ThreadLocal

Author: ZHENFENG13

src/chapter4/ThreadLocalDemo.java

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+package chapter4;
+
+import java.util.Random;
+import java.util.concurrent.*;
+
+/**
+ * Created by 13 on 2017/5/6.
+ */
+public class ThreadLocalDemo {
+    public static final int GE_COUNT = 10000000;
+    public static final int THREAD_COUT = 4;
+
+    static ExecutorService executorService = Executors.newFixedThreadPool(THREAD_COUT);
+    public static Random random = new Random(123);
+
+    public static ThreadLocal<Random> randomThreadLocal = new ThreadLocal<Random>() {
+        protected Random initialValue() {
+            return new Random(123);
+        }
+    };
+
+
+    public static class RandomTask implements Callable<Long> {
+
+        private int mode = 0;
+
+        public RandomTask(int mode) {
+            this.mode = mode;
+        }
+
+        public Random getRandom() {
+            if (mode == 0) {
+                return random;
+            } else if (mode == 1) {
+                return randomThreadLocal.get();
+            } else {
+                return null;
+            }
+        }
+
+
+        @Override
+        public Long call() throws Exception {
+            long b = System.currentTimeMillis();
+
+            for (int i = 0; i < GE_COUNT; i++) {
+                getRandom().nextInt();
+            }
+            long e = System.currentTimeMillis();
+            System.out.println(Thread.currentThread().getName() + " spend" + (e - b) + "ms");
+            return e - b;
+        }
+    }
+
+    public static void main(String args[]) throws ExecutionException, InterruptedException {
+        Future<Long>[] futures = new Future[THREAD_COUT];
+        for (int i = 0; i < THREAD_COUT; i++) {
+            futures[i] = executorService.submit(new RandomTask(0));
+        }
+
+        long totalTime = 0;
+
+        for (int i = 0; i < THREAD_COUT; i++) {
+            totalTime += futures[i].get();
+        }
+        System.out.println("多线程访问同一个Random实例:" + totalTime + "ms");
+
+        //ThreadLocal的情况
+        for (int i = 0; i < THREAD_COUT; i++) {
+            futures[i] = executorService.submit(new RandomTask(1));
+        }
+        totalTime = 0;
+        for (int i = 0; i < THREAD_COUT; i++) {
+            totalTime += futures[i].get();
+        }
+        System.out.println("使用ThreadLocal包装Random实例:" + totalTime + "ms");
+
+    }
+}

src/chapter4/ThreadLocalDemo_GC.java

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+package chapter4;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+/**
+ * Created by 13 on 2017/5/6.
+ */
+public class ThreadLocalDemo_GC {
+    static volatile ThreadLocal<SimpleDateFormat> threadLocal = new ThreadLocal<SimpleDateFormat>() {
+        protected void finalize() throws Throwable {
+            System.out.println(this.toString() + " is gc");
+        }
+    };
+
+    static volatile CountDownLatch countDownLatch = new CountDownLatch(100);
+
+    public static class ParseDate implements Runnable {
+        int i = 0;
+
+        public ParseDate(int i) {
+            this.i = i;
+        }
+
+        @Override
+        public void run() {
+
+            try {
+                if (threadLocal.get() == null) {
+                    threadLocal.set(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss") {
+                        protected void finalize() throws Throwable {
+                            System.out.println(this.toString() + " is gc");
+                        }
+                    });
+                    System.out.println(Thread.currentThread().getId() + " create SimpleDatFormat");
+                }
+                Date date = threadLocal.get().parse("2017-05-06 12:33:" + i % 60);
+                System.out.println(i + ":" + date);
+            } catch (ParseException e) {
+                e.printStackTrace();
+            } finally {
+                countDownLatch.countDown();
+            }
+
+        }
+    }
+
+
+    public static void main(String args[]) throws InterruptedException {
+        ExecutorService executorService = Executors.newFixedThreadPool(10);
+        for (int i = 0; i < 100; i++) {
+            executorService.execute(new ParseDate(i));
+        }
+        countDownLatch.await();
+
+        System.out.println("mission complete!");
+
+        threadLocal = null;
+        System.gc();
+        System.out.println("first GC complete!!");
+
+        threadLocal = new ThreadLocal<SimpleDateFormat>();
+
+        countDownLatch = new CountDownLatch(100);
+
+        for (int i = 0; i < 100; i++) {
+            executorService.execute(new ParseDate(i));
+        }
+
+        countDownLatch.await();
+        Thread.sleep(1000);
+        System.gc();
+        System.out.println("second GC complete!");
+    }
+}