Java lock & condition-优快云博客

本文深入探讨了Java中Lock与Condition接口的应用，通过示例代码详细解释了ReentrantLock的使用方法，包括读写锁的实现及其在并发场景下的优势。

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java Lock & Condition, provide a similar, yet more extensive locking mechanism than synchronized,

Lock:

similar to the monitor lock used by synchronized, but more powerfull,

Condition:

bound to lock, provide methods similar to wait()/notify()/notifyAll() of Object,

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class & interface

* Lock

interface of lock,

* ReentrantLock

basic implementation of Lock

* Condition

interface of condition,

* ReadWriteLock

interface, read/write version of Lock,

* ReentrantReadWriteLock

basic implementation of ReadWriteLock,

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code

lock test:

package eric.j2se.concurrence.lockcondition;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Lock test
 * 
 * @author eric
 * @date Aug 14, 2012 8:04:57 PM
 */
public class LockTest {
	private static int i;
	private static Lock lk = new ReentrantLock();

	public static void test() {
		List<Thread> list = new ArrayList<Thread>();
		int tcount = 3;
		// prepare threads
		for (int i = 0; i < tcount; i++) {
			list.add(new Thread(new TmpRunnable(), "t-" + i));
		}
		// start threads
		for (int i = 0; i < tcount; i++) {
			list.get(i).start();
		}
	}

	private static class TmpRunnable implements Runnable {
		@Override
		public void run() {
			lk.lock();
			try {
				printTime("begin");
				Thread.sleep(1000 * 1); // sleep a while, for test purpose
				printTime("end");
			} catch (InterruptedException e) {
				e.printStackTrace();
			} finally {
				lk.unlock();
			}
		}
	}

	public static void printTime() {
		printTime("");
	}

	/**
	 * print thread name & time
	 * 
	 * @param info
	 *            additional info to print
	 */
	public synchronized static void printTime(String info) {
		System.out.printf("%s:\t%d,\t,%d,\t%s\n", Thread.currentThread().getName(), ++i, System.currentTimeMillis() / 1000, info);
	}

	public static void main(String[] args) {
		test();
	}
}

condition test:

package eric.j2se.concurrence.lockcondition;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Condition test
 * 
 * @author eric
 * @date Aug 14, 2012 9:10:44 PM
 */
public class ConditionTest {
	private static int i;
	private static int bufSize = 26, size;
	private static char cStart = 97;
	private static char[] cbuf = new char[bufSize];

	private static Lock lk = new ReentrantLock();
	private static Condition cdEmpty = lk.newCondition();
	private static Condition cdFull = lk.newCondition();

	private static final int testInterval = 500; // interval of each step in milliseconds, for test

	/**
	 * fill buffer, start when buffer is empty
	 * 
	 * @throws InterruptedException
	 */
	public static void fill() throws InterruptedException {
		lk.lock();
		try {
			while (size == bufSize) { // buffer is full, wait for condition empty
				cdEmpty.await();
			}

			System.out.printf("\n\n------\nstart fill\n\n");
			while (size < bufSize) { // buffer is not full now, fill it
				char c = (char) (cStart + size);
				cbuf[size++] = c;
				printTime("put: " + new Character(c));
				Thread.sleep(testInterval);
			}
			cdFull.signal(); // buffer is full filled now, need to be read
			System.out.printf("\nbuffer full\n------\n\n");
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			lk.unlock();
		}
	}

	/**
	 * take from buffer & empty it, start when buffer is full
	 * 
	 * @throws InterruptedException
	 */
	public static void take() throws InterruptedException {
		lk.lock();
		try {
			while (size != bufSize) { // not full, wait for condition full
				cdFull.await();
			}
			System.out.printf("\n\n------\nstart take\n\n");
			for (int i = 0; i < bufSize; i++) { // now is full, take
				printTime("take: " + new Character(cbuf[i]));
				size--;
				Thread.sleep(testInterval);
			}
			cdEmpty.signal(); // buffer is empty now, need to be fill
			System.out.printf("\nbuffer empty\n------\n\n");
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			lk.unlock();
		}
	}

	public static void test() {
		// thread to fill buffer
		Thread tFill = new Thread(new Runnable() {
			@Override
			public void run() {
				try {
					while (true)
						fill();
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		}, "t-fill");

