Python 理解TCP侦听积压

我打算深入了解更改TCP连接队列大小的影响。因此，我编写了一个简单的服务器/客户端对来测试它

服务器在python模块

SocketServer

中实例化

forkingcserver

。为了测试挂起连接队列大小的影响，我覆盖服务器的两个参数，如下所示：

max_children = 1        # default 40, max number of child processes
request_queue_size = 0  # default 5, socket listen() backlog

下面是服务器的请求处理程序，它提供了一个简单的“延迟”回显服务

class RequestHandler(socketserver.StreamRequestHandler):
    def handle(self):
        self.data = self.rfile.readline().strip()
        time.sleep(30)
        self.wfile.write(self.data)

在客户机中，10个套接字连接服务器并同时发送一条线路

for i in xrange(10): 
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sockets.append(s)
    s.connect_ex(address)
    s.sendall('{}\n'.format(i)

结果只有3-4个插座成功连接。其他人甚至没有完成三方握手，最后服务器向他们发送了一个

RST

。下面是一个失败客户端的tcpdump输出。可以看出，服务器（端口：10086）从客户端（端口：53241）接收到

SYN

，并发回

SYN/ACK

。客户端在收到

SYN/ACK

时也发送了

ACK

。但是，服务器似乎没有从客户端接收到

ACK

。因此，它一直向客户端发送

SYN/ACK

，最后通过发送

RST

放弃

有人能解释一下为什么服务器没有看到

ACK

？是因为连接队列溢出吗

17:41:30.568077 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [S], seq 3931554775, win 32792, options [mss 16396,sackOK,TS val 2434238 ecr 0,nop,wscale 6], length 0
17:41:30.568090 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2434238 ecr 2434238,nop,wscale 6], length 0
17:41:30.568100 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2434238 ecr 2434238], length 0
17:41:30.568479 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2434239 ecr 2434238], length 2
17:41:30.770902 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2434440 ecr 2434238], length 2
17:41:31.172453 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2434843 ecr 2434238], length 2
17:41:31.767360 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2435438 ecr 2434843,nop,wscale 6], length 0
17:41:31.767391 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2435438 ecr 2434238], length 0
17:41:31.976349 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2435647 ecr 2434238], length 2
17:41:33.584352 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2437255 ecr 2434238], length 2
17:41:33.969825 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2437640 ecr 2437255,nop,wscale 6], length 0
17:41:33.969854 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2437640 ecr 2434238], length 0
17:41:36.800489 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2440471 ecr 2434238], length 2
17:41:38.177461 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2441848 ecr 2440471,nop,wscale 6], length 0
17:41:38.177493 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2441848 ecr 2434238], length 0
17:41:43.232468 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2446903 ecr 2434238], length 2
17:41:46.193321 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2449864 ecr 2446903,nop,wscale 6], length 0
17:41:46.193352 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2449864 ecr 2434238], length 0
17:41:56.096467 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2459767 ecr 2434238], length 2
17:42:02.211676 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2465882 ecr 2459767,nop,wscale 6], length 0
17:42:02.211698 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2465882 ecr 2434238], length 0
17:42:21.825117 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2485495 ecr 2434238], length 2
17:43:13.281525 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2536952 ecr 2434238], length 2
17:43:13.281625 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [R], seq 2946632839, win 0, length 0

是因为连接队列溢出吗

17:41:30.568077 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [S], seq 3931554775, win 32792, options [mss 16396,sackOK,TS val 2434238 ecr 0,nop,wscale 6], length 0
17:41:30.568090 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2434238 ecr 2434238,nop,wscale 6], length 0
17:41:30.568100 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2434238 ecr 2434238], length 0
17:41:30.568479 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2434239 ecr 2434238], length 2
17:41:30.770902 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2434440 ecr 2434238], length 2
17:41:31.172453 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2434843 ecr 2434238], length 2
17:41:31.767360 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2435438 ecr 2434843,nop,wscale 6], length 0
17:41:31.767391 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2435438 ecr 2434238], length 0
17:41:31.976349 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2435647 ecr 2434238], length 2
17:41:33.584352 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2437255 ecr 2434238], length 2
17:41:33.969825 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2437640 ecr 2437255,nop,wscale 6], length 0
17:41:33.969854 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2437640 ecr 2434238], length 0
17:41:36.800489 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2440471 ecr 2434238], length 2
17:41:38.177461 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2441848 ecr 2440471,nop,wscale 6], length 0
17:41:38.177493 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2441848 ecr 2434238], length 0
17:41:43.232468 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2446903 ecr 2434238], length 2
17:41:46.193321 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2449864 ecr 2446903,nop,wscale 6], length 0
17:41:46.193352 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2449864 ecr 2434238], length 0
17:41:56.096467 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2459767 ecr 2434238], length 2
17:42:02.211676 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [S.], seq 2946632838, ack 3931554776, win 32768, options [mss 16396,sackOK,TS val 2465882 ecr 2459767,nop,wscale 6], length 0
17:42:02.211698 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [.], ack 1, win 513, options [nop,nop,TS val 2465882 ecr 2434238], length 0
17:42:21.825117 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2485495 ecr 2434238], length 2
17:43:13.281525 IP localhost.localdomain.53241 > localhost.localdomain.10086: Flags [P.], seq 1:3, ack 1, win 513, options [nop,nop,TS val 2536952 ecr 2434238], length 2
17:43:13.281625 IP localhost.localdomain.10086 > localhost.localdomain.53241: Flags [R], seq 2946632839, win 0, length 0

---

否。如果待办事项队列已满，它将不会发送SYN/ACK，它将不执行任何操作或发送RST，具体取决于平台。

此问题的答案将高度依赖于平台。您使用的操作系统和操作系统版本是什么？