#! /usr/bin/python2.4
import errno
import os
import select
import socket
import sys
import time

def NonBlockingConnect(sock,addr):
  #time.sleep(0.0001)  # Fixes the problem.
  while True:
    try:
      return sock.connect(addr)
    except socket.error,e:
      if e.args[0] not in (errno.EINPROGRESS,errno.EALREADY):
        raise
      os.write(2,'^')
      if not select.select((),(sock,),(),0.5)[1]:
        os.write(2,'P')

def InfiniteClient(addr):
  while True:
    sock = socket.socket(socket.AF_INET,socket.SOCK_STREAM,0)
    sock.setblocking(0)
    sock.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
    # sock.connect(addr)
    NonBlockingConnect(sock,addr)
    sock.close()
    os.write(2,'.')

def InfiniteServer(server_socket):
  while True:
    sock,addr = server_socket.accept()
    sock.close()

server_socket = socket.socket(socket.AF_INET,0)
server_socket.setsockopt(socket.SOL_SOCKET,1)
server_socket.bind(('127.0.0.1',45454))
server_socket.listen(128)

if os.fork():  # Parent.
  InfiniteServer(server_socket)
else:
  addr = server_socket.getsockname()
  server_socket.close()
  InfiniteClient(addr)

使用NonBlockingConnect,大多数connect()操作都很快,但是每隔几秒就会发生一次connect()操作,至少需要2秒(由输出上的5个连续P字母表示).通过使用sock.connect而不是NonBlockingConnect,所有连接操作似乎都很快.

怎么可能摆脱这些慢连接()？

我正在使用标准PAE内核运行Ubuntu Karmic桌面：

Linux narancs 2.6.31-20-generic-pae #57-Ubuntu SMP Mon Feb 8 10:23:59 UTC 2010 i686 GNU/Linux

奇怪的是strace -f ./conn.py没有延迟.

奇怪的是,如果我取消注释非常快的时间,就没有延迟.sleep.

奇怪的是,我的Ubuntu Hardy系统没有延迟：

所有这些系统都受到影响(运行Ubuntu Karmic,Ubuntu Hardy,Debian Etch)：

Linux narancs 2.6.31-20-generic-pae #57-Ubuntu SMP Mon Feb 8 10:23:59 UTC 2010 i686 GNU/Linux
Linux t 2.6.24-grsec #1 SMP Thu Apr 24 14:15:58 CEST 2008 x86_64 GNU/Linux
Linux geekpad 2.6.24-24-generic #1 SMP Fri Sep 18 16:49:39 UTC 2009 i686 GNU/Linux

奇怪的是,以下Debian Lenny系统不受影响：

Linux t 2.6.31.5 #2 SMP Thu Nov 5 15:33:05 CET 2009 i686 GNU/Linux

仅供参考我使用AF_UNIX插槽时没有延迟.

仅供参考我如果在C中实现客户端,我会得到相同的行为：

/* by pts@fazekas.hu at Sun Apr 25 20:47:24 CEST 2010 */
#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <unistd.h>

static int work(void) {
  fd_set rset;
  fd_set wset;
  fd_set eset;
  socklen_t sl; 
  struct timeval timeout;
  struct sockaddr_in sa;
  int sd,i,j;
  long l;
  sd = socket(AF_INET,SOCK_STREAM,0);
  if (sd < 0) {
    perror("socket");
    return 2;
  }
  l = fcntl(sd,F_GETFL,0);
  if (l < 0) {
    perror("fcntl-getfl");
    close(sd);
    return 2;
  }
  if (0 != fcntl(sd,F_SETFL,l | O_NONBLOCK)) {
    perror("fcntl-setfl");
    close(sd);
    return 2;
  }
  memset(&sa,'\0',sizeof(sa));
  sa.sin_family = AF_INET;
  sa.sin_port = htons(45454);
  sa.sin_addr.s_addr = inet_addr("127.0.0.1");
  while (0 != connect(sd,(struct sockaddr*)&sa,sizeof sa)) {
    if (errno != EAGAIN && errno != EINPROGRESS && errno != EALREADY) {
      perror("connect");
      close(sd);
      return 2;
    }
    FD_ZERO(&rset);
    FD_ZERO(&wset);
    FD_ZERO(&eset);

    j = 0;
    do {
      timeout.tv_sec = 0;
      timeout.tv_usec = 100 * 1000;  /* 0.1 sec */
      FD_SET(sd,&wset);
      FD_SET(sd,&eset);
      i = select(sd + 1,&rset,&wset,&eset,&timeout);
      if (i < 0) {
        perror("select");
        close(sd);
        return 2;
      }  
      if (++j == 5) {
        (void)write(2,"P",1);
        j = 0;
      }
    } while (i == 0);
    sl = sizeof i;
    if (0 != getsockopt(sd,SOL_SOCKET,SO_ERROR,&i,&sl)) {
      perror("getsockopt");
      close(sd);
      return 2;
    }
    if (i != 0) {
      if (i == ECONNRESET) {
        (void)write(2,"R",1);
        close(sd);
        return -3;
      }
      fprintf(stderr,"connect-SO_ERROR: %s\n",strerror(i));
      close(sd);
      return 2;
    }
  }
  close(sd);
  return 0;
}

int main(int argc,char**argv) {
  int i;
  (void)argc;
  (void)argv;
  while ((i = work()) <= 0) (void)write(2,".",1);
  return i;
}