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java 实现共享锁和排它锁
一直对多线程有恐惧，在实现共享锁和排它锁之后，感觉好了很多。
共享锁 就是查询的时候，如果没有修改，可以支持多线程查询；
排它锁 就是修改的时候，锁定共享锁，停止查询，同时，锁定排它锁，只允许一个线程进行修改，修改完成后，再解开共享锁；
心路历程： 一开始的想法是，绝对不调用 sleep ，要用到sleep 的地方我觉得都可以用 notify() 和 wait() 替换，sleep（T） 我觉得T 的大小压根是无法算出来的，如果非要用sleep 我觉得T 的时间应该是一个动态的值，这个值是通过函数的执行时间的一个平均值（每N次执行算一个 平均值出来） 但个人觉得还是不如notify() 和wait(); 我为了简单，操作的是一颗字典树代替B树；如何实现读支持多线程，写单线程呢！ 当各种查询和修改的操作以多线程的方式提交给线程池的时候，程序会从阻塞队列里面不断的取任务，当前面取到的任务是 查询的时候，不要管他，没有修改表结构，直接丢给一个线程，当取到的下任务是一个修改或者更新的任务时，首先必须等待前面的查询全部查询完，然后再停掉阻塞队列不断的添加任务， 要让我修改完成之后，再唤醒阻塞队列添加任务；由于我不知道如何停掉线程池的阻塞队列添加任务，所以干脆自己模拟线程池这个过程；（理论上这个方法是可行的） 主要的卡是在notify() 和 wait()的理解上面，这两个方法执行时都必须在 锁里面； 所以在查询的代码里面，你不能wait() 那样会变成单线程；
1 insert; 2 remove; 3 query; -1 stopRun
1 package com.trafree; 2 3 import java.io.File; 4 import java.io.IOException; 5 import java.util.*; 6 import java.util.concurrent.atomic.AtomicInteger; 7 8 /** 9 * Created by on_the_way on 2014/12/31. 10 */ 11 public class AboutThread { 12 13 public static boolean insert(String str) { 14 int len = str.length(); 15 Trie p = root; 16 for (int i = 0; i < len; i++) { 17 int num = str.charAt(i) - ‘a‘; 18 if (p.next[num] == null) { 19 p.next[num] = new Trie(); 20 } 21 p = p.next[num]; 22 } 23 if (p.end) return false; 24 return p.end = true; 25 } 26 27 public static boolean remove(String str) { 28 int len = str.length(); 29 Trie p = root; 30 for (int i = 0; i < len; i++) { 31 int num = str.charAt(i) - ‘a‘; 32 if (p.next[num] == null) { 33 return false; 34 } 35 p = p.next[num]; 36 } 37 if (!p.end) { 38 return false; 39 } 40 p.end = false; 41 return true; 42 } 43 44 public static boolean query(String str) { 45 int len = str.length(); 46 Trie p = root; 47 for (int i = 0; i < len; i++) { 48 int num = str.charAt(i) - ‘a‘; 49 if (p.next[num] == null) { 50 return false; 51 } 52 p = p.next[num]; 53 } 54 return p.end; 55 } 56 57 public static Trie root = new Trie(); 58 59 public static class Trie { 60 public Trie next[] = new Trie[26]; 61 public boolean end; 62 63 public Trie() { 64 for (int i = 0; i < 26; i++) { 65 this.next[i] = null; 66 } 67 this.end = false; 68 } 69 } 70 71 public static class Consumer implements Runnable { 72 public void run() { 73 try { 74 MyThread.process(); 75 } catch (Exception e) { 76 e.printStackTrace(); 77 } 78 } 79 } 80 81 public static class MyThread implements Runnable { 82 83 public int sequence; 84 public int action; 85 public String str; 86 public boolean res; 87 88 public static Object lock1 = new Object(); 89 public static Object lock2 = new Object(); 90 public static Object lock3 = new Object(); 91 92 public static boolean needNotify1 = false; 93 public static boolean needNotify2 = false; 94 public static boolean needNotify3 = false; 95 public static boolean runModify = false; 96 97 public static AtomicInteger queryNum = new AtomicInteger(0); 98 public static Queue<MyThread> pool = new LinkedList<MyThread>(); 99 100 public MyThread(int sequence, int action, String str) {101 this.sequence = sequence;102 this.action = action;103 this.str = str;104 this.res = false;105 }106 107 public static void process() throws InterruptedException {108 109 boolean needBreak = false;110 while (true) {111 if( pool.size() == 0 && needBreak ){112 break;113 }114 synchronized (lock1) {115 if (pool.size() == 0) {116 needNotify1 = true;117 lock1.wait();118 }119 }120 synchronized (lock3) {121 if (runModify) {122 needNotify3 = true;123 lock3.wait();124 }125 }126 MyThread myThread = pool.poll();127 128 if (myThread.action == -1){129 needBreak = true;continue;130 }131 if (myThread.action == 1 || myThread.action == 2) {132 synchronized (lock2) {133 if (queryNum.get() != 0) {134 needNotify2 = true;135 runModify = true;136 lock2.wait();137 new Thread(myThread).start();138 } else {139 runModify = true;140 new Thread(myThread).start();141 }142 }143 } else {144 queryNum.incrementAndGet();145 new Thread(myThread).start();146 }147 }148 }149 150 public void run() {151 if (this.action == 1) {152 this.res = insert(this.str);153 synchronized (lock3) {154 needNotify1 = false;155 runModify = false;156 if( needNotify3 )lock3.notify();157 }158 System.out.println(sequence+" "+action+" "+str+" "+res);159 } else if (this.action == 2) {160 this.res = remove(this.str);161 synchronized (lock3) {162 needNotify1 = false;163 runModify = false;164 if( needNotify3 )lock3.notify();165 }166 System.out.println(sequence+" "+action+" " + str+" "+res);167 } else {168 this.res = query(str);169 System.out.println(sequence+" "+action+" "+str+" "+res);170 synchronized (lock2) {171 if (queryNum.decrementAndGet() == 0 ) {172 if(needNotify2)lock2.notify();173 }174 }175 }176 }177 178 }179 180 public static void main(String arg[]) throws IOException {181 182 File file = new File("F:" + File.separator + "in.txt");183 Scanner cin = new Scanner(file);184 int N = cin.nextInt();185 int M = cin.nextInt();186 187 for (int i = 0; i < N; i++) {188 insert(cin.next());189 }190 191 new Thread(new Consumer()).start();192 for (int i = 0; i < M; i++) {193 MyThread myThread = new MyThread(i, cin.nextInt(), cin.next());194 synchronized (MyThread.lock1) {195 MyThread.pool.add(myThread);196 if (MyThread.needNotify1) {197 MyThread.needNotify1 = false;198 MyThread.lock1.notify();199 }200 }201 }202 }203 }
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java 实现共享锁和排它锁