JUC并发编程-4.Immutable、线程不安全类、安全容器

1.Immutable

（一）Integer、String、...用final修饰后可以不会更改
（二）List、Set、Map...用final修饰后依然可改变
（三）List、Set、Map...Collections.unmodifiable* 不会改变
（四）List、Set、Map...Guava..Immutable* 不会改变

  • ImmutableExample1.java 验证（一）（二）
package com.ctgu.juc_project.example.immutable;

import com.ctgu.juc_project.annotation.NotThreadSafe;
import com.google.common.collect.Maps;
import lombok.extern.slf4j.Slf4j;

import java.util.Map;

@Slf4j
@NotThreadSafe
public class ImmutableExample1 {

    private final static Integer a = 1;
    private final static String b = "2";
    private final static Map<Integer, Integer> map = Maps.newHashMap();

    static {
        map.put(1, 2);
        map.put(3, 4);
        map.put(5, 6);
    }

    public static void main(String[] args) {
//        a = 2;
//        b = "3";
//        map = Maps.newHashMap();
        map.put(1, 3);
        log.info("{}", map.get(1));
    }

    private void test(final int a) {
//        a = 1;
    }
}
  • ImmutableExample2.java 验证（三）
package com.ctgu.juc_project.example.immutable;

import com.ctgu.juc_project.annotation.ThreadSafe;
import com.google.common.collect.Maps;
import lombok.extern.slf4j.Slf4j;

import java.util.Collections;
import java.util.Map;

@Slf4j
@ThreadSafe
public class ImmutableExample2 {

    private static Map<Integer, Integer> map = Maps.newHashMap();

    static {
        map.put(1, 2);
        map.put(3, 4);
        map.put(5, 6);
        map = Collections.unmodifiableMap(map);
    }

    public static void main(String[] args) {
        map.put(1, 3);
        log.info("{}", map.get(1));
    }

}

Console:
Exception in thread "main" java.lang.UnsupportedOperationException
    at java.util.Collections$UnmodifiableMap.put(Collections.java:1457)
    at com.ctgu.juc_project.example.immutable.ImmutableExample2.main(ImmutableExample2.java:24)

Process finished with exit code 1
  • ImmutableExample3.java 验证（四）
package com.ctgu.juc_project.example.immutable;

import com.ctgu.juc_project.annotation.ThreadSafe;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import lombok.extern.slf4j.Slf4j;

@Slf4j
@ThreadSafe
public class ImmutableExample3 {

    private final static ImmutableList<Integer> list = ImmutableList.of(1, 2, 3);

    private final static ImmutableSet set = ImmutableSet.copyOf(list);

    private final static ImmutableMap<Integer, Integer> map = ImmutableMap.of(1, 2, 3, 4);

    private final static ImmutableMap<Integer, Integer> map2 = ImmutableMap.<Integer, Integer>builder()
            .put(1, 2).put(3, 4).put(5, 6).build();


    public static void main(String[] args) {
        map2.put(1,1);
        log.info("{}", map2.get(3));
    }
}

Console:
Exception in thread "main" java.lang.UnsupportedOperationException
    at com.google.common.collect.ImmutableMap.put(ImmutableMap.java:527)
    at com.ctgu.juc_project.example.immutable.ImmutableExample3.main(ImmutableExample3.java:24)

Process finished with exit code 1

2.线程不安全类

  • StringBuilder.java
package com.ctgu.juc_project.example.commonUnsafe;

import com.ctgu.juc_project.annotation.NotThreadSafe;
import lombok.extern.slf4j.Slf4j;

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

@Slf4j
@NotThreadSafe
public class StringExample1 {

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

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

    public static StringBuilder stringBuilder = new StringBuilder();

    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++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    update();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("size:{}", stringBuilder.length());
    }

    private static void update() {
        stringBuilder.append("1");
    }
}
  • List.java
package com.ctgu.juc_project.example.commonUnsafe;

import com.ctgu.juc_project.annotation.NotThreadSafe;
import lombok.extern.slf4j.Slf4j;

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

@Slf4j
@NotThreadSafe
public class ArrayListExample {

    // 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 ArrayList<>();

    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);
    }
}
  • SimpleDateFormat.java
package com.ctgu.juc_project.example.commonUnsafe;

import com.ctgu.juc_project.annotation.NotThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.text.SimpleDateFormat;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@Slf4j
@NotThreadSafe
public class DateFormatExample1 {

    private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd");

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

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

    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++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    update();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
    }

    private static void update() {
        try {
            simpleDateFormat.parse("20180208");
        } catch (Exception e) {
            log.error("parse exception", e);
        }
    }
}
  • HashSet.java
package com.ctgu.juc_project.example.commonUnsafe;

import com.ctgu.juc_project.annotation.NotThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.HashSet;
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
@NotThreadSafe
public class HashSetExample {

