多线程/并行for循环JAVA的每个项目

Question

我想让每个线程访问for循环的单个项目，而另一个线程访问下一个项目。我想要使​​用多个线程来完成此操作，并且创建的多个线程的数量将由用户输入。我已经使用executorservice和流来完成此操作。我想用简单的线程来做到这一点。以下是否正确？有没有更好的办法？

Map<String, String> fileMap = new HashMap<>(); 
fileMap.put("Age", "Age is not remotely associated with it."); 
fileMap.put("Gender", "Gender plays a role but not that important."); 
fileMap.put("Money", "People do not believe but this is the only factor that matters."); 

Runnable myRunnable = new Runnable(){ 
    public void run(){ 
     for (Map.Entry<String, String> entry : fileMap.entrySet()) { 
      synchronized(this){ 
       int counter = 0; 
       Pattern p = Pattern.compile("not"); 
       Matcher m = p.matcher(entry.getValue()); 
       while (m.find()) { 
        counter++; 
       } 
       System.out.println("File Name: " + entry.getKey()); 
       System.out.println("Count: " + counter); 
       System.out.println(Thread.currentThread().getName()); 
      } 
     } 
    }  
}; 

int n = Integer.parseInt(args[0]); 
for (int x=0; x<n; x++) 
{ 
    Thread temp= new Thread(myRunnable, "Thread #" + x); 
    temp.start(); 
    System.out.println("Started Thread:" + x); 
} 

此外，是否有可能有一个线程不会返回到前一个项目，因为上一个线程已经计算出的值？ 任何帮助，将不胜感激。谢谢

Answer 1

这是您的问题的解决方案。这解析线程名称以提供索引并使用最终数组来处理传递到线程中的数据。

Map<String, String> fileMap = new HashMap<>(); 
fileMap.put("Age", "Age is not remotely associated with it."); 
fileMap.put("Gender", "Gender plays a role but not that important."); 
fileMap.put("Money", "People do not believe but this is the only factor that matters."); 


final int[] tgSize = new int[]{0}; 
final Map.Entry[][] entryArr = new Map.Entry[1][]; 

Runnable myRunnable = new Runnable(){ 
    public void run(){ 
     Integer index = Integer.valueOf(Thread.currentThread().getName().substring(8)); 

     for(int i = index; i < fileMap.size(); i += tgSize[0]) { 
      int counter = 0; 
      @SuppressWarnings("unchecked") 
      Map.Entry<String, String> entry = entryArr[0][i]; 
      Pattern p = Pattern.compile("not"); 
      Matcher m = p.matcher(entry.getValue()); 
      while (m.find()) { 
       counter++; 
      } 
      synchronized(this) { 
       System.out.println("File Name: " + entry.getKey()); 
       System.out.println("Count: " + counter); 
       System.out.println(Thread.currentThread().getName());    
      } 
     } 
    }  
}; 

int n = Integer.parseInt(args[0]); 

tgSize[0] = n < fileMap.size() ? n : fileMap.size(); 
entryArr[0] = fileMap.entrySet().toArray(new Map.Entry[fileMap.size()]); 


for (int x=0; x<n && x < fileMap.size(); x++) 
{ 
    Thread temp= new Thread(myRunnable, "Thread #" + x); 
    temp.start(); 
    System.out.println("Started Thread:" + x); 
} 

Answer 2

可以通过paralledStream通过AbacusUtil

final Pattern p = Pattern.compile("not"); 

Stream.of(fileMap).parallel(threadNum).map(entry -> { 
    Matcher m = p.matcher(entry.getValue()); 
    int count = 0; 
    while (m.find()) { 
     count++; 
    } 
    return Pair.of(entry.getKey(), count); 
}).forEach(entry -> { 
    N.println("File Name: " + entry.getKey() + ", Count: " + entry.getValue()); 
}); 

如果您想了解如何通过自己编写多线程代码来实现的。这里是一个简单的示例：

final int threadNum = 3; 
final ExecutorService executorService = Executors.newFixedThreadPool(threadNum); 
final Iterator<Entry<String, String>> iter = fileMap.entrySet().iterator(); 

for (int i = 0; i < threadNum; i++) { 
    executorService.execute(new Runnable() { 
     @Override 
     public void run() { 
      Entry<String, String> entry = null; 
      while (true) { 
       synchronized (iter) { 
        if (iter.hasNext() == false) { 
         break; 
        } 
        entry = iter.next(); 
       } 

       final Matcher m = p.matcher(entry.getValue()); 
       int count = 0; 
       while (m.find()) { 
        count++; 
       } 

       System.out.println("File Name: " + entry.getKey() + ", Count: " + count + ", thread: " + Thread.currentThread().getName()); 
      } 
     } 
    }); 
} 

声明：我是AbacusUtil的开发人员。

Answer 3

使用您的问题在下面说明了使用迭代遍历数组的原始线程并行化循环的标准方法。

import java.util.*; 
import java.util.regex.*; 

public class MyClass { 

public static void main(String[] args) { 
    Map<String, String> fileMap = new HashMap<>(); 
    fileMap.put("Age", "Age is not remotely associated with it."); 
    fileMap.put("Gender", "Gender plays a role but not that important."); 
    fileMap.put("Money", "People do not believe but this is the only factor that matters."); 
    String[] keys = fileMap.keySet().toArray(new String[fileMap.size()]); 

    int n = 2; //Integer.parseInt(args[0]); 
    for (int x=0; x<n; x++) 
    { 
     Runnable myRunnable = new MyRunnable(fileMap, keys, x, n); 
     Thread temp= new Thread(myRunnable); 
     temp.start(); 
     //System.out.println("Started Thread:" + x); 
    } 
} 

    private static class MyRunnable implements Runnable { 
     private Map<String, String> fileMap; 
     private String[] keys; 
     private int threadID; 
     private int threadCount; 
     Pattern p = Pattern.compile("not"); 
     public MyRunnable(Map<String, String> fileMap, String[] keys, int threadID, int threadCount) { 
      this.fileMap = fileMap; 
      this.keys = keys; 
      this.threadID = threadID; 
      this.threadCount = threadCount; 
     } 
     public void run(){ 
      for (int i=threadID; i<keys.length; i+= threadCount) { 
       int counter = 0; 
       Matcher m = p.matcher(fileMap.get(keys[i])); 
       while (m.find()) { 
        counter++; 
       } 
       synchronized(MyClass.class){ 
        System.out.println("File Name: " + keys[i]); 
        System.out.println("Count: " + counter); 
        System.out.println("ThreadID: " + threadID); 
       } 
      } 
     }  
    } 
    }