为什么这个线程（WriteData）没有执行它的功能？

Question

我在练习信号量class 我创建了两个线程，其中一个将数据写入 "Shared" class 中的 HashMap，另一个从 Shared class.

中读取数据

所以我的问题是，当我读取数据时，它只显示以前添加到共享 class 中的数据，而不是更新后的数据。我不知道我在哪里失踪了。

我应该从 "Writedata" 读取 class 如果是的话如何线程 return HashMap.

class Shared {

    Map<String, Integer> hashmap = new HashMap<String, Integer>();
    {
        hashmap.put("kishore", 797979);
        hashmap.put("nanesg", 8768787);
        hashmap.put("mahesh", 842803);
        hashmap.put("srikar", 7979980);
    }

    public void puthash(String name, Integer in, Map<String, Integer> hashmap) {
        hashmap.put(name, in);
    }

    public Map<String, Integer> gethash() {
        return this.hashmap;
    }

}

class ReadHashMap implements Runnable {

    Semaphore sem;
    String name;
    Shared shared = new Shared();

    ReadHashMap(Semaphore sem, String name) {
        this.sem = sem;
        this.name = name;

        new Thread(this, name).start();

    }

    public void run() {
        try {
            System.out.println(Thread.currentThread().getName() + " Thread trying to acquiring the permit ");
            sem.acquire();
            System.out.println(Thread.currentThread().getName() + " Thread acquires the permit ");
            Map<String, Integer> hashmap = shared.gethash();
            Set<Entry<String, Integer>> set = hashmap.entrySet();
            System.out.println("reading data in hashmap, Here is the data: ");
            for (Map.Entry<String, Integer> mp : set) {

                System.out.println(mp.getKey() + "  : " + mp.getValue());
            }

        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            System.out.println(Thread.currentThread().getName() + " Thread relesing the permit ");
            sem.release();
        }

    }
}

class WriteData implements Runnable {

    Semaphore sem;
    String name;
    Shared shared = new Shared();

    WriteData(Semaphore sem, String name) {
        this.sem = sem;
        this.name = name;
        new Thread(this, name).start();

    }

    public void run() {
        try {
            System.out.println(Thread.currentThread().getName() + "Thread trying to get permit");
            sem.acquire();
            Map<String, Integer> hashmap = shared.gethash();
            System.out.println(Thread.currentThread().getName() + " Thread acquires the permit ");
            shared.puthash("added1", 98799, hashmap);
            shared.puthash("added2", 987989, hashmap);
            shared.puthash("added3", 98979, hashmap);

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName() + " Thread relesing the permit ");
        sem.release();
    }
}

public class SemaphoreDemo {
    public static void main(String args[]) {
        Semaphore sem = new Semaphore(1);

        new WriteData(sem, "write");
        new ReadHashMap(sem, "read");
    }
}

这是它的输出：

writeThread trying to get permit
read Thread trying to acquiring the permit 
write Thread acquires the permit 
write Thread relesing the permit 
read Thread acquires the permit 
reading data in hashmap, Here is the data: 
nanesg  : 8768787
mahesh  : 842803
kishore  : 797979
srikar  : 7979980
read Thread relesing the permit

为什么 WriteData 线程（特别是函数）没有添加数据。该功能有什么问题？

Answer 1

因为您在 ReadHashMap 和 WriteData 中创建了不同的 Shared 个实例。

解决方案

使用相同的Shared:

class ReadHashMap implements Runnable {

    Semaphore sem;
    String name;
    Shared shared;

    ReadHashMap(Semaphore sem, String name, Shared shared) {
        this.sem = sem;
        this.name = name;
        this.shared = shared;
        new Thread(this, name).start();
    }
    ....
}

class WriteData implements Runnable {

    Semaphore sem;
    String name;
    Shared shared;

    WriteData(Semaphore sem, String name, Shared shared) {
        this.sem = sem;
        this.name = name;
        this.shared = shared;
        new Thread(this, name).start();
    }

    ....
}

public class SemaphoreDemo {
    public static void main(String args[]) {
        Semaphore sem = new Semaphore(1);
        Shared shared = new Shared();

        new WriteData(sem, "write", shared);
        new ReadHashMap(sem, "read", shared);
    }
}

结果

writeThread trying to get permit
write Thread acquires the permit 
read Thread trying to acquiring the permit 
write Thread relesing the permit 
read Thread acquires the permit 
reading data in hashmap, Here is the data: 
nanesg  : 8768787
mahesh  : 842803
kishore  : 797979
added2  : 987989
added3  : 98979
srikar  : 7979980
added1  : 98799
read Thread relesing the permit

为什么这个线程（WriteData）没有执行它的功能？

Why this thread(WriteData) not doing it's functionality?

java

multithreading

semaphore

解决方案

结果