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POWhile Parallelizing QuickSort in Java, Threads never returns back at join(). Why?
 

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  1. POWhile Parallelizing QuickSort in Java, Threads never returns back at join(). Why?
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    <p>I am having simple code of paralellizing QuickSort algorithm in Java, in run method I everytime create two seperate new threads for parallelizing processing of Array elements. But as it encounters join() statements for both created threads, threads never backs and halts on joins(), seems join() never releases them.</p> <p>Below is the code.</p> <pre><code>class StartJoinQuickSort implements Runnable { private int m_Low, m_High; private int[] m_Array = null; private final static int NR_OF_VALUES = 10; // TOTAL_NO_VALUES private int PivotElement; private static Random m_random = new Random( ); public StartJoinQuickSort(int[] a_Array,int a_Low,int a_High) { this.m_Array = a_Array; this.m_Low = a_Low; this.m_High = a_High; } private void SwapArrayElements(int a_i,int a_j) { int temp = this.m_Array[a_i]; this.m_Array[a_i] = this.m_Array[a_j]; this.m_Array[a_j] = temp; }// end of SwapArrayElements private static int nextRandomFunctionValue(int aStart, int aEnd) { if ( aStart &gt; aEnd ) { throw new IllegalArgumentException("Start cannot exceed End."); } //get the range, casting to long to avoid overflow problems long range = (long)aEnd - (long)aStart + 1; // compute a fraction of the range, 0 &lt;= frac &lt; range long fraction = (long)(range * m_random.nextDouble()); int randomNumber = (int)(fraction + aStart); return randomNumber; }// end of nextRandomFunctionValue private static int[] GetArrayWithRandomValues() { int[] ArrayToBePopulatedWithRandomValues = new int[NR_OF_VALUES]; for(int index =0; index&lt;NR_OF_VALUES;index++) { int RandomValue = StartJoinQuickSort.nextRandomFunctionValue(0,NR_OF_VALUES); ArrayToBePopulatedWithRandomValues[index] = RandomValue; }//end of for return ArrayToBePopulatedWithRandomValues; }//end of GetArrayWithRandomValues private int middleIndex(int left, int right) { return left + (right - left) / 2; } public int Partition(int a_Start,int a_end) { // System.out.println("Partition ..thId : " + Thread.currentThread().getId()); int pivotIndex = 0; int i = a_Start; int j = a_end; try { pivotIndex = middleIndex(a_Start , a_end); this.PivotElement = this.m_Array[pivotIndex]; do { while(this.m_Array[i] &lt; PivotElement ) i++; if(j&gt;0) { try { while( this.m_Array[j] &gt; PivotElement ) j--; } catch(Exception ex){System.out.println(" j : " + j);} }//end of if if(i&lt;=j) { SwapArrayElements(i,j); // System.out.println("Swap .." + + Thread.currentThread().getId()); i++; j--; }//end of if }while(i&lt;=j); } catch(Exception except) { System.out.println("exception in Partition " + except); } return j; } public void run() { //System.out.println("in run.."); //System.out.println("after PARTITION"); StartJoinQuickSort oStartQuickSort_1 = null; StartJoinQuickSort oStartQuickSort_2 = null; if(this.m_Low &lt; this.m_High ) { int Index = Partition(this.m_Low,this.m_High); Thread thPart_1 = new Thread ( new StartJoinQuickSort( this.m_Array,this.m_Low,Index ) ); Thread thPart_2 = new Thread ( new StartJoinQuickSort( this.m_Array,Index + 1,this.m_High ) ); thPart_1.start(); thPart_2.start(); //}//end of if //if( Index + 1 &lt; this.m_High) //{ try { thPart_1.join(); thPart_2.join(); }catch (InterruptedException e) { e.printStackTrace();} } }//end of run </code></pre> <p>Regards Usman</p>
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    1. This table or related slice is empty.
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    1. USTudor
    1. USUsman
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    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
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    2. PO
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      1. POWhile Parallelizing QuickSort in Java, Threads never returns back at join(). Why?
      1. USjjczopek
      1. VTFavorite
    2. VO
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      1. POWhile Parallelizing QuickSort in Java, Threads never returns back at join(). Why?
      1. This table or related slice is empty.
      1. VTUpMod
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      1. POWhile Parallelizing QuickSort in Java, Threads never returns back at join(). Why?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COBTW, this is a very naïve way to do parallel quicksort. You'll loose more time creating all the threads than you gain from parallelizing. See http://www.deftitlenil.com/2011/04/blog-post_05.html for a solution that uses JDK7's new ForkJoinPool.
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      1. POWhile Parallelizing QuickSort in Java, Threads never returns back at join(). Why?
      1. USgreyfairer
    2. COI have done with ForkJoin, But I want this part to be done ( Naive way).
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      1. POWhile Parallelizing QuickSort in Java, Threads never returns back at join(). Why?
      1. USUsman
    3. COI am afraid you need to show us the source code of `StartJoinQuickSort` in order for us to be able to tell why it never ends. Also the code of `Partition`.
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      1. POWhile Parallelizing QuickSort in Java, Threads never returns back at join(). Why?
      1. USMike Nakis
 

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