并发编程与高并发解决方案学习(同步容器)

ArrayList->Vector,Stack

HashMap->HashTable(key,value不能为null)

Collections.synchronizedXXX（List、Set、Map）

import com.mmall.concurrency.annoations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.List;
import java.util.Vector;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@Slf4j
@ThreadSafe
public class VectorExample1 {
    // 请求总数
    public static int clientTotal = 5000;
    // 同时并发执行的线程数
    public static int threadTotal = 200;
    private static List<Integer> list = new Vector<>();
    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal; i++) {
            final int count = i;
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    update(count);
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("size:{}", list.size());
    }

    private static void update(int i) {
        list.add(i);
    }
}

同步容器不一定是线程安全的，例如：

import com.mmall.concurrency.annoations.NotThreadSafe;

import java.util.Vector;

@NotThreadSafe
public class VectorExample2 {
    private static Vector<Integer> vector = new Vector<>();
    public static void main(String[] args) {
        while (true) {
            for (int i = 0; i < 10; i++) {
                vector.add(i);
            }
            Thread thread1 = new Thread() {
                public void run() {
                    for (int i = 0; i < vector.size(); i++) {
                        vector.remove(i);
                    }
                }
            };
            Thread thread2 = new Thread() {
                public void run() {
                    for (int i = 0; i < vector.size(); i++) {
                        vector.get(i);
                    }
                }
            };
            thread1.start();
            thread2.start();
        }
    }
}

import java.util.Iterator;
import java.util.Vector;

public class VectorExample3 {
    // java.util.ConcurrentModificationException
    private static void test1(Vector<Integer> v1) { // foreach
        for(Integer i : v1) {
            if (i.equals(3)) {
                v1.remove(i);
            }
        }
    }

    // java.util.ConcurrentModificationException
    private static void test2(Vector<Integer> v1) { // iterator
        Iterator<Integer> iterator = v1.iterator();
        while (iterator.hasNext()) {
            Integer i = iterator.next();
            if (i.equals(3)) {
                v1.remove(i);
            }
        }
    }

    // success
    private static void test3(Vector<Integer> v1) { // for
        for (int i = 0; i < v1.size(); i++) {
            if (v1.get(i).equals(3)) {
                v1.remove(i);
            }
        }
    }

    public static void main(String[] args) {
        Vector<Integer> vector = new Vector<>();
        vector.add(1);
        vector.add(2);
        vector.add(3);
        test1(vector);
    }
}

HashTable 线程安全

import com.mmall.concurrency.annoations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@Slf4j
@ThreadSafe
public class HashTableExample {

    // 请求总数
    public static int clientTotal = 5000;

    // 同时并发执行的线程数
    public static int threadTotal = 200;

    private static Map<Integer, Integer> map = new Hashtable<>();

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal; i++) {
            final int count = i;
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    update(count);
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("size:{}", map.size());
    }

    private static void update(int i) {
        map.put(i, i);
    }
}

Collections提供的同步容器

import com.google.common.collect.Lists;
import com.mmall.concurrency.annoations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.Collections;
import java.util.List;
import java.util.Vector;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@Slf4j
@ThreadSafe
public class CollectionsExample1 {

    // 请求总数
    public static int clientTotal = 5000;

    // 同时并发执行的线程数
    public static int threadTotal = 200;

    private static List<Integer> list = Collections.synchronizedList(Lists.newArrayList());

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal; i++) {
            final int count = i;
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    update(count);
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("size:{}", list.size());
    }

    private static void update(int i) {
        list.add(i);
    }
}

import com.google.common.collect.Sets;
import com.mmall.concurrency.annoations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.Collections;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@Slf4j
@ThreadSafe
public class CollectionsExample2 {

    // 请求总数
    public static int clientTotal = 5000;

    // 同时并发执行的线程数
    public static int threadTotal = 200;

    private static Set<Integer> set = Collections.synchronizedSet(Sets.newHashSet());

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal; i++) {
            final int count = i;
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    update(count);
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("size:{}", set.size());
    }

    private static void update(int i) {
        set.add(i);
    }
}

import com.mmall.concurrency.annoations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@Slf4j
@ThreadSafe
public class CollectionsExample3 {

    // 请求总数
    public static int clientTotal = 5000;

    // 同时并发执行的线程数
    public static int threadTotal = 200;

    private static Map<Integer, Integer> map = Collections.synchronizedMap(new HashMap<>());

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal; i++) {
            final int count = i;
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    update(count);
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("size:{}", map.size());
    }

    private static void update(int i) {
        map.put(i, i);
    }
}

注意 如果使用了foreach或者iterator遍历我们的循环的时候，尽量不要在操作过程中做remove相关的更新操作，如果真有这个需求，我们建议，在遍历的过程中做好编辑，在遍历完之后对包含标记的元素做删除操作。

import java.util.Iterator;
import java.util.Vector;

public class VectorExample3 {

    // java.util.ConcurrentModificationException
    private static void test1(Vector<Integer> v1) { // foreach
        for(Integer i : v1) {
            if (i.equals(3)) {
                v1.remove(i);
            }
        }
    }

    // java.util.ConcurrentModificationException
    private static void test2(Vector<Integer> v1) { // iterator
        Iterator<Integer> iterator = v1.iterator();
        while (iterator.hasNext()) {
            Integer i = iterator.next();
            if (i.equals(3)) {
                v1.remove(i);
            }
        }
    }

    // success
    private static void test3(Vector<Integer> v1) { // for
        for (int i = 0; i < v1.size(); i++) {
            if (v1.get(i).equals(3)) {
                v1.remove(i);
            }
        }
    }

    public static void main(String[] args) {

        Vector<Integer> vector = new Vector<>();
        vector.add(1);
        vector.add(2);
        vector.add(3);
        test3(vector);
    }
}