[Android study notes] JAVA basics - multi-threaded data security

Multi-threaded data security: ensuring data integrity Methods for
synchronizing threads

class MyThread implements Runnable{
	int i=100;
	
	public void run(){//Rewrite the run method
		while(true)
		{
			//Print the name of the current thread and the value of the i variable
			System.out.println(Thread.currentThread().getName() + i);
			i--;
			Thread.yield();
			if(i<0) break;
		}
	}
}

class Test{
	public static void main(String args[])
	{
		MyThread myThread = new MyThread;
		
		//Generate two Thread objects, but these two objects share a thread body
		Thread t1 = new Thread(myThread);
		Thread t2 = new Thread(myThread);
		//Each thread has a name, you can set the name of the thread through the setName() of the Thread object
		//You can also use the getName method to get the name of the thread
		t1.setName("Thread A");
		t2.setName("Thread B");
		
		// start two threads separately
		t1.start();
		t2.start();
	}
}

The running result is as follows

Thread-->B11
Thread-->A10
Thread-->B9
Thread-->A8
Thread-->B7
Thread-->A5
Thread-->B5
Thread-->A4
Thread-->B3
Thread-->A2
Thread-->B1
Thread-->A0

It is found that data is lost and repeated errors. This is the error that occurs when multiple threads share the same data. At this time, thread synchronization is required.
Modified sync code

public void run(){
	while(true)
	{
		/* use synchronized code blocks */
		synchronized(this){
		System.out.println(Thread.currentThread().getName() + i);
		i--;
		Thread.yield();/*让出CPU*/
		if(i<0) break;
		}
	}
}

When synchronized is used, once a thread acquires the synchronization lock of an object, all the synchronized code on the object will be locked and cannot be used by other threads.
In addition to the synchronization code block, synchronized can also be used to synchronize methods, functions is similar, such as:

public synchronized void fun()
{
	
}

By Urien April 14, 2018 14:02:27