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author | 2008-11-13 09:49:11 +0000 | |
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committer | 2008-11-13 09:49:11 +0000 | |
commit | e44a7e37b6c7b5961adaffc62b9042b8d442938e (patch) | |
tree | 95b67c356e93163467db2451f2b8cce84ed5d582 /includes/js/dojox/cometd/timesync.js | |
parent | a62b9742ee5e28bcec6872d88f50f25b820914f6 (diff) | |
download | scuttle-e44a7e37b6c7b5961adaffc62b9042b8d442938e.tar.gz scuttle-e44a7e37b6c7b5961adaffc62b9042b8d442938e.zip |
New feature: basic Ajax suggestion for tags and implementation of Dojo toolkit
git-svn-id: https://semanticscuttle.svn.sourceforge.net/svnroot/semanticscuttle/trunk@151 b3834d28-1941-0410-a4f8-b48e95affb8f
Diffstat (limited to 'includes/js/dojox/cometd/timesync.js')
-rw-r--r-- | includes/js/dojox/cometd/timesync.js | 126 |
1 files changed, 126 insertions, 0 deletions
diff --git a/includes/js/dojox/cometd/timesync.js b/includes/js/dojox/cometd/timesync.js new file mode 100644 index 0000000..44ef241 --- /dev/null +++ b/includes/js/dojox/cometd/timesync.js @@ -0,0 +1,126 @@ +if(!dojo._hasResource["dojox.cometd.timesync"]){ //_hasResource checks added by build. Do not use _hasResource directly in your code. +dojo._hasResource["dojox.cometd.timesync"] = true; +dojo.provide("dojox.cometd.timesync"); +dojo.require("dojox.cometd"); + +/** + * this file provides the time synchronization extension to cometd. + * Timesync allows the client and server to exchange time information on every + * handshake and connect message so that the client may calculate an approximate + * offset from it's own clock epoch to that of the server. + * + * With each handshake or connect, the extension sends timestamps within the + * ext field like: {ext:{timesync:{tc:12345567890},...},...} + * where ts is the timestamp in ms since 1970 of when the message was sent. + * + * A cometd server that supports timesync, should respond with and ext field + * like: {ext:{timesync:{tc:12345567890,ts:1234567900,p:123},...},...} + * where ts is the timestamp sent by the client, te is the timestamp on the server + * of when the message was received and p is the poll duration in ms - ie the + * time the server took before sending the response. + * + * On receipt of the response, the client is able to use current time to determine + * the total trip time, from which p is subtracted to determine an approximate + * two way network traversal time. The assumption is made that the network is + * symmetric for traversal time, so the offset between the two clocks is + * ts-tc-(now-tc-p)/2. In practise networks (and the cometd client/server software) + * is never perfectly symmetric, so accuracy is limited by the difference, which + * can be 10s of milliseconds. + * + * In order to smooth over any transient fluctuations, the extension keeps a sliding + * average of the offsets received. By default this is over 10 messages, but this can + * be changed with the dojox.cometd.timesync._window element. + */ +dojox.cometd.timesync= new function(){ + + this._window=10;// The window size for the sliding average of offset samples. + this._minWindow=4;// The window size for the sliding average of offset samples. + this._offsets=new Array(); // The samples used to calculate the average offset. + this.offset=0; // The offset in ms between the clients clock and the servers clock. Add this to the local + // time epoch to obtain server time. + this.samples=0; // The number of samples used to calculate the offset. If 0, the offset is not valid. + + this.getServerTime=function(){ // return: long + // Summary: + // Calculate the current time on the server + // + return new Date().getTime()+this.offset; + } + + this.getServerDate=function(){ // return: Date + // Summary: + // Calculate the current time on the server + // + return new Date(this.getServerTime()); + } + + this.setTimeout=function(/*function*/call,/*long|Date*/atTimeOrDate){ + // Summary: + // Set a timeout function relative to server time + // call: + // the function to call when the timeout occurs + // atTimeOrTime: + // a long timestamp or a Date representing the server time at + // which the timeout should occur. + + var ts=(atTimeOrDate instanceof Date)?atTimeOrDate.getTime():(0+atTimeOrDate); + var tc=ts-this.offset; + var interval=tc-new Date().getTime(); + if (interval<=0) + interval=1; + return setTimeout(call,interval); + } + + this._in=function(/*Object*/msg){ + // Summary: + // Handle incoming messages for the timesync extension. + // description: + // Look for ext:{timesync:{}} field and calculate offset if present. + // msg: + // The incoming bayeux message + + var channel=msg.channel; + if (channel && channel.indexOf('/meta/')==0){ + if (msg.ext && msg.ext.timesync){ + var sync=msg.ext.timesync; + var now=new Date().getTime(); + + this._offsets.push(sync.ts-sync.tc-(now-sync.tc-sync.p)/2); + if (this._offsets.length>this._window) + this._offsets.shift(); + this.samples++; + var total=0; + for (var i in this._offsets) + total+=this._offsets[i]; + this.offset=parseInt((total/this._offsets.length).toFixed()); + + if (this.samples<this._minWindow) + setTimeout(dojox._scopeName + ".cometd.publish('/meta/ping',null)",100); + } + } + return msg; + } + + this._out=function(msg){ + // Summary: + // Handle outgoing messages for the timesync extension. + // description: + // Look for handshake and connect messages and add the ext:{timesync:{}} fields + // msg: + // The outgoing bayeux message + + var channel=msg.channel; + if (channel && channel.indexOf('/meta/')==0){ + var now=new Date().getTime(); + if (!msg.ext) + msg.ext={}; + msg.ext.timesync={tc: now}; + } + return msg; + } +}; + +dojox.cometd._extendInList.push(dojo.hitch(dojox.cometd.timesync,"_in")); +dojox.cometd._extendOutList.push(dojo.hitch(dojox.cometd.timesync,"_out")); + +} |