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net: improve code documentation for dns seed behaviour

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This commit is contained in:
Anthony Towns 2020-05-28 10:07:49 +10:00
parent c19fd96694
commit 5cb7ee67a5
1 changed files with 19 additions and 4 deletions
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23
src/net.cpp
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@ -53,10 +53,17 @@ static constexpr std::chrono::minutes DUMP_PEERS_INTERVAL{15};
static constexpr int DNSSEEDS_TO_QUERY_AT_ONCE = 3;
/** How long to delay before querying DNS seeds
*
* If we have more than THRESHOLD entries in addrman, then it's likely
* that we got those addresses from having previously connected to the P2P
* network, and that we'll be able to successfully reconnect to the P2P
* network via contacting one of them. So if that's the case, spend a
* little longer trying to connect to known peers before querying the
* DNS seeds.
*/
static constexpr std::chrono::seconds DNSSEEDS_DELAY_FEW_PEERS{11}; // 11sec
static constexpr std::chrono::seconds DNSSEEDS_DELAY_MANY_PEERS{300}; // 5min
static constexpr int DNSSEEDS_DELAY_PEER_THRESHOLD = 1000; // "many" vs "few" peers -- you should only get this many if you've been on the live network
static constexpr std::chrono::seconds DNSSEEDS_DELAY_FEW_PEERS{11};
static constexpr std::chrono::minutes DNSSEEDS_DELAY_MANY_PEERS{5};
static constexpr int DNSSEEDS_DELAY_PEER_THRESHOLD = 1000; // "many" vs "few" peers
// We add a random period time (0 to 1 seconds) to feeler connections to prevent synchronization.
#define FEELER_SLEEP_WINDOW 1
@ -1595,6 +1602,8 @@ void CConnman::ThreadDNSAddressSeed()
seeds_right_now = seeds.size();
} else if (addrman.size() == 0) {
// If we have no known peers, query all.
// This will occur on the first run, or if peers.dat has been
// deleted.
seeds_right_now = seeds.size();
}
@ -1620,6 +1629,9 @@ void CConnman::ThreadDNSAddressSeed()
LogPrintf("Waiting %d seconds before querying DNS seeds.\n", seeds_wait_time.count());
std::chrono::seconds to_wait = seeds_wait_time;
while (to_wait.count() > 0) {
// if sleeping for the MANY_PEERS interval, wake up
// early to see if we have enough peers and can stop
// this thread entirely freeing up its resources
std::chrono::seconds w = std::min(DNSSEEDS_DELAY_FEW_PEERS, to_wait);
if (!interruptNet.sleep_for(w)) return;
to_wait -= w;
@ -1646,7 +1658,7 @@ void CConnman::ThreadDNSAddressSeed()
if (interruptNet) return;
// hold off on querying seeds if p2p network deactivated
// hold off on querying seeds if P2P network deactivated
if (!fNetworkActive) {
LogPrintf("Waiting for network to be reactivated before querying DNS seeds.\n");
do {
@ -1797,6 +1809,9 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
return;
// Add seed nodes if DNS seeds are all down (an infrastructure attack?).
// Note that we only do this if we started with an empty peers.dat,
// (in which case we will query DNS seeds immediately) *and* the DNS
// seeds have not returned any results.
if (addrman.size() == 0 && (GetTime() - nStart > 60)) {
static bool done = false;
if (!done) {