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Track circuit occupancy with no alteration to signalling

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Track circuit occupancy with no alteration to signalling 27/11/2013 at 21:22 #52080
CTCThiago
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Hello Guys,

In a multiplayer session, i see a TC Occupied with no alteration in signalling, but others players not (I'm in client).

note: this is not a train.

This is a bug or it happens to you anytime before?

Cheers Thiago.

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Last edited: 27/11/2013 at 21:22 by CTCThiago
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Track circuit occupancy with no alteration to signalling 27/11/2013 at 21:41 #52081
JamesN
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Potential Bug, under investigation
Last edited: 27/11/2013 at 21:46 by JamesN
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Track circuit occupancy with no alteration to signalling 27/11/2013 at 22:26 #52083
AndyG
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1830 posts
Most likely to be a connection glitch, with some loss of data.

Note that the signal in rear of the red TC is still showing a proceed aspect, which implies that the host server is still correct.

It should get back into synchronization when the next real train passes through.

I've encountered it a couple of times as a client, seems to be related to weak/slow connections, or when another client connects.

I can only help one person a day. Today's not your day. Tomorrow doesn't look too good either.
Last edited: 27/11/2013 at 22:29 by AndyG
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Track circuit occupancy with no alteration to signalling 28/11/2013 at 02:08 #52090
Temple Meads
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I noticed last night, while in a KX MP game, that some small elements of the white 'route set' indicators on track circuits were still showing as 'route set', even though no route was set over them, setting a new route cured it though.

Is this likely to also be a connection glitch?

Username TIM in multiplayer
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Track circuit occupancy with no alteration to signalling 28/11/2013 at 05:19 #52093
alvinhochun
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" said:
Most likely to be a connection glitch, with some loss of data.

Doesn't SimSig use TCP? I think TCP is stream-oriented and has built-in ack mechanism to make sure data is transmitted in order so no data can be lost.

_ _ _ _,_ _ _ _! (censored by the Hong Kong national security law)
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Track circuit occupancy with no alteration to signalling 28/11/2013 at 09:03 #52098
sorabain
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TCP wont help if the connection is dropped and re-established via a new socket on the client-side; then you need some additional application-level sequencing to notice and set about filling the gap.

Not particularly familiar with this sim but funny how there's a double yellow preceding a green too.. i guess the double yellow is correct and the green should be single yellow, then red just before the occupied TC etc

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Track circuit occupancy with no alteration to signalling 28/11/2013 at 09:26 #52099
postal
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" said:
I noticed last night, while in a KX MP game, that some small elements of the white 'route set' indicators on track circuits were still showing as 'route set', even though no route was set over them, setting a new route cured it though.

Is this likely to also be a connection glitch?
I presume this is not the same as white elements showing over points where no route is set to indicate that they are flank-locked by a movement on an adjacent line.

“In life, there is always someone out there, who won’t like you, for whatever reason, don’t let the insecurities in their lives affect yours.” – Rashida Rowe
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Track circuit occupancy with no alteration to signalling 28/11/2013 at 15:36 #52106
Stephen Fulcher
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The signal showing the "wrong" YY aspect could also be a symptom of AndyG's theory.

If the host computer is correct, then it is likely not a bug with the sim. Like Andy, I have seen some strange indications as a client that the host has reported are normal.

Out of interest, did every client see this phenomenon or just the one?

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Track circuit occupancy with no alteration to signalling 28/11/2013 at 16:18 #52108
Temple Meads
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" said:
" said:
I noticed last night, while in a KX MP game, that some small elements of the white 'route set' indicators on track circuits were still showing as 'route set', even though no route was set over them, setting a new route cured it though.

Is this likely to also be a connection glitch?
I presume this is not the same as white elements showing over points where no route is set to indicate that they are flank-locked by a movement on an adjacent line.
Nope, this appeared to be random, and I can't say I've ever noticed it before.

Will grab a screenshot if I notice it again.

Username TIM in multiplayer
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Track circuit occupancy with no alteration to signalling 28/11/2013 at 16:23 #52110
GeoffM
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" said:
In a multiplayer session, i see a TC Occupied with no alteration in signalling, but others players not (I'm in client).
I read this as the OP was the only person to have this track showing occupied, i.e. other clients and the server showed correctly. Therefore I would assume there was a missed message somehow. TCP is fairly reliable but it's not perfect, particularly if a particular hop is busy.

SimSig Boss
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Track circuit occupancy with no alteration to signalling 29/11/2013 at 12:54 #52142
clive
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" said:

TCP is fairly reliable but it's not perfect, particularly if a particular hop is busy.
TCP is a lot more reliable than these sort of rates imply. I suspect there's an issue with the Delphi TCP stack, but no investigations have been done yet.

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Track circuit occupancy with no alteration to signalling 29/11/2013 at 14:26 #52147
alvinhochun
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" said:
I suspect there's an issue with the Delphi TCP stack

I guess the chance of this is not very high, a major bug in a major runtime library which could have already affected a lot of people but yet to be found?

