javascript - Efficient closure structure in node.js -

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i'm starting write server in node.js , wondering whether or not i'm doing things right way...

basically structure following pseudocode:

function processstatus(file, data, status) { ... }  function gotdbinfo(dbinfo) {     var myfile = dbinfo.file;     function gotfileinfo(fileinfo) {         var contents = fileinfo.contents;         function sentmessage(status) {             processstatus(myfile, contents, status);         }         sendmessage(myfile.name + contents, sentmessage);     }     checkfile(myfile, gotfileinfo); } checkdb(query, gotdbinfo);

in general, i'm wondering if right way code node.js, , more specifically:

1) vm smart enough run "concurrently" (i.e. switch contexts) between each callback not hung lots of connected clients?

2) when garbage collection run, clear memory if last callback (processstatus) finished?

  1. node.js event-based, codes handlers of events. v8 engine execute-to-end synchronous code in handler , process next event.

    async call (network/file io) post event thread blocking io (that's in libev libeio afaik, may wrong on this). app can handle other clients. when io task done, event fired , callback function called upon.

    here's example of aync call flow, simulating node app handling client request:

    onrequest(req, res) {     // have io , cpu intensive task before responding client      asynccall(function callback1() {         // callback1() trigger after asynccall() done it's part         // *note other code might have been executed in between*          moreasynccall(function callback2(data) {             // callback2() trigger after moreasynccall() done it's part             // note other code might have been executed in between              // res in scope closure             res.end(data);              // callback2() returns here, node can execute other code             // client should receive response             // tcp connection may kept alive though         });          // callback1() returns here, node can execute other code         // have done processing of asynccall() synchronously          // in callback1(), block long          // used moreasynccall() *yield other code*         // kind of cooperative scheduling     });      // tasks scheduled calling asynccall()     // onrequest() returns here, node can execute other code }

  2. when v8 not have enough memory, garbage collection. knows whether chunk of memory reachable live javascript object. i'm not sure if aggressively clean memory upon reaching end of function.

references:

this google i/o presentation discussed gc mechanism of chrome (hence v8).

http://platformjs.wordpress.com/2010/11/24/node-js-under-the-hood/

http://blog.zenika.com/index.php?post/2011/04/10/nodejs


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