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Make CAddrman::Select_ select buckets, not positions, first

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The original CAddrMan behaviour (before commit
e6b343d880) was to pick a uniformly
random non-empty bucket, and then pick a random element from that
bucket. That commit, which introduced deterministic placement
of entries in buckets, changed this to picking a uniformly random
non-empty bucket position instead.

This commit reverts the original high-level behavior, but in the
deterministic placement model.
This commit is contained in:
Pieter Wuille 2021-09-29 16:22:44 -04:00
parent 113b863f07
commit 632aad9e6d
1 changed files with 24 additions and 8 deletions
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32
src/addrman.cpp
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@ -709,38 +709,54 @@ std::pair<CAddress, int64_t> AddrManImpl::Select_(bool newOnly) const
// use a tried node
double fChanceFactor = 1.0;
while (1) {
// Pick a tried bucket, and an initial position in that bucket.
int nKBucket = insecure_rand.randrange(ADDRMAN_TRIED_BUCKET_COUNT);
int nKBucketPos = insecure_rand.randrange(ADDRMAN_BUCKET_SIZE);
while (vvTried[nKBucket][nKBucketPos] == -1) {
nKBucket = (nKBucket + insecure_rand.randbits(ADDRMAN_TRIED_BUCKET_COUNT_LOG2)) % ADDRMAN_TRIED_BUCKET_COUNT;
nKBucketPos = (nKBucketPos + insecure_rand.randbits(ADDRMAN_BUCKET_SIZE_LOG2)) % ADDRMAN_BUCKET_SIZE;
// Iterate over the positions of that bucket, starting at the initial one,
// and looping around.
int i;
for (i = 0; i < ADDRMAN_BUCKET_SIZE; ++i) {
if (vvTried[nKBucket][(nKBucketPos + i) % ADDRMAN_BUCKET_SIZE] != -1) break;
}
int nId = vvTried[nKBucket][nKBucketPos];
// If the bucket is entirely empty, start over with a (likely) different one.
if (i == ADDRMAN_BUCKET_SIZE) continue;
// Find the entry to return.
int nId = vvTried[nKBucket][(nKBucketPos + i) % ADDRMAN_BUCKET_SIZE];
const auto it_found{mapInfo.find(nId)};
assert(it_found != mapInfo.end());
const AddrInfo& info{it_found->second};
// With probability GetChance() * fChanceFactor, return the entry.
if (insecure_rand.randbits(30) < fChanceFactor * info.GetChance() * (1 << 30)) {
return {info, info.nLastTry};
}
// Otherwise start over with a (likely) different bucket, and increased chance factor.
fChanceFactor *= 1.2;
}
} else {
// use a new node
double fChanceFactor = 1.0;
while (1) {
// Pick a new bucket, and an initial position in that bucket.
int nUBucket = insecure_rand.randrange(ADDRMAN_NEW_BUCKET_COUNT);
int nUBucketPos = insecure_rand.randrange(ADDRMAN_BUCKET_SIZE);
while (vvNew[nUBucket][nUBucketPos] == -1) {
nUBucket = (nUBucket + insecure_rand.randbits(ADDRMAN_NEW_BUCKET_COUNT_LOG2)) % ADDRMAN_NEW_BUCKET_COUNT;
nUBucketPos = (nUBucketPos + insecure_rand.randbits(ADDRMAN_BUCKET_SIZE_LOG2)) % ADDRMAN_BUCKET_SIZE;
// Iterate over the positions of that bucket, starting at the initial one,
// and looping around.
int i;
for (i = 0; i < ADDRMAN_BUCKET_SIZE; ++i) {
if (vvNew[nUBucket][(nUBucketPos + i) % ADDRMAN_BUCKET_SIZE] != -1) break;
}
int nId = vvNew[nUBucket][nUBucketPos];
// If the bucket is entirely empty, start over with a (likely) different one.
if (i == ADDRMAN_BUCKET_SIZE) continue;
// Find the entry to return.
int nId = vvNew[nUBucket][(nUBucketPos + i) % ADDRMAN_BUCKET_SIZE];
const auto it_found{mapInfo.find(nId)};
assert(it_found != mapInfo.end());
const AddrInfo& info{it_found->second};
// With probability GetChance() * fChanceFactor, return the entry.
if (insecure_rand.randbits(30) < fChanceFactor * info.GetChance() * (1 << 30)) {
return {info, info.nLastTry};
}
// Otherwise start over with a (likely) different bucket, and increased chance factor.
fChanceFactor *= 1.2;
}
}