- All Implemented Interfaces:
BayeuxServer.Extension
Timesync extension (server side).
With each handshake or connect, the extension sends timestamps within the ext
field like: {ext:{timesync:{tc:12345567890,l:23,o:4567},...},...}
where:
- tc is the client timestamp in ms since 1970 of when the message was sent.
- l is the network lag that the client has calculated.
- o is the clock offset that the client has calculated.
A CometD server that supports timesync, can respond with an ext field like:
{ext:{timesync:{tc:12345567890,ts:1234567900,p:123,a:3},...},...}
where:
- tc is the client timestamp of when the message was sent,
- ts is the server timestamp of when the message was received
- p is the poll duration in ms - ie the time the server took before sending the response.
- a is the measured accuracy of the calculated offset and lag sent by the client
The relationship between tc, ts, o and l on the server is given by
ts=tc+o+l
(the time the server received the message is the
client time plus the offset plus the network lag). Thus the accuracy of the o
and l settings can be determined with a=tc+o+l-ts
.
When the client has received the response, it can make a more accurate
estimate of the lag as l2=(now-tc-p)/2
(assuming symmetric lag).
A new offset can then be calculated with the relationship on the client that
ts=tc+o2+l2
, thus o2=ts-tc-l2
.
Since the client also receives the a value calculated on the server, it should be possible to analyse this and compensate for some asymmetry in the lag. But the current client does not do this.
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Field Summary
Fields -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionint
timesync responses are not set if the measured accuracy is less than the accuracyTarget.boolean
rcvMeta
(ServerSession from, ServerMessage.Mutable message) Blocking version ofBayeuxServer.Extension.incoming(ServerSession, ServerMessage.Mutable, Promise)
for meta messages.boolean
sendMeta
(ServerSession session, ServerMessage.Mutable message) Blocking version ofBayeuxServer.Extension.outgoing(ServerSession, ServerSession, ServerMessage.Mutable, Promise)
for meta messages.void
setAccuracyTarget
(int target) timesync responses are not set if the measured accuracy is less than the accuracyTarget.Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface org.cometd.bayeux.server.BayeuxServer.Extension
incoming, outgoing, rcv, send
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Field Details
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LAG_ATTRIBUTE
- See Also:
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Constructor Details
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TimesyncExtension
public TimesyncExtension()
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Method Details
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getAccuracyTarget
public int getAccuracyTarget()timesync responses are not set if the measured accuracy is less than the accuracyTarget.- Returns:
- accuracy target in ms (default 25ms)
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setAccuracyTarget
public void setAccuracyTarget(int target) timesync responses are not set if the measured accuracy is less than the accuracyTarget.- Parameters:
target
- accuracy target in ms
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rcvMeta
Description copied from interface:BayeuxServer.Extension
Blocking version of
BayeuxServer.Extension.incoming(ServerSession, ServerMessage.Mutable, Promise)
for meta messages.- Specified by:
rcvMeta
in interfaceBayeuxServer.Extension
- Parameters:
from
- the session that sent the messagemessage
- the incoming message- Returns:
- whether message processing should continue
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sendMeta
Description copied from interface:BayeuxServer.Extension
Blocking version of
BayeuxServer.Extension.outgoing(ServerSession, ServerSession, ServerMessage.Mutable, Promise)
for meta messages.- Specified by:
sendMeta
in interfaceBayeuxServer.Extension
- Parameters:
session
- the session the message is sent to, or null for a publish.message
- the outgoing message- Returns:
- whether message processing should continue
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