libreoffice/svl/source/notify/broadcast.cxx

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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 * 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
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 *   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
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#include <svl/broadcast.hxx>
#include <svl/listener.hxx>
#include <svl/hint.hxx>
#include <o3tl/safeint.hxx>
#include <cassert>
#include <algorithm>

/**
 Design Notes
 -------------------------------

 This class is extremely heavily used - we can have millions of broadcasters and listeners and we can also
 have a broadcaster that has a million listeners.

 So we do a number of things
 (*) use a cache-dense listener list (std::vector) because caching effects dominate a lot of operations
 (*) use a sorted list to speed up find operations
 (*) only sort the list when we absolutely have to, to speed up sequential add/remove operations
 (*) defer removing items from the list by (ab)using the last bit of the pointer

 Also we have some complications around destruction because
 (*) we broadcast a message to indicate that we are destructing
 (*) which can trigger arbitrality complicated behaviour, including
 (*) adding a removing things from the in-destruction object!

*/

static bool isDeletedPtr(SvtListener* p)
{
    /** mark deleted entries by toggling the last bit,which is effectively unused, since the struct we point
     * to is at least 16-bit aligned. This allows the binary search to continue working even when we have
     * deleted entries */
    return (reinterpret_cast<uintptr_t>(p) & 0x01) == 0x01;
}

static void markDeletedPtr(SvtListener*& rp)
{
    reinterpret_cast<uintptr_t&>(rp) |= 0x01;
}

static void sortListeners(std::vector<SvtListener*>& listeners, size_t firstUnsorted)
{
    // Add() only appends new values, so often the container will be sorted expect for one
    // or few last items. For larger containers it is much more efficient to just handle
    // the unsorted part.
    auto sortedEnd = firstUnsorted == 0
        ? std::is_sorted_until(listeners.begin(),listeners.end())
        : listeners.begin() + firstUnsorted;
    if( listeners.end() - sortedEnd == 1 )
    {   // Just one item, insert it in the right place.
        SvtListener* item = listeners.back();
        listeners.pop_back();
        listeners.insert( std::upper_bound( listeners.begin(), listeners.end(), item ), item );
    }
    else if( o3tl::make_unsigned( sortedEnd - listeners.begin()) > listeners.size() * 3 / 4 )
    {   // Sort the unsorted part and then merge.
        std::sort( sortedEnd, listeners.end());
        std::inplace_merge( listeners.begin(), sortedEnd, listeners.end());
    }
    else
    {
        std::sort(listeners.begin(), listeners.end());
    }
}

void SvtBroadcaster::Normalize() const
{
    // clear empty slots first, because then we often have to do very little sorting
    if (mnEmptySlots)
    {
        std::erase_if(maListeners, [] (SvtListener* p) { return isDeletedPtr(p); });
        mnEmptySlots = 0;
    }

    if (mnListenersFirstUnsorted != static_cast<sal_Int32>(maListeners.size()))
    {
        sortListeners(maListeners, mnListenersFirstUnsorted);
        mnListenersFirstUnsorted = maListeners.size();
    }

    if (!mbDestNormalized)
    {
        sortListeners(maDestructedListeners, 0);
        mbDestNormalized = true;
    }
}

void SvtBroadcaster::Add( SvtListener* p )
{
    assert(!mbDisposing && "called inside my own destructor?");
    assert(!mbAboutToDie && "called after PrepareForDestruction()?");
    if (mbDisposing || mbAboutToDie)
        return;
    // Avoid normalizing if the item appended keeps the container sorted.
    auto nRealSize = static_cast<sal_Int32>(maListeners.size() - mnEmptySlots);
    auto bSorted = mnListenersFirstUnsorted == nRealSize;
    if (maListeners.empty() || (bSorted && maListeners.back() <= p))
    {
        ++mnListenersFirstUnsorted;
        maListeners.push_back(p);
        return;
    }
    // see if we can stuff it into an empty slot, which succeeds surprisingly often in
    // some calc workloads where it removes and then re-adds the same listener
    if (mnEmptySlots && bSorted)
    {
        auto it = std::lower_bound(maListeners.begin(), maListeners.end(), p);
        if (it != maListeners.end() && isDeletedPtr(*it))
        {
            *it = p;
            ++mnListenersFirstUnsorted;
            --mnEmptySlots;
            return;
        }
    }
    maListeners.push_back(p);
}

void SvtBroadcaster::Remove( SvtListener* p )
{
    if (mbDisposing)
        return;

    if (mbAboutToDie)
    {
        // only reset mbDestNormalized if we are going to become unsorted
        if (!maDestructedListeners.empty() && maDestructedListeners.back() > p)
            mbDestNormalized = false;
        maDestructedListeners.push_back(p);
        return;
    }

    // We only need to fully normalize if one or more Add()s have been performed that make the array unsorted.
    auto nRealSize = static_cast<sal_Int32>(maListeners.size() - mnEmptySlots);
    if (mnListenersFirstUnsorted != nRealSize || (maListeners.size() > 1024 && maListeners.size() / nRealSize > 16))
        Normalize();

    auto it = std::lower_bound(maListeners.begin(), maListeners.end(), p);
    assert (it != maListeners.end() && *it == p);
    if (it != maListeners.end() && *it == p)
    {
        markDeletedPtr(*it);
        ++mnEmptySlots;
        --mnListenersFirstUnsorted;
    }

    if (!HasListeners())
        ListenersGone();
}

SvtBroadcaster::SvtBroadcaster( const SvtBroadcaster &rBC ) :
    mnEmptySlots(0), mnListenersFirstUnsorted(0),
    mbAboutToDie(false), mbDisposing(false),
    mbDestNormalized(true)
{
    assert(!rBC.mbAboutToDie && "copying an object marked with PrepareForDestruction()?");
    assert(!rBC.mbDisposing && "copying an object that is in its destructor?");

    rBC.Normalize(); // so that insert into ourself is in-order, and therefore we do not need to Normalize()
    maListeners.reserve(rBC.maListeners.size());
    for (SvtListener* p : rBC.maListeners)
         p->StartListening(*this); // this will call back into this->Add()
}

SvtBroadcaster::~SvtBroadcaster()
{
    mbDisposing = true;
    Broadcast( SfxHint(SfxHintId::Dying) );

    Normalize();

    // now when both lists are sorted, we can linearly unregister all
    // listeners, with the exception of those that already asked to be removed
    // during their own destruction
    ListenersType::const_iterator dest(maDestructedListeners.begin());
    for (auto& rpListener : maListeners)
    {
        // skip the destructed ones
        while (dest != maDestructedListeners.end() && (*dest < rpListener))
            ++dest;

        if (dest == maDestructedListeners.end() || *dest != rpListener)
            rpListener->BroadcasterDying(*this);
    }
}

void SvtBroadcaster::Broadcast( const SfxHint &rHint )
{
    Normalize();

    ListenersType::const_iterator dest(maDestructedListeners.begin());
    ListenersType aListeners(maListeners); // this copy is important to avoid erasing entries while iterating
    for (auto& rpListener : aListeners)
    {
        // skip the destructed ones
        while (dest != maDestructedListeners.end() && (*dest < rpListener))
            ++dest;

        if (dest == maDestructedListeners.end() || *dest != rpListener)
            rpListener->Notify(rHint);
    }
}

void SvtBroadcaster::ListenersGone() {}

SvtBroadcaster::ListenersType& SvtBroadcaster::GetAllListeners()
{
    Normalize();
    return maListeners;
}

const SvtBroadcaster::ListenersType& SvtBroadcaster::GetAllListeners() const
{
    Normalize();
    return maListeners;
}

void SvtBroadcaster::PrepareForDestruction()
{
    mbAboutToDie = true;
    // the reserve() serves two purpose (1) performance (2) makes sure our iterators do not become invalid
    maDestructedListeners.reserve(maListeners.size());
}

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