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/**
* @file llpacketring.cpp
* @brief implementation of LLPacketRing class.
*
* $LicenseInfo:firstyear=2001&license=viewerlgpl$
* Second Life Viewer Source Code
* Copyright (C) 2010, Linden Research, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation;
* version 2.1 of the License only.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Linden Research, Inc., 945 Battery Street, San Francisco, CA 94111 USA
* $/LicenseInfo$
*/
#include "linden_common.h"
#include "llpacketring.h"
#include "llerror.h"
constexpr S16 MAX_BUFFER_RING_SIZE = 8192;
// DANGER: don't adjust DEFAULT_BUFFER_RING_SIZE unless you know what
// you're doing. Its value affects the "buffer load rate" which is used
// to supply backpressure to an overloaded nework queue.
constexpr S16 DEFAULT_BUFFER_RING_SIZE = 256;
LLPacketRing::LLPacketRing()
: mRing(DEFAULT_BUFFER_RING_SIZE, nullptr)
{
LLHost invalid_host;
for (size_t i = 0; i < mRing.size(); ++i)
{
mRing[i] = new LLPacketBuffer(invalid_host, nullptr, 0);
}
}
LLPacketRing::~LLPacketRing()
{
for (auto* packet : mRing)
{
delete packet;
}
mRing.clear();
mNumBufferedPackets = 0;
mNumBufferedBytes = 0;
mHeadIndex = 0;
}
void LLPacketRing::pushPacket(const LLPacketBuffer& packet)
{
S16 ring_size = (S16)mRing.size();
if (mNumBufferedPackets >= ring_size && ring_size < MAX_BUFFER_RING_SIZE)
{
expandRing();
ring_size = (S16)mRing.size();
}
LLPacketBuffer* slot = mRing[mHeadIndex];
S32 old_size = slot->getSize();
*slot = packet;
mHeadIndex = (mHeadIndex + 1) % ring_size;
if (mNumBufferedPackets < ring_size)
{
++mNumBufferedPackets;
mNumBufferedBytes += packet.getSize();
}
else
{
// Ring is at maximum capacity; oldest packet was overwritten.
// This is VERY BAD because we've already ACKed the packet we're loosing
// (if it was "reliable").
LL_WARNS("PacketRing") << "buffer overflow at " << mNumBufferedPackets << " packets" << LL_ENDL;
mNumBufferedBytes += packet.getSize() - old_size;
}
}
bool LLPacketRing::popPacket(LLPacketBuffer& packet)
{
if (mNumBufferedPackets <= 0)
{
return false;
}
S16 ring_size = (S16)mRing.size();
S16 tail_index = (mHeadIndex + ring_size - mNumBufferedPackets) % ring_size;
LLPacketBuffer* slot = mRing[tail_index];
S32 packet_size = slot->getSize();
packet = *slot;
--mNumBufferedPackets;
mNumBufferedBytes -= packet_size;
llassert(mNumBufferedPackets > 0 || mNumBufferedBytes == 0);
return true;
}
bool LLPacketRing::expandRing()
{
constexpr S16 BUFFER_RING_EXPANSION = 512;
S16 old_size = (S16)mRing.size();
S16 new_size = llmin(old_size + BUFFER_RING_EXPANSION, MAX_BUFFER_RING_SIZE);
if (new_size == old_size)
{
return false;
}
// Lay existing entries out linearly in FIFO order starting at index 0.
std::vector<LLPacketBuffer*> new_ring(new_size, nullptr);
for (S16 i = 0; i < old_size; ++i)
{
S16 j = (mHeadIndex + i) % old_size;
new_ring[i] = mRing[j];
}
LLHost invalid_host;
for (S16 i = old_size; i < new_size; ++i)
{
new_ring[i] = new LLPacketBuffer(invalid_host, nullptr, 0);
}
mRing.swap(new_ring);
mHeadIndex = mNumBufferedPackets;
return true;
}
F32 LLPacketRing::getBufferLoadRate() const
{
return (F32)mNumBufferedPackets / (F32)DEFAULT_BUFFER_RING_SIZE;
}
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