		// thread to take from buffer
		Thread tTake = new Thread(new Runnable() {
			@Override
			public void run() {
				try {
					while (true)
						take();
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		}, "t-take");
		tTake.start();
		tFill.start();
	}

	public static void printTime() {
		printTime("");
	}

	/**
	 * print thread name & time
	 * 
	 * @param info
	 *            additional info to print
	 */
	public synchronized static void printTime(String info) {
		System.out.printf("%s:\t%d,\t,%d,\t%s\n", Thread.currentThread().getName(), ++i, System.currentTimeMillis() / 1000, info);
	}

	public static void main(String[] args) {
		test();
	}
}

read/write lock test:

package eric.j2se.concurrence.lockcondition;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * Read Write Lock test
 * 
 * @author eric
 * @date Aug 14, 2012 10:34:08 PM
 */
public class ReadWriteLockTest {
	private static int i;

	private static ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
	private static Lock rlk = lock.readLock();
	private static Lock wlk = lock.writeLock();

	private static String data = "";

	private static volatile long lastUpdate; // track last publish date

	/**
	 * publish data, use write lock,
	 * 
	 * @param newData
	 */
	public static void publish(String newData) {
		wlk.lock();
		try {
			printTime("begin publish");
			data = newData;
			lastUpdate = System.currentTimeMillis(); // modify last update date
			printTime("data:\n\t" + data);
			printTime("end publish");
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			wlk.unlock();
		}
	}

	/**
	 * view data, use read lock
	 * 
	 * @param previousView
	 *            last viewed publish date
	 * @return date of new publish, or -1 if no new publish
	 */
	public static long view(long previousView) {
		if (previousView < lastUpdate) { // new publish
			rlk.lock();
			try {
				printTime("view data:\n\t" + data);
			} catch (Exception e) {
				e.printStackTrace();
			} finally {
				rlk.unlock();
			}
			return lastUpdate;
		} else { // no new publish
			printTime("no new publish yet");
			return -1;
		}
	}

	public static void test() throws InterruptedException {
		Thread tPublish = new Thread(new Runnable() {
			@Override
			public void run() {
				while (true) {
					publish("hi, xxxxxx, data_" + i + "_xxxxxx");
					try {
						Thread.sleep(1000 * 10); // update interval
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}, "t-publish");

		// prepare view threads
		int tViewCount = 3; // count of view thread
		List<Thread> tViewList = new ArrayList<Thread>();
		final List<Long> tLastView = new ArrayList<Long>(); // keep track of last viewed publish date
		for (int i = 0; i < tViewCount; i++) {
			final int _index = i;
			tViewList.add(new Thread(new Runnable() {
				@Override
				public void run() {
					while (true) {
						long _lastDate = view(tLastView.get(_index));
						if (_lastDate > 0) {
							tLastView.set(_index, _lastDate); // update last viewed publish date, if has new publish
						}
						try {
							Thread.sleep(1000 * 4); // view interval
						} catch (InterruptedException e) {
							e.printStackTrace();
						}
					}
				}
			}, "t-view-" + i));
			tLastView.add(0L);
		}

		tPublish.start();
		for (int i = 0; i < tViewCount; i++) {
			tViewList.get(i).start();
			Thread.sleep(1000 * 5); // start interval of view threads
		}
	}

	public static void printTime() {
		printTime("");
	}

	/**
	 * print thread name & time
	 * 
	 * @param info
	 *            additional info to print
	 */
	public synchronized static void printTime(String info) {
		System.out.printf("%s:\t%d,\t,%d,\t%s\n", Thread.currentThread().getName(), ++i, System.currentTimeMillis() / 1000, info);
	}

	public static void main(String[] args) throws InterruptedException {
		test();
	}
}

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