIntervals.erase(lower);
+        }
+        else // otherwise just add new 1-element interval
+        {
+            rFreeIntervals.insert(std::make_pair(nId, nId));
+        }
+    }
+    // currently it's not checked whether intervals can be merged now
+    // hopefully that won't be a problem in practice
+}
+
+/// generates a new client id
+AccessibleEventNotifier::TClientId generateId()
+{
+    IntervalMap & rFreeIntervals(GetFreeIntervals());
+    assert(!rFreeIntervals.empty());
+    IntervalMap::iterator const iter(rFreeIntervals.begin());
+    AccessibleEventNotifier::TClientId const nFirst = iter->first;
+    AccessibleEventNotifier::TClientId const nFreeId = iter->second;
+    assert(nFreeId <= nFirst);
+    if (nFreeId != nFirst)
+    {
+        ++iter->second; // remove nFreeId from interval
+    }
+    else
+    {
+        rFreeIntervals.erase(iter); // remove 1-element interval
+    }
+
+    assert(gaClients.end() == gaClients.find(nFreeId));
+
+    return nFreeId;
+}
+
+/** looks up a client in our client map, asserts if it cannot find it or
+    no event thread is present
+
+    @precond
+        to be called with our mutex locked
+
+    @param nClient
+        the id of the client to lookup
+    @param rPos
+        out-parameter for the position of the client in the client map
+
+    @return
+        <TRUE/> if and only if the client could be found and
+        <arg>rPos</arg> has been filled with its position
+*/
+bool implLookupClient(
+        const AccessibleEventNotifier::TClientId nClient,
+        ClientMap::iterator& rPos )
+{
+    // look up this client
+    ClientMap &rClients = gaClients;
+    rPos = rClients.find( nClient );
+    assert( rClients.end() != rPos &&
+        "AccessibleEventNotifier::implLookupClient: invalid client id "
+        "(did you register your client?)!" );
+
+    return ( rClients.end() != rPos );
+}
+
+} // anonymous namespace
+
+namespace comphelper {
+
+AccessibleEventNotifier::TClientId AccessibleEventNotifier::registerClient()
+{
+    std::scoped_lock aGuard( GetLocalMutex() );
+
+    // generate a new client id
+    TClientId nNewClientId = generateId( );
+
+    // the event listeners for the new client
+    ListenerContainer * pNewListeners = new ListenerContainer();
+    // add the client
+    gaClients.emplace( nNewClientId, pNewListeners );
+
+    // outta here
+    return nNewClientId;
+}
+
+void AccessibleEventNotifier::revokeClient( const TClientId _nClient )
+{
+    std::scoped_lock aGuard( GetLocalMutex() );
+
+    ClientMap::iterator aClientPos;
+    if ( !implLookupClient( _nClient, aClientPos ) )
+        // already asserted in implLookupClient
+        return;
+
+    // remove it from the clients map
+    delete aClientPos->second;
+    gaClients.erase( aClientPos );
+    releaseId(_nClient);
+}
+
+void AccessibleEventNotifier::revokeClientNotifyDisposing(
+    const TClientId _nClient, const Reference< XInterface >& _rxEventSource )
+{
+    std::unique_lock aGuard( GetLocalMutex() );
+
+    ClientMap::iterator aClientPos;
+    if (!implLookupClient(_nClient, aClientPos))
+        // already asserted in implLookupClient
+        return;
+
+    // notify the listeners
+    std::unique_ptr<ListenerContainer> pListeners(aClientPos->second);
+
+    // we do not need the entry in the clients map anymore
+    // (do this before actually notifying, because some client
+    // implementations have re-entrance problems and call into
+    // revokeClient while we are notifying from here)
+    gaClients.erase(aClientPos);
+    releaseId(_nClient);
+
+    // notify the "disposing" event for this client
+    EventObject aDisposalEvent;
+    aDisposalEvent.Source = _rxEventSource;
+
+    // now really do the notification
+    pListeners->disposeAndClear( aGuard, aDisposalEvent );
+}
+
+sal_Int32 AccessibleEventNotifier::addEventListener(
+    const TClientId _nClient, const Reference< XAccessibleEventListener >& _rxListener )
+{
+    std::unique_lock aGuard( GetLocalMutex() );
+
+    ClientMap::iterator aClientPos;
+    if ( !implLookupClient( _nClient, aClientPos ) )
+        // already asserted in implLookupClient
+        return 0;
+
+    if ( _rxListener.is() )
+        aClientPos->second->addInterface( aGuard, _rxListener );
+
+    return aClientPos->second->getLength(aGuard);
+}
+
+sal_Int32 AccessibleEventNotifier::removeEventListener(
+    const TClientId _nClient, const Reference< XAccessibleEventListener >& _rxListener )
+{
+    std::unique_lock aGuard( GetLocalMutex() );
+
+    ClientMap::iterator aClientPos;
+    if ( !implLookupClient( _nClient, aClientPos ) )
+        // already asserted in implLookupClient
+        return 0;
+
+    if ( _rxListener.is() )
+        aClientPos->second->removeInterface( aGuard,  _rxListener );
+
+    return aClientPos->second->getLength(aGuard);
+}
+
+void AccessibleEventNotifier::addEvent( const TClientId _nClient, const AccessibleEventObject& _rEvent )
+{
+    std::vector< Reference< XAccessibleEventListener > > aListeners;
+
+    {
+        std::unique_lock aGuard( GetLocalMutex() );
+
+        ClientMap::iterator aClientPos;
+        if ( !implLookupClient( _nClient, aClientPos ) )
+            // already asserted in implLookupClient
+            return;
+
+        // since we're synchronous, again, we want to notify immediately
+        aListeners = aClientPos->second->getElements(aGuard);
+    }
+
+    // default handling: loop through all listeners, and notify them
+    for ( const auto& rListener : aListeners )
+    {
+        try
+        {
+            rListener->notifyEvent( _rEvent );
+        }
+        catch( const Exception& )
+        {
+            // no assertion, because a broken access remote bridge or something like this
+            // can cause this exception
+        }
+    }
+}
+
+} // namespace comphelper
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */