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使用Runnable實(shí)現(xiàn)數(shù)據(jù)共享,供大家參考,具體內(nèi)容如下
先上代碼:
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 th2 = new Thread(myRunnable); Thread th3 = new Thread(myRunnable); th2.start(); th3.start(); th2.join(); th3.join(); } }
樓上的代碼很簡單,模擬一個(gè)售票系統(tǒng)。通過兩個(gè)Thread對(duì)象開啟兩條線程同時(shí)運(yùn)行一個(gè)MyRunnable實(shí)例。
幾個(gè)注意點(diǎn):
1. 沒有加上synchronised關(guān)鍵詞的話,即
public void run() { while(i > 0) { if (i > 0) { i--; logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i); } } }
系統(tǒng)的運(yùn)行結(jié)果:
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(jìn)入同步代碼塊之后,還需要對(duì)i的值再進(jìn)行一次判斷,即,如果不加if判斷:
public void run() { while(i > 0) { synchronized (this) { i--; logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i); } } }
程序的運(yùn)行結(jié)果為:
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(xiàn)了“多賣”的現(xiàn)象, 所以需要在進(jìn)入同步代碼塊中再進(jìn)行一次if判斷。
總結(jié)
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(nèi)容,希望對(duì)大家的學(xué)習(xí)有所幫助,也希望大家多多支持億速云。
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