Java - Что такое семафор с задолженностью

Question

В примере кода сказано, что повторная синхронизация потоков основана на передаче сигналов с использованием семафора с задолженностью.

final Semaphore indebtedSemaphore = new Semaphore(1 - PROCESSOR_COUNT); 

Какова цель этого негативного семафора, с моим ноутбуком он будет инициализирован -3

/** 
* Sums two vectors, distributing the work load into as many new child threads as there 
* are processor cores within a given system. Note that the added cost of thread 
* construction and destruction is higher than the gain of distributing the work for 
* practically any vector size. 
* @param leftOperand the first operand 
* @param rightOperand the second operand 
* @return the resulting vector 
* @throws NullPointerException if one of the given parameters is null 
* @throws IllegalArgumentException if the given parameters do not share the same length 
*/ 
public static double[] add(final double[] leftOperand, final double[] rightOperand) { 
    if (leftOperand.length != rightOperand.length) throw new IllegalArgumentException(); 
    final double[] result = new double[leftOperand.length]; 

    final int sectorWidth = leftOperand.length/PROCESSOR_COUNT; 
    final int sectorThreshold = leftOperand.length % PROCESSOR_COUNT; 
    final Semaphore indebtedSemaphore = new Semaphore(1 - PROCESSOR_COUNT); 

    for (int threadIndex = 0; threadIndex < PROCESSOR_COUNT; ++threadIndex) { 
     final int startIndex = threadIndex * sectorWidth + (threadIndex < sectorThreshold ? threadIndex : sectorThreshold); 
     final int stopIndex = startIndex + sectorWidth + (threadIndex < sectorThreshold ? 1 : 0); 
     final Runnable runnable = new Runnable() { 
      public void run() { 
       try { 
        for (int index = startIndex; index < stopIndex; ++index) { 
         result[index] = leftOperand[index] + rightOperand[index]; 
        } 
       } finally { 
        indebtedSemaphore.release(); 
       } 
      } 
     }; 
     // EXECUTOR_SERVICE.execute(runnable);       // uncomment for managed thread alternative! 
     new Thread(runnable).start();         // comment for managed thread alternative! 
    } 

    indebtedSemaphore.acquireUninterruptibly(); 
    return result; 
} 

Answer 1

комментарии в sourcecode->

public static double[] add (final double[] leftOperand, final double[] rightOperand) { 
     if (leftOperand.length != rightOperand.length) throw new IllegalArgumentException(); 
     final double[] result = new double[leftOperand.length]; 
    //-------------------------------------------------------------- 
    //EXAMPLE: 3 Cores, vector length 10 
    //-------------------------------------------------------------- 

    final int sectorWidth = leftOperand.length/PROCESSOR_COUNT; 
    final int sectorThreshold = leftOperand.length % PROCESSOR_COUNT; 
    //indebtedSemaphore (-2) .. to wait for a unindebted semaphore 
    final Semaphore indebtedSemaphore = new Semaphore(1 - PROCESSOR_COUNT); 

    //for each core a thread 
    for (int threadIndex = 0; threadIndex < PROCESSOR_COUNT; ++threadIndex) { 
     //ranges 0-4 , 4-7, 7-10 
     final int startIndex = threadIndex * sectorWidth + (threadIndex < sectorThreshold ? threadIndex : sectorThreshold); 
     final int stopIndex = startIndex + sectorWidth + (threadIndex < sectorThreshold ? 1 : 0); 
     final Runnable runnable = new Runnable() { 
      public void run() { 
       try { 
        for (int index = startIndex; index < stopIndex; ++index) { 
         result[index] = leftOperand[index] + rightOperand[index]; 
        } 
       } finally { 
        //semaphore dept:-2,-1,0, 
        indebtedSemaphore.release(); 
       } 
      } 
     }; 
     // EXECUTOR_SERVICE.execute(runnable);       // uncomment for managed thread alternative! 
     new Thread(runnable).start();         // comment for managed thread alternative! 
    } 

    //wait for unindebted semaphore 
    indebtedSemaphore.acquireUninterruptibly(); 
    return result; 
}