Threads behave in sequential Style

[sanjey asok]

I have a program which create many Thread and each one execute its process,

Among all threads ,one thread take more time(MyCallable1) to finish it process and other thread (MyCallable) take less time to finish its process,

I call the long-running Thread first and call others one by one ,but the other thread wait for the thread MyCallable1 to finish after that,It start it process.

Why other threads MyCallable wait for MyCallable1,then it is not real multithreaded?

  public class MyCallable implements Callable<String> {
	
		public String call() throws Exception {
			long sum = 0;
			Calendar cal = Calendar.getInstance();
		    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		    
	
			/*for (long i = 0; i <= 100; i++) {
				sum += i;
				}*/
			
			
			return sdf.format(cal.getTime()) ;
		}
	
		
	
	}  

 public class MyCallable1 implements Callable<String> {
	
		public String call() throws Exception {
			
			Calendar cal = Calendar.getInstance();
		    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		    
		    System.out.println("Starting......");
	        
	 
	         Thread thisThread = Thread.currentThread();
	         try
	             {
	             thisThread.sleep(100000);
	         }
	         catch (Throwable t)
	             {
	             throw new OutOfMemoryError("An Error has occured");
	         }
	         System.out.println("Ending......");
			
			return sdf.format(cal.getTime()) ;
		}
	
		
	
	}   

 public class CallableFutures {
	private static final int NTHREDS = 30;

	public static void main(String[] args) throws InterruptedException {

		ExecutorService executor = Executors.newFixedThreadPool(NTHREDS);
		List<Future<String>> list = new ArrayList<Future<String>>();
		for (int i = 0; i < 20; i++) {
			if(i== 0) 
			{
				Callable<String> worker = new MyCallable1();
				Future<String> submit = executor.submit(worker);
				list.add(submit);
				System.out.println("I value is "+i);
			} else
			{
			Callable<String> worker = new MyCallable();
			Future<String> submit = executor.submit(worker);
			list.add(submit);
			System.out.println("I value is "+i);
			}
		}
		
			for (Future<String> future : list) {
			try {

				System.out.println(future.get());
			} catch (InterruptedException e) {
				e.printStackTrace();
			} catch (ExecutionException e) {
				e.printStackTrace();
			}
		}

	}
}   

   result

I value is 0
I value is 1
I value is 2
I value is 3
I value is 4
I value is 5
I value is 6
I value is 7
I value is 8
I value is 9
I value is 10
I value is 11
I value is 12
I value is 13
I value is 14
I value is 15
I value is 16
I value is 17
I value is 18
I value is 19
Starting......
Ending......
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
2010-07-25 20:51:06
 

[Henry Wong]

sanjey asok wrote:
Why other threads MyCallable wait for MyCallable1,then it is not real multithreaded?

How do you know this is happening? Your MyCallable don't print anything out. So, how do you know that they are actually waiting for MyCallable1 to finish?

Henry

[sanjey asok]

Henry Wong wrote:

sanjey asok wrote:
Why other threads MyCallable wait for MyCallable1,then it is not real multithreaded?

How do you know this is happening? Your MyCallable don't print anything out. So, how do you know that they are actually waiting for MyCallable1 to finish?

Henry

MyCallable return current time


After "Ending " printed ,every thread returns value

[pete stein]

When I run your code, it seems to work correctly -- all threads are running concurrently.

One little aside: you don't call sleep on a specific Thread instance but rather call it as a static method,

Thread.sleep(...);

This calls sleep on the current thread.

[Henry Wong]

sanjey asok wrote:

Henry Wong wrote:
How do you know this is happening? Your MyCallable don't print anything out. So, how do you know that they are actually waiting for MyCallable1 to finish?

MyCallable return current time

After "Ending " printed ,every thread returns value

You do know that the "current time" being returned, is for a time that was taken at the beginning of the method, right? So... all those times returned, are their start times, and not their end times. And since all the threads started around the same time, they should be close to each other.

Henry