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Improvements to NetAssociation ..
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.. simplify the good/bad response processing
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gavineadie@gmail.com committed Feb 11, 2011
1 parent 7eb36ab commit a12a0a9
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Showing 3 changed files with 73 additions and 47 deletions.
8 changes: 4 additions & 4 deletions Classes/NetAssociation.h
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Original file line number Diff line number Diff line change
Expand Up @@ -52,10 +52,7 @@ struct ntpShortTime {

NSTimer * repeatingTimer; // fires off an ntp request ...
int pollingIntervalIndex; // index into polling interval table

NSMutableArray * fifoQueue;
NSUInteger answerCount, trustyCount;


struct ntpTimestamp ntpClientSendTime,
ntpServerRecvTime,
ntpServerSendTime,
Expand All @@ -67,6 +64,9 @@ struct ntpShortTime {

int li, vn, mode, stratum, poll, prec, refid;

double fifoQueue[8];
short fifoIndex;

}

@property (readonly) BOOL trusty; // is this clock trustworthy
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102 changes: 63 additions & 39 deletions Classes/NetAssociation.m
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@

static double pollIntervals[18] = {
16.0, 16.0, 16.0, 16.0, 16.0, 35.0,
72.0, 150.0, 256.0, 512.0, 1024.0, 2048.0,
72.0, 127.0, 258.0, 511.0, 1024.0, 2048.0,
4096.0, 8192.0, 16384.0, 32768.0, 65536.0, 131072.0
};

Expand Down Expand Up @@ -64,7 +64,6 @@ - (id) init:(NSString *) serverName {
pollingIntervalIndex = 4;
trusty = FALSE; // don't trust this clock to start with ...
offset = 0.0; // start with clock on time (no offset)
answerCount = trustyCount = 0;
/*┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│ Create a UDP socket that will communicate with the time server and set its delegate ... │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘*/
Expand All @@ -76,7 +75,8 @@ - (id) init:(NSString *) serverName {
│ the server we push it into the fifo. We sample the contents of the fifo for quality and, if it │
│ meets our standards we use the contents of the fifo to obtain a weighted average of the times. │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘*/
fifoQueue = [[NSMutableArray arrayWithCapacity:8] retain];
for (short i = 0; i < 8; i++) fifoQueue[i] = 1E10; // set fifo to all empty
fifoIndex = 0;
/*┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│ Finally, initialize the repeating timer that queries the server, set it's trigger time to the │
│ infinite future, and put it on the run loop .. nothing will happen (yet) │
Expand Down Expand Up @@ -176,62 +176,87 @@ - (NSData *) createPacket {
}

- (void) evaluatePacket {
double packetOffset = 0.0; // initial untrustworthy offset
// NTP_Logging(@"%@", [self prettyPrintPacket]);
/*┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│ determine the quality of this particular time .. │
│ .. if max_error is less than 50mS (and not zero) AND │
│ .. stratum > 0 AND │
│ .. the mode is 4 (packet came from server) AND │
│ .. the server clock was set less than 1 hour ago │
│ the packet is trustworthy. │
│ the packet is trustworthy -- compute and store offset in 8-slot fifo ... │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘*/
trusty = (dispersion > 0.1 && dispersion < 50.0) && (stratum > 0) && (mode == 4) &&
(-[[self dateFromNetworkTime:&ntpServerBaseTime] timeIntervalSinceNow] < 3600.0);

if (trusty) {
trustyCount++;

if ((dispersion > 0.1 && dispersion < 50.0) && (stratum > 0) && (mode == 4) &&
(-[[self dateFromNetworkTime:&ntpServerBaseTime] timeIntervalSinceNow] < 3600.0)) {
el_time=ntpDiffSeconds(&ntpClientSendTime, &ntpClientRecvTime); // .. (T4-T1)
st_time=ntpDiffSeconds(&ntpServerRecvTime, &ntpServerSendTime); // .. (T3-T2)
skew1 = ntpDiffSeconds(&ntpServerSendTime, &ntpClientRecvTime); // .. (T2-T1)
skew2 = ntpDiffSeconds(&ntpServerRecvTime, &ntpClientSendTime); // .. (T3-T4)

if ([fifoQueue count] == 8) {
[fifoQueue removeObjectAtIndex:0];
}
[fifoQueue addObject:[NSNumber numberWithDouble:(skew1+skew2)/2.0]];

offset = [[fifoQueue valueForKeyPath:@"@avg.doubleValue"] doubleValue];
packetOffset = (skew1+skew2)/2.0; // calulate trustworthy offset
}

// NTP_Logging(@"evaluatePacket: [%@] - %@ - offset±dispersion: %5.3fs±%5.3fmS (%i - %i/%i)",
// server, trusty ? @"GOOD" : @"FAIL", offset, dispersion,
// [fifoQueue count], answerCount, trustyCount);
fifoQueue[fifoIndex % 8] = packetOffset; // store offset
fifoIndex++; // rotate index