" said:
TCP wont help if the connection is dropped and re-established via a new socket on the client-side; then you need some additional application-level sequencing to notice and set about filling the gap.

Not sure but I've never seen SimSig client automatically reconnect to the server when connection is lost.

_ _ _ _,_ _ _ _! (censored by the Hong Kong national security law)
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Track circuit occupancy with no alteration to signalling 03/12/2013 at 16:15 #52357
clive
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" said:
" said:
I suspect there's an issue with the Delphi TCP stack

I guess the chance of this is not very high, a major bug in a major runtime library which could have already affected a lot of people but yet to be found?
True, but I can't see where else the problem could be.

To investigate properly requires finding an environment where these problems happen and then running a TCP sniffer on the link. Then I could analyze the logs to find out what's going wrong. But without that or a smoking gun I don't know where we go next.

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Track circuit occupancy with no alteration to signalling 03/12/2013 at 17:42 #52366
GeoffM
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" said:
" said:

TCP is fairly reliable but it's not perfect, particularly if a particular hop is busy.
TCP is a lot more reliable than these sort of rates imply. I suspect there's an issue with the Delphi TCP stack, but no investigations have been done yet.
The Delphi side of things is mostly just a wrapper for Windows calls.

All I meant by my reference was that if, for example, you're hammering your broadband connection then the chances of packets being dropped increases. We're talking two home networks and a whole bunch of routing between the UK and Brazil in this particular case.

:evil: Maybe the NSA corrupted a packet? :silly:

SimSig Boss
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Track circuit occupancy with no alteration to signalling 03/12/2013 at 17:55 #52367
sorabain
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Is the front end entirely single-threaded? Wondering if it could be due to unsynchronized reading/writing of the same fields across multiple threads. I have all sorts of "fun" with memory barriers at work...
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Track circuit occupancy with no alteration to signalling 03/12/2013 at 18:55 #52369
AndyG
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" said:
....All I meant by my reference was that if, for example, you're hammering your broadband connection then the chances of packets being dropped increases. We're talking two home networks and a whole bunch of routing between the UK and Brazil in this particular case.

:evil: Maybe the NSA corrupted a packet? :silly:
I also think it's to do with a busy network.
Once as a client on Bristol, I had several instances fairly close together, could be associated with another client connecting, and another symptom can be a short hang, or freeze-up which is usually followed by a disconnection[sup]1[/sup].

I suspect the likes of a Skype/Teamspeak connection doesn't help the cause either.

[sup]1[/sup] The reload time on a loader sim is a nuisance here, could do with a straight 'reconnect' maybe?

I can only help one person a day. Today's not your day. Tomorrow doesn't look too good either.
Last edited: 03/12/2013 at 18:56 by AndyG
Reason: typo

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Track circuit occupancy with no alteration to signalling 03/12/2013 at 19:29 #52370
GeoffM
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" said:
Is the front end entirely single-threaded? Wondering if it could be due to unsynchronized reading/writing of the same fields across multiple threads. I have all sorts of "fun" with memory barriers at work...
The data is read from the socket and then put into a queue. The main thread then picks up the messages off the queue. However, I do see an extra thing I can do just to be certain.


" said:
The reload time on a loader sim is a nuisance here, could do with a straight 'reconnect' maybe?
Already on the list (reconnect); however, some testers have a version that reportedly loads up in half the time of 4.0.14, and in some cases even better than that.

SimSig Boss
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Track circuit occupancy with no alteration to signalling 05/12/2013 at 09:06 #52420
alvinhochun
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" said:
To investigate properly requires finding an environment where these problems happen and then running a TCP sniffer on the link. Then I could analyze the logs to find out what's going wrong. But without that or a smoking gun I don't know where we go next.

Perhaps you can add an option in SimSig to dump the TCP stream and do it on both the client and server, then later compare them to see if they match?
This require some extra coding, but should make it easier for normal users to help debugging.

_ _ _ _,_ _ _ _! (censored by the Hong Kong national security law)
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Track circuit occupancy with no alteration to signalling 05/12/2013 at 17:59 #52436
Forest Pines
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Or just work out suitable instructions for getting testers to run Wireshark with consistent settings and get them to send the logs in!
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Track circuit occupancy with no alteration to signalling 06/12/2013 at 13:01 #52468
clive
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" said:
" said:
To investigate properly requires finding an environment where these problems happen and then running a TCP sniffer on the link. Then I could analyze the logs to find out what's going wrong. But without that or a smoking gun I don't know where we go next.

Perhaps you can add an option in SimSig to dump the TCP stream and do it on both the client and server, then later compare them to see if they match?
This require some extra coding, but should make it easier for normal users to help debugging.
That might be a later stage, but getting over-the-wire logs is less intrusive and gives us a clue as to where the problem lies. For example, the logs you describe won't distinguish between a message not sent and one lost in transit without TCP realizing. A wire log will tell us which end lost the message.

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