StringBuilder 非執行緒安全

import com.mmall.concurrency.annoations.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 {

    // 請求總數
    public static int clientTotal = 5000;

    // 同時併發執行的執行緒數
    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");
    }
}
 

StringBuffer通過synchronized實現執行緒安全，效能有損耗，有好多程式碼都是在一個方法內部，可以判斷如果不會發生執行緒安全問題，就直接使用StringBuilder來拼接，效率會提升很多。

import com.mmall.concurrency.annoations.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 {

    // 請求總數
    public static int clientTotal = 5000;

    // 同時併發執行的執行緒數
    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非執行緒安全（錯誤寫法）

import com.mmall.concurrency.annoations.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");

    // 請求總數
    public static int clientTotal = 5000;

    // 同時併發執行的執行緒數
    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);
        }
    }
}
 

SimpleDateFormat （修改後）

import com.mmall.concurrency.annoations.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 {

    // 請求總數
    public static int clientTotal = 5000;

    // 同時併發執行的執行緒數
    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);
        }
    }
}

HashSet非執行緒安全

import com.mmall.concurrency.annoations.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 {

    // 請求總數
    public static int clientTotal = 5000;

    // 同時併發執行的執行緒數
    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非執行緒安全

import com.mmall.concurrency.annoations.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 {

    // 請求總數
    public static int clientTotal = 5000;

    // 同時併發執行的執行緒數
    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);
    }
}

ArrayList非執行緒安全

import com.mmall.concurrency.annoations.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 {

    // 請求總數
    public static int clientTotal = 5000;

    // 同時併發執行的執行緒數
    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);
    }
}