JAVA并发编程的挑战

public class ConcurrencyTest {
	/** 执行次数 */
	private static final long count = 40000l;

	public static void main(String[] args) throws InterruptedException {
		// 并发计算
		concurrency();
		// 单线程计算
		serial();
	}

	private static void concurrency() throws InterruptedException {
		long start = System.currentTimeMillis();
		Thread thread = new Thread(new Runnable() {
			@Override
			public void run() {
				int a = 0;
				for (long i = 0; i < count; i++) {
					a += 5;
				}
				System.out.println(a);
			}
		});
		thread.start();
		int b = 0;
		for (long i = 0; i < count; i++) {
			b--;
		}
		long time = System.currentTimeMillis() - start;
		thread.join();
		System.out.println("concurrency: " + time + "ms,b=" + b);
	}

	private static void serial() {
		long start = System.currentTimeMillis();
		int a = 0;
		for (long i = 0; i < count; i++) {
			a += 5;
		}
		int b = 0;
		for (long i = 0; i < count; i++) {
			b--;
		}
		long time = System.currentTimeMillis() - start;
		System.out.println("serial:" + time + "ms,b=" + b + ",a=" + a);

	}
}


//测试结果
循环次数	串行执行耗时（单位ms）	并发执行耗时	并发比串行快多少
1亿			130						77			约1倍
1千万			18						9		   约1倍
1百万			5						5		   差不多
10万			 4						 3			慢
1万			 0						 1			慢

public class DeadLockDemo {
	/** A锁 */
	private static String A = "A";

	/** B锁 */
	private static String B = "B";

	public static void main(String[] args) {
		new DeadLockDemo().deadLock();
	}

	private void deadLock() {
		Thread t1 = new Thread(new Runnable() {
			@Override
			public void run() {
				synchronized (A) {
					try {
						Thread.sleep(2000);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					synchronized (B) {
						System.out.println("1");
					}
				}
			}
		});

		Thread t2 = new Thread(new Runnable() {
			@Override
			public void run() {
				synchronized (B) {
					synchronized (A) {
						System.out.println("2");
					}
				}
			}
		});
		t1.start();
		t2.start();
	}
}

> jps
88230 DeadLockDemo
71787 
88236 Jps

> jstack 88230
"Thread-1" #11 prio=5 os_prio=31 tid=0x00007fc230867800 nid=0x5903 waiting for monitor entry [0x000070000c152000]
   java.lang.Thread.State: BLOCKED (on object monitor)
	at DeadLockDemo$2.run(DeadLockDemo.java:36)
	- waiting to lock <0x00000007aab729f0> (a java.lang.String)
	- locked <0x00000007aab72a20> (a java.lang.String)
	at java.lang.Thread.run(Thread.java:748)

"Thread-0" #10 prio=5 os_prio=31 tid=0x00007fc230866800 nid=0x5703 waiting for monitor entry [0x000070000c04f000]
   java.lang.Thread.State: BLOCKED (on object monitor)
	at DeadLockDemo$1.run(DeadLockDemo.java:25)
	- waiting to lock <0x00000007aab72a20> (a java.lang.String)
	- locked <0x00000007aab729f0> (a java.lang.String)
	at java.lang.Thread.run(Thread.java:748)
     

Found one Java-level deadlock:
=============================
"Thread-1":
  waiting to lock monitor 0x00007fc2318268b8 (object 0x00000007aab729f0, a java.lang.String),
  which is held by "Thread-0"
"Thread-0":
  waiting to lock monitor 0x00007fc231827d58 (object 0x00000007aab72a20, a java.lang.String),
  which is held by "Thread-1"

Java stack information for the threads listed above:
===================================================
"Thread-1":
	at DeadLockDemo$2.run(DeadLockDemo.java:36)
	- waiting to lock <0x00000007aab729f0> (a java.lang.String)
	- locked <0x00000007aab72a20> (a java.lang.String)
	at java.lang.Thread.run(Thread.java:748)
"Thread-0":
	at DeadLockDemo$1.run(DeadLockDemo.java:25)
	- waiting to lock <0x00000007aab72a20> (a java.lang.String)
	- locked <0x00000007aab729f0> (a java.lang.String)
	at java.lang.Thread.run(Thread.java:748)

Found 1 deadlock.