爲什麼Socket.connect失敗嘗試在Windows上需要1秒？

Question

使用.net，我注意到試圖連接到一個未被偵聽的端口總是需要1秒鐘。要檢查這是否是在.NET抽象或者它是否是一個較低的水平問題了問題，並把它與Linux（其中一個不成功telnet需要像爲3ms）比較，我用的node.js腳本連接到端口

• 12345，端口無進程
• 80聽，上正在

結果聽了的Windows端口：

Connecting to 127.0.0.1:12345 
#3: error elapsed: 1000ms, Error: connect ECONNREFUSED 
#2: error elapsed: 1002ms, Error: connect ECONNREFUSED 
#4: error elapsed: 1003ms, Error: connect ECONNREFUSED 
#1: error elapsed: 1007ms, Error: connect ECONNREFUSED 
#0: error elapsed: 1015ms, Error: connect ECONNREFUSED 

Connecting to 127.0.0.1:80 
#0: connect elapsed: 8ms 
#1: connect elapsed: 1ms 
#2: connect elapsed: 3ms 
#3: connect elapsed: 4ms 
#4: connect elapsed: 6ms 

個

結果Linux的：

Connecting to 127.0.0.1:12345 
#4: error elapsed: 0ms, Error: connect ECONNREFUSED 
#3: error elapsed: 1ms, Error: connect ECONNREFUSED 
#2: error elapsed: 1ms, Error: connect ECONNREFUSED 
#1: error elapsed: 1ms, Error: connect ECONNREFUSED 
#0: error elapsed: 3ms, Error: connect ECONNREFUSED 

Connecting to 127.0.0.1:80 
#4: connect elapsed: 0ms 
#3: connect elapsed: 0ms 
#2: connect elapsed: 0ms 
#1: connect elapsed: 1ms 
#0: connect elapsed: 2ms 

Node.js的源：

var net = require('net'); 
var host = process.argv[2]; 
var port = Number(process.argv[3]); 
console.log("Connecting to %s:%d", host, port); 
for (i = 0; i < 5; i++) 
{ 
    (function(i) { 
    var date = +new Date; 
    var client = net.connect({host: host, port: port}); 
    client.on('error', function(msg) 
    { 
     console.log("#%d: error elapsed: %dms, %s", i, new Date - date, msg); 
    }); 
    client.on('connect', function() 
    { 
     console.log("#%d: connect elapsed: %dms", i, new Date - date); 
    }); 
    })(i); 
} 

有兩點要注意

• 我也試過遠程IP地址，結果是與上面顯示的localhost相似
• 在node.js和我寫它的方式中，（異步）連接嘗試並行運行，但在.net的情況下，我正在同步測試，即一個嘗試在另一個之後，結果是相同的：1秒每次

任何想法，爲什麼視窗是慢嗎？這是一種有意的節流？

Answer 1

@ HarryJohnston的評論使我改寫程序，看看

如果其他程序啓動監聽該端口的那一秒的延遲

期間它似乎會發生什麼，在Windows上， connect（）調用嘗試以500ms爲間隔連接到未綁定端口最多3次。如果第三次嘗試也失敗了，它就放棄了。

這裏有一個試運行，在那裏我偶爾無規開始和停止的12345端口上偵聽過程的日誌：

Connecting to 192.168.77.11:12345 
#1: error elapsed: 1008ms, Error: connect ECONNREFUSED 
#2: error elapsed: 1001ms, Error: connect ECONNREFUSED 
#3: error elapsed: 1004ms, Error: connect ECONNREFUSED 
#4: connect elapsed: 1001ms 
#5: connect elapsed: 1000ms 
#6: connect elapsed: 500ms 
#7: error elapsed: 1000ms, Error: connect ECONNREFUSED 
#8: connect elapsed: 1001ms 
#9: error elapsed: 1000ms, Error: connect ECONNREFUSED 
#10: connect elapsed: 500ms 
#11: error elapsed: 1000ms, Error: connect ECONNREFUSED 
#12: error elapsed: 1000ms, Error: connect ECONNREFUSED 
#13: connect elapsed: 500ms 
#14: error elapsed: 1000ms, Error: connect ECONNREFUSED 
#15: connect elapsed: 500ms 
#16: error elapsed: 1000ms, Error: connect ECONNREFUSED 
#17: connect elapsed: 500ms 
#18: connect elapsed: 1000ms 
#19: connect elapsed: 1000ms 
#20: connect elapsed: 500ms 
#21: connect elapsed: 1011ms 
#22: connect elapsed: 1000ms 
#23: error elapsed: 1000ms, Error: connect ECONNREFUSED 

而修改後的源代碼：

var net = require('net'); 
var host = process.argv[2]; 
var port = Number(process.argv[3]); 
console.log("Connecting to %s:%d", host, port); 
var connect = function(i) { 
    var date = +new Date; 
    var client = net.connect({host: host, port: port}); 
    client.on('error', function(msg) 
    { 
     console.log("#%d: error elapsed: %dms, %s", i, new Date - date, msg); 
     connect(i + 1); 
    }); 
    client.on('connect', function() 
    { 
     console.log("#%d: connect elapsed: %dms", i, new Date - date); 
     connect(i + 1); 
    }); 
    }; 
connect(1);