From 6d6c502084423ebed8eb5573f5208017740fca68 Mon Sep 17 00:00:00 2001
From: diandian <xingdianvip@gmail.com>
Date: Mon, 24 Apr 2023 11:30:28 +0800
Subject: [PATCH] =?UTF-8?q?=E4=B8=8A=E4=BC=A0=E6=96=87=E4=BB=B6=E8=87=B3?=
 =?UTF-8?q?=20'Shell-MD'?=
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+<h1><center>shell并发控制</center></h1>
+
+作者：行癫（盗版必究）
+
+------
+
+## 一：FD文件描述符
+
+#### 1.FD简述
+
+​		FD：文件描述符/文件句柄
+
+​		进程使用文件描述符用来管理进程打开的文件
+
+```shell
+[root@xingdiancloud ~]# ll /proc/$$/fd
+总用量 0
+lrwx------. 1 root root 64  4月 16 23:51 0 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 1 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 2 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 255 -> /dev/pts/0
+[root@xingdiancloud ~]# touch file1
+启用自定义文件描述符打开文件
+[root@xingdiancloud ~]# exec 6<> file1
+[root@xingdiancloud ~]# ll /proc/$$/fd
+总用量 0
+lrwx------. 1 root root 64  4月 16 23:51 0 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 1 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 2 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 255 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 6 -> /root/file1
+[root@xingdiancloud ~]# echo "xingdian" > /proc/$$/fd/6
+[root@xingdiancloud ~]# cat file1
+xingdian
+[root@xingdiancloud ~]# rm -rf file1
+[root@xingdiancloud ~]# ll /proc/$$/fd
+总用量 0
+lrwx------. 1 root root 64  4月 16 23:51 0 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 1 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 2 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 255 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 6 -> '/root/file1 (deleted)'
+[root@xingdiancloud ~]# cat /proc/$$/fd/6
+xingdian
+释放文件描述符
+[root@xingdiancloud ~]# exec 6<&-
+[root@xingdiancloud ~]# ll /proc/$$/fd
+总用量 0
+lrwx------. 1 root root 64  4月 16 23:51 0 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 1 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 2 -> /dev/pts/0
+lrwx------. 1 root root 64  4月 16 23:51 255 -> /dev/pts/0
+```
+
+注意：
+
+​		exec打开一个文件
+
+​		exec关闭一个文件(释放文件句柄)
+
+​		当一个文件FD未被释放，删除源文件也不会影响FD
+
+#### 2.管道简述
+
+匿名管道
+
+```shell
+[root@xingdiancloud ~]# rpm -qa | grep rpm
+```
+
+命令管道
+
+```shell
+[root@xingdiancloud ~]# mkfifo /tmp/xingdian
+[root@xingdiancloud ~]# file /tmp/xingdian
+/tmp/xingdian: fifo (named pipe)
+[root@xingdiancloud ~]# tty
+/dev/pts/0
+[root@xingdiancloud ~]# rpm -qa > /tmp/xingdian
+
+另一个终端
+[root@xingdiancloud ~]# grep bash /tmp/xingdian
+bash-5.1.8-6.el9.x86_64
+bash-completion-2.11-4.el9.noarch
+[root@xingdiancloud ~]# tty
+/dev/pts/1
+```
+
+#### 3.FD案例
+
+```shell
+[root@xingdiancloud ~]# cat a.sh
+#!/bin/bash
+exec 7<> /etc/hosts
+exec 8<> /etc/hostname
+
+while read -u 7 line
+do
+        echo $line
+done
+while read -u 8 line2
+do
+        echo $line2
+done
+exec 7<&-
+exec 8<&-
+
+[root@xingdiancloud ~]# bash a.sh
+127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
+::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
+xingdiancloud
+```
+
+4.并发案例
+
+```shell
+#!/usr/bin/bash
+#固定线程
+read -p "请输入线程数量：" diange
+diangefile=/root/diangefile
+mkfifo $diangefile                //虚拟管道
+exec 8<>$diangefile               //文件描述
+rm -rf $diangefile
+
+for i in `seq $diange`
+do
+        echo  >&8                   //将内容写入到描述文件中,写如了空行
+done
+
+for i in {1..100}
+do
+        read -u 8                   //read 读取描述文件中的内容
+        {
+        ip=192.168.101.$i
+        ping -c1 $ip &>/dev/null
+        if [ $? -eq 0 ];then
+                echo "$ip is up"
+        else
+                echo "$ip is down"
+
+        fi
+        echo >&8                   //等到进程执行完之后再往管道里丢内容以支持后面的循环
+        }&
+done
+wait
+echo "完成"
+exec 8<&-                          //释放描述文件
+```
+
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