使用runnable實現數據共享，供大家參考，具體內容如下
先上代碼：
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public class testthread { private static final logger logger = loggerfactory.getlogger(testthread.class); private final class myrunnable implements runnable { private int i; public myrunnable() { this.i = 10; } public void run() { while(i > 0) { synchronized (this) { if (i > 0) { i--; logger.debug("{} buy one ticket, {} left. ", thread.currentthread().getname(), i); } } } } } @test public void testrunable() throws interruptedexception{ myrunnable myrunnable = new myrunnable(); thread th1 = new thread(myrunnable); thread th2 = new thread(myrunnable); th1.start(); th2.start(); th1.join(); th2.join(); }} |
樓上的代碼很簡單，模擬一個售票系統。通過兩個thread對象開啟兩條線程同時運行一個myrunnable實例。
幾個注意點：
1. 沒有加上synchronised關鍵詞的話，即
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public void run() { while(i > 0) { if (i > 0) { i--; logger.debug("{} buy one ticket, {} left. ", thread.currentthread().getname(), i); } } } |
系統的運行結果：
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thread-1 buy one ticket, 8 left. thread-2 buy one ticket, 8 left. thread-2 buy one ticket, 6 left. thread-1 buy one ticket, 6 left. thread-2 buy one ticket, 5 left. thread-1 buy one ticket, 4 left. thread-2 buy one ticket, 3 left. thread-1 buy one ticket, 2 left. thread-2 buy one ticket, 1 left. thread-1 buy one ticket, 0 left. |
可以看到，缺少同步的程序輸出明顯有問題。
2. 在進入同步代碼塊之后，還需要對i的值再進行一次判斷，即，如果不加if判斷：
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public void run() { while(i > 0) { synchronized (this) { i--; logger.debug("{} buy one ticket, {} left. ", thread.currentthread().getname(), i); } } } |
程序的運行結果為：
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thread-2 buy one ticket, 9 left. thread-2 buy one ticket, 8 left. thread-2 buy one ticket, 7 left. thread-2 buy one ticket, 6 left. thread-2 buy one ticket, 5 left. thread-2 buy one ticket, 4 left. thread-2 buy one ticket, 3 left. thread-2 buy one ticket, 2 left. thread-2 buy one ticket, 1 left. thread-2 buy one ticket, 0 left. thread-1 buy one ticket, -1 left. |
可以看出，出現了“多賣”的現象， 所以需要在進入同步代碼塊中再進行一次if判斷。
總結
synchronised用于互斥訪問共享變量， 并在同步代碼塊中使用if判斷更新共享變量。
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持服務器之家。
原文鏈接：https://blog.csdn.net/NewUser2771894007/article/details/79630721
