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High concurrency writes leads to data loss

See original GitHub issue

testing script

$ cat winston.js 
var winston = require('winston');

var logger = new (winston.Logger)({
        transports: [
          new (winston.transports.Console)(),
          new (winston.transports.File)({ filename: 'win.log' })
        ]
      });

var http=require('http');

var server = http.createServer(function(request, response){
    response.writeHead(200, {'Content-Type': 'text/plain'});
    var rd = Math.random() * 50;
    logger.info("hello " + rd);
    response.write('hello ');
    if (Math.floor(rd) == 30){
        process.exit(1);
    }
    response.end();
}).listen(4444);

ab testing command

ab -c 10 -n 100 localhost:4444/

console log result all request

$ node winston.js 
info: hello 40.635715366806835
info: hello 47.55378740373999
info: hello 3.97098318208009
info: hello 21.402712271083146
info: hello 13.45938507001847
info: hello 34.73868641303852
info: hello 35.19469986204058
info: hello 17.50683527207002
info: hello 46.6102683218196
info: hello 16.208414710126817
info: hello 18.39921014616266
info: hello 23.423498892225325
info: hello 44.21681684907526
info: hello 35.54235898191109
info: hello 9.904313215520233
info: hello 27.047289244364947
info: hello 32.58601982379332
info: hello 36.48257440654561
info: hello 42.66765915090218
info: hello 9.47293157223612
info: hello 38.31890656147152
info: hello 40.63100240891799
info: hello 26.544194167945534
info: hello 17.846915975678712
info: hello 43.33941290387884
info: hello 26.012209930922836
info: hello 30.679881805554032

But file log only has 3 result:

$ cat win.log 
{"level":"info","message":"hello 40.635715366806835","timestamp":"2013-07-30T03:03:43.441Z"}
{"level":"info","message":"hello 47.55378740373999","timestamp":"2013-07-30T03:03:43.446Z"}
{"level":"info","message":"hello 3.97098318208009","timestamp":"2013-07-30T03:03:43.446Z"}