NTP_Logging(@"[%@] index=%i {%5.3f,%5.3f,%5.3f,%5.3f,%5.3f,%5.3f,%5.3f,%5.3f}", server,
fifoIndex % 8, fifoQueue[0], fifoQueue[1], fifoQueue[2], fifoQueue[3],
fifoQueue[4], fifoQueue[5], fifoQueue[6], fifoQueue[7]);
/*┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│ look at the collection of association's offsets and make some determination of their worth │
│ .. if we have four or more average zero offsets, we're not getting replies │
│ .. if we're not 'trusty' for more than half the queries, the server is wonky │
│ tell anyone who cares that we're out of the game ... │
│ look at the (up to eight) offsets in the fifo and and count 'good', 'fail' and 'not used yet' │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘*/
if (answerCount > 3 && fabs(offset) < 1.e-6 || (trustyCount > 0 && answerCount/trustyCount > 1))
[[NSNotificationCenter defaultCenter] postNotificationName:@"assoc-fail" object:self];
else {
[[NSNotificationCenter defaultCenter] postNotificationName:@"assoc-good" object:self];
short good = 0, fail = 0, none = 0;
offset = 0.0;
for (short i = 0; i < 8; i++) {
if (fifoQueue[i] > 1E9) { // fifo slot is unused
none++;
continue;
}
if (fabs(fifoQueue[i]) < 1E-6) { // server can't be trusted
fail++;
}
else {
good++;
offset += fifoQueue[i];
}
}
/*┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│ if the association is behaving well, we can increase its polling interval ... │
│ .. if we have at least one 'good' server response or four or more 'fail' responses, we'll │
│ inform our management accordingly. If we have less than four 'fails' we won't make any │
│ note of that ... we won't condemn a server until we get four 'fail' packets. │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘*/
pollingIntervalIndex = 7 - stratum;
if ([repeatingTimer timeInterval] != pollIntervals[pollingIntervalIndex]) {
// NTP_Logging(@"[%@] poll interval adusted: %3.1f >> %3.1f", server,
// [repeatingTimer timeInterval], pollIntervals[pollingIntervalIndex]);
[repeatingTimer invalidate];
repeatingTimer = nil;
repeatingTimer = [NSTimer scheduledTimerWithTimeInterval:pollIntervals[pollingIntervalIndex]
target:self selector:@selector(queryTimeServer:)
userInfo:nil repeats:YES];
if (good > 0 || fail > 3) {
offset = offset / good;

NTP_Logging(@"[%@] index=%i {good: %i; fail: %i; none: %i} offset=%3.1f", server,
fifoIndex, good, fail, none, offset * 1000.0);

if (good+none < 5) { // four or more 'fails'
trusty = FALSE;
[[NSNotificationCenter defaultCenter] postNotificationName:@"assoc-fail" object:self];
}
else { // ...
trusty = TRUE;
[[NSNotificationCenter defaultCenter] postNotificationName:@"assoc-good" object:self];
}
}

/*┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│ .. if the association is providing times which don't vary much, we could increase its polling │
│ interval. In practice, once things settle down, the standard deviation on any time server │
│ seems to fall in the 70-120mS range (plenty close for our work). We usually pick up a few │
│ stratum=1 servers, it would be a Good Thing to not hammer those so hard ... │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘*/
if (stratum == 1) pollingIntervalIndex = 6;
if (stratum == 2) pollingIntervalIndex = 5;
if ([repeatingTimer timeInterval] != pollIntervals[pollingIntervalIndex]) {
NTP_Logging(@"[%@] poll interval adusted: %3.1f >> %3.1f", server,
[repeatingTimer timeInterval], pollIntervals[pollingIntervalIndex]);
[repeatingTimer invalidate];
repeatingTimer = nil;
repeatingTimer = [NSTimer scheduledTimerWithTimeInterval:pollIntervals[pollingIntervalIndex]
target:self selector:@selector(queryTimeServer:)
userInfo:nil repeats:YES];
}
}

#pragma mark N e t w o r k • C a l l b a c k s
Expand Down Expand Up @@ -284,7 +309,6 @@ - (BOOL) onUdpSocket:(AsyncUdpSocket *)sender didReceiveData:(NSData *)data
ntpServerSendTime.fullSeconds = ntohl(hostData[10]);
ntpServerSendTime.partSeconds = ntohl(hostData[11]);

answerCount++;
[self evaluatePacket];

return YES;
Expand Down
10 changes: 6 additions & 4 deletions Classes/NetworkClock.m
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Original file line number Diff line number Diff line change
Expand Up @@ -238,30 +238,32 @@ - (void) associationTrue:(NSNotification *) notification {
}

/*┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ associationFail -- notification from an association that became a 'falseticker' ┃
┃ associationFake -- notification from an association that became a 'falseticker' ┃
┃ .. if we already have 8 associations in play, drop this one. ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛*/
- (void) associationFake:(NSNotification *) notification {
if ([timeAssociations count] > 8) {
NetAssociation * association = [notification object];
NTP_Logging(@"*** false association: %@ (%i left)", association, [timeAssociations count]);
[association finish];
[timeAssociations removeObject:association];
[association finish];
association = nil;
}
}

/*┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ applicationBack -- catch the notification when the application goes into the background ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛*/
- (void) applicationBack:(NSNotification *) notification {
NTP_Logging(@"*** application -> Background");
LogInProduction(@"*** application -> Background");
// [self finishAssociations];
}

/*┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ applicationFore -- catch the notification when the application comes out of the background ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛*/
- (void) applicationFore:(NSNotification *) notification {
NTP_Logging(@"*** application -> Foreground");
LogInProduction(@"*** application -> Foreground");
// [self enableAssociations];
}

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