    // 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 = new HashSet<>();

    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);
    }
}
  • HashMap.java
package com.ctgu.juc_project.example.commonUnsafe;

import com.ctgu.juc_project.annotation.NotThreadSafe;
import lombok.extern.slf4j.Slf4j;

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
@NotThreadSafe
public class HashMapExample {

    // 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 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);
    }
}

3.线程不安全类改进

  • StringBuilder 改为 StringBuffer
package com.ctgu.juc_project.example.commonUnsafe;

import com.ctgu.juc_project.annotation.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

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

@Slf4j
@ThreadSafe
public class StringExample2 {

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

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

    public static StringBuffer stringBuffer = new StringBuffer();

    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++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    update();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("size:{}", stringBuffer.length());
    }

    private static void update() {
        stringBuffer.append("1");
    }
}
  • SimpleDateFormat 放在局部变量里是线程安全的
package com.ctgu.juc_project.example.commonUnsafe;

import com.ctgu.juc_project.annotation.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.text.SimpleDateFormat;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@Slf4j
@ThreadSafe
public class DateFormatExample2 {

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

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

    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++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    update();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
    }

    private static void update() {
        try {
            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd");
            simpleDateFormat.parse("20180208");
        } catch (Exception e) {
            log.error("parse exception", e);
        }
    }
}
  • SimpleDateFormat 改为joda-time.DateTimeFormatter
package com.ctgu.juc_project.example.commonUnsafe;

import com.ctgu.juc_project.annotation.ThreadSafe;
import lombok.extern.slf4j.Slf4j;
import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;

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

@Slf4j
@ThreadSafe
public class DateFormatExample3 {

    // 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 DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyyyMMdd");

    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();
    }

    private static void update(int i) {
        log.info("{}, {}", i, DateTime.parse("20180208", dateTimeFormatter).toDate());
    }
}

4.线程安全的容器

  • List、Set、Map >> Collections.synchronized*
package com.ctgu.juc_project.example.syncContainer;

import com.ctgu.juc_project.annotation.ThreadSafe;
import com.google.common.collect.Lists;
import lombok.extern.slf4j.Slf4j;

import java.util.Collections;
import java.util.List;
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);
    }
}
  • Vector
package com.ctgu.juc_project.example.syncContainer;

import com.ctgu.juc_project.annotation.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);
    }
}
  • vector 索引越界
package com.ctgu.juc_project.example.syncContainer;


import com.ctgu.juc_project.annotation.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();
        }
    }
}
  • Vector 正确删除元素方式
package com.ctgu.juc_project.example.syncContainer;

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<Integer>(){{
            add(1);
            add(2);
            add(3);
        }};
        test3(vector);
        System.out.println(vector);
    }
}
  • HashMap >> HashTable
package com.ctgu.juc_project.example.syncContainer;

import com.ctgu.juc_project.annotation.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

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);
    }
}

5.并发容器

  • List >> CopyOnWriteArrayList
package com.ctgu.juc_project.example.concurrent;

import com.ctgu.juc_project.annotation.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

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

@Slf4j
@ThreadSafe
public class CopyOnWriteArrayListExample {

    // 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 CopyOnWriteArrayList<>();

    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);
    }
}
  • HashSet >> CopyOnWriteArraySet
package com.ctgu.juc_project.example.concurrent;

import com.ctgu.juc_project.annotation.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

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

@Slf4j
@ThreadSafe
public class CopyOnWriteArraySetExample {

    // 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 = new CopyOnWriteArraySet<>();

    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);
    }
}
  • TreeSet >> ConcurrentSkipListSet
package com.ctgu.juc_project.example.concurrent;

import com.ctgu.juc_project.annotation.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

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

@Slf4j
@ThreadSafe
public class ConcurrentSkipListSetExample {

    // 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 = new ConcurrentSkipListSet<>();

    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);
    }
}
  • HashMap >> ConcurrentHashMap
package com.ctgu.juc_project.example.concurrent;

import com.ctgu.juc_project.annotation.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@Slf4j
@ThreadSafe
public class ConcurrentHashMapExample {

    // 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 ConcurrentHashMap<>();

    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);
    }
}
  • TreeMap >> ConcurrentSkipListMap
package com.ctgu.juc_project.example.concurrent;

import com.ctgu.juc_project.annotation.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.Map;
import java.util.concurrent.ConcurrentSkipListMap;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@Slf4j
@ThreadSafe
public class ConcurrentSkipListMapExample {

    // 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 ConcurrentSkipListMap<>();

    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);
    }
}
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