我的理解synchronized就是將線程可能擾亂的程序塊包裹起來,使synchronized塊中的程序不至於被分開執行,而是作爲一個元操作。
看段示例:
public class Synch implements Runnable {
public static void main(String args[]) {
Synch mt = new Synch();
Thread t1 = new Thread(mt, "t1");
Thread t2 = new Thread(mt, "t2");
Thread t3 = new Thread(mt, "t3");
Thread t4 = new Thread(mt, "t4");
Thread t5 = new Thread(mt, "t5");
Thread t6 = new Thread(mt, "t6");
Thread t7 = new Thread(mt, "t7");
Thread t8 = new Thread(mt, "t8");
Thread t9 = new Thread(mt, "t9");
Thread t0 = new Thread(mt, "t0");
t1.start();
t2.start();
t3.start();
t4.start();
t5.start();
t6.start();
t7.start();
t8.start();
t9.start();
t0.start();
}
public void run() {
synchronized (this) {
System.out.println("_____");
System.out.println("F: " + Thread.currentThread().getName());
System.out.println("A: " + Thread.currentThread().getName());
}
}
}
運行結果(某次,不確定):
_____
F: t1
A: t1
_____
F: t3
A: t3
_____
F: t5
A: t5
_____
F: t2
A: t2
_____
F: t7
A: t7
_____
F: t4
A: t4
_____
F: t6
A: t6
_____
F: t8
A: t8
_____
F: t9
A: t9
_____
F: t0
A: t0
雖然數字基本無序,但是F:A:輸出有序
將synchronized段註釋掉,再看輸出結果:
_____
F: t1
A: t1
_____
F: t3
_____
F: t2
A: t2
A: t3
_____
F: t9
A: t9
_____
F: t4
A: t4
_____
_____
_____
F: t6
A: t6
_____
F: t7
F: t8
A: t8
A: t7
F: t5
_____
F: t0
A: t0
A: t5
輸出可以說是亂七八糟,線程的運行順序完全沒法控制。