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Improve NTP math

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This commit is contained in:
Eric Frias 2014-10-07 10:31:19 -04:00
parent 5a615e6b21
commit 0d61966a1c
1 changed files with 42 additions and 16 deletions
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58
src/network/ntp.cpp
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@ -23,7 +23,6 @@ namespace fc
fc::future<void> _read_loop_done;
udp_socket _sock;
uint32_t _request_interval_sec;
fc::time_point _last_request_time;
std::atomic_bool _last_ntp_delta_initialized;
std::atomic<int64_t> _last_ntp_delta_microseconds;
@ -45,6 +44,27 @@ namespace fc
_ntp_thread.quit(); //TODO: this can be removed once fc::threads call quit during destruction
}
fc::time_point ntp_timestamp_to_fc_time_point(uint64_t ntp_timestamp_net_order)
{
uint64_t ntp_timestamp_host = bswap_64(ntp_timestamp_net_order);
uint32_t fractional_seconds = ntp_timestamp_host & 0xffffffff;
uint32_t microseconds = (uint32_t)((((uint64_t)fractional_seconds * 1000000) + (UINT64_C(1) << 31)) >> 32);
uint32_t seconds_since_1900 = ntp_timestamp_host >> 32;
uint32_t seconds_since_epoch = seconds_since_1900 - 2208988800;
return fc::time_point() + fc::seconds(seconds_since_epoch) + fc::microseconds(microseconds);
}
uint64_t fc_time_point_to_ntp_timestamp(const fc::time_point& fc_timestamp)
{
uint64_t microseconds_since_epoch = (uint64_t)fc_timestamp.time_since_epoch().count();
uint32_t seconds_since_epoch = (uint32_t)(microseconds_since_epoch / 1000000);
uint32_t seconds_since_1900 = seconds_since_epoch + 2208988800;
uint32_t microseconds = microseconds_since_epoch % 1000000;
uint32_t fractional_seconds = (uint32_t)((((uint64_t)microseconds << 32) + (UINT64_C(1) << 31)) / 1000000);
uint64_t ntp_timestamp_net_order = ((uint64_t)seconds_since_1900 << 32) + fractional_seconds;
return bswap_64(ntp_timestamp_net_order);
}
void request_now()
{
assert(_ntp_thread.is_current());
@ -60,8 +80,9 @@ namespace fc
std::shared_ptr<char> send_buffer(new char[48], [](char* p){ delete[] p; });
std::array<unsigned char, 48> packet_to_send { {010,0,0,0,0,0,0,0,0} };
memcpy(send_buffer.get(), packet_to_send.data(), packet_to_send.size());
_last_request_time = fc::time_point::now();
_sock.send_to( send_buffer, packet_to_send.size(), ep );
uint64_t* send_buf_as_64_array = (uint64_t*)send_buffer.get();
send_buf_as_64_array[5] = fc_time_point_to_ntp_timestamp(fc::time_point::now()); // 5 = Transmit Timestamp
_sock.send_to(send_buffer, packet_to_send.size(), ep);
break;
}
}
@ -120,32 +141,37 @@ namespace fc
wlog("received ntp reply from ${from}",("from",from) );
} FC_RETHROW_EXCEPTIONS(error, "Error reading from NTP socket");
uint64_t receive_timestamp_net_order = recv_buf[4];
uint64_t receive_timestamp_host = bswap_64(receive_timestamp_net_order);
uint32_t fractional_seconds = receive_timestamp_host & 0xffffffff;
uint32_t microseconds = (uint32_t)(((((uint64_t)fractional_seconds) * 1000000) + (UINT64_C(1)<<31)) >> 32);
uint32_t seconds_since_1900 = receive_timestamp_host >> 32;
uint32_t seconds_since_epoch = seconds_since_1900 - 2208988800;
fc::time_point receive_time = fc::time_point::now();
fc::time_point origin_time = ntp_timestamp_to_fc_time_point(recv_buf[3]);
fc::time_point server_receive_time = ntp_timestamp_to_fc_time_point(recv_buf[4]);
fc::time_point server_transmit_time = ntp_timestamp_to_fc_time_point(recv_buf[5]);
fc::microseconds offset(((server_receive_time - origin_time) +
(server_transmit_time - receive_time)).count() / 2);
fc::microseconds round_trip_delay((receive_time - origin_time) -
(server_transmit_time - server_receive_time));
//wlog("origin_time = ${origin_time}, server_receive_time = ${server_receive_time}, server_transmit_time = ${server_transmit_time}, receive_time = ${receive_time}",
// ("origin_time", origin_time)("server_receive_time", server_receive_time)("server_transmit_time", server_transmit_time)("receive_time", receive_time));
wlog("ntp offset: ${offset}, round_trip_delay ${delay}", ("offset", offset)("delay", round_trip_delay));
//if the reply we just received has occurred more than a second after our last time request (it was more than a second ago since our last request)
if( fc::time_point::now() - _last_request_time > fc::seconds(1) )
if( round_trip_delay > fc::seconds(1) )
{
wlog("received stale ntp reply requested at ${request_time}, send a new time request",("request_time",_last_request_time));
wlog("received stale ntp reply requested at ${request_time}, send a new time request", ("request_time", origin_time));
request_now(); //request another reply and ignore this one
}
else //we think we have a timely reply, process it
{
auto ntp_time = (fc::time_point() + fc::seconds(seconds_since_epoch) + fc::microseconds(microseconds));
if( ntp_time - fc::time_point::now() < fc::seconds(60*60*24) &&
fc::time_point::now() - ntp_time < fc::seconds(60*60*24) )
if( offset < fc::seconds(60*60*24) && offset > fc::seconds(-60*60*24) )
{
_last_ntp_delta_microseconds = (ntp_time - fc::time_point::now()).count();
_last_ntp_delta_microseconds = offset.count();
_last_ntp_delta_initialized = true;
fc::microseconds ntp_delta_time = fc::microseconds(_last_ntp_delta_microseconds);
wlog("ntp_delta_time updated to ${delta_time}", ("delta_time",ntp_delta_time) );
}
else
elog( "NTP time and local time vary by more than a day! ntp:${ntp_time} local:${local}", ("ntp_time",ntp_time)("local",fc::time_point::now()) );
elog( "NTP time and local time vary by more than a day! ntp:${ntp_time} local:${local}",
("ntp_time", receive_time + offset)("local", fc::time_point::now()) );
}
}
} // try