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Minor improvement to multicast propagation algorithm.

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This commit is contained in:
Adam Ierymenko 2013-07-12 22:54:39 -04:00
parent aa59c1de10
commit c6dd5b239f
2 changed files with 24 additions and 28 deletions
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43
node/Multicaster.hpp
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@ -52,7 +52,7 @@
#include "Identity.hpp"
// Maximum sample size to pick during choice of multicast propagation peers
#define ZT_MULTICAST_PICK_MAX_SAMPLE_SIZE 32
#define ZT_MULTICAST_PICK_MAX_SAMPLE_SIZE (ZT_MULTICAST_PROPAGATION_BREADTH * 8)
namespace ZeroTier {
@ -224,6 +224,16 @@ public:
P toConsider[ZT_MULTICAST_PICK_MAX_SAMPLE_SIZE];
unsigned int sampleSize = 0;
// Decay a few random bits in bloom filter to probabilistically eliminate
// false positives as we go. The odds of decaying an already-set bit
// increases as the bloom filter saturates, so in the early hops of
// propagation this likely won't have any effect. This allows peers with
// bloom filter collisions to be reconsidered, but at positions on the
// network graph likely to be hops away from the original origin of the
// message.
for(unsigned int i=0;i<ZT_MULTICAST_BLOOM_FILTER_DECAY_RATE;++i)
bf.decay();
{
Mutex::Lock _l(_multicastMemberships_m);
@ -259,13 +269,15 @@ public:
// If it's not expired and it's from our random sample, add it to the set of peers
// to consider. Exclude immediate upstream and original submitter, since we know for
// a fact they've already seen this.
// a fact they've already seen this. Also exclude things in the bloom filter.
if ((channelMemberEntry->first != originalSubmitter)&&(channelMemberEntry->first != upstream)) {
P peer = topology.getPeer(channelMemberEntry->first);
if ((peer)&&(peer->hasActiveDirectPath(now))) {
toConsider[sampleSize++] = peer;
if (sampleSize >= ZT_MULTICAST_PICK_MAX_SAMPLE_SIZE)
break; // abort if we have enough candidates
if (!bf.contains(channelMemberEntry->first.sum())) {
P peer = topology.getPeer(channelMemberEntry->first);
if ((peer)&&(peer->hasActiveDirectPath(now))) {
toConsider[sampleSize++] = peer;
if (sampleSize >= ZT_MULTICAST_PICK_MAX_SAMPLE_SIZE)
break; // abort if we have enough candidates
}
}
}
++channelMemberEntry;
@ -282,22 +294,11 @@ public:
// switching."
std::sort(toConsider,toConsider + sampleSize,PeerPropagationPrioritySortOrder<P>());
// Decay a few random bits in bloom filter to probabilistically eliminate
// false positives as we go. The odds of decaying an already-set bit
// increases as the bloom filter saturates, so in the early hops of
// propagation this likely won't have any effect. This allows peers with
// bloom filter collisions to be reconsidered, but at positions on the
// network graph likely to be hops away from the original origin of the
// message.
for(unsigned int i=0;i<ZT_MULTICAST_BLOOM_FILTER_DECAY_RATE;++i)
bf.decay();
// Pick peers not in the bloom filter, setting bloom filter bits accordingly to
// remember and pass on these picks.
// Pick the best N peers
unsigned int picked = 0;
for(unsigned int i=0;((i<sampleSize)&&(picked < max));++i) {
if (!bf.set(toConsider[i]->address().sum()))
peers[picked++] = toConsider[i];
peers[picked++] = toConsider[i];
bf.set(toConsider[i]->address().sum());
}
// Add a supernode if there's nowhere else to go. Supernodes know of all multicast