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POJava - What is a indebted semaphore
 

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  1. POJava - What is a indebted semaphore
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    <p>In a Code example it is said that a thread re-synchronization is based on signaling, using an indebted semaphore. </p> <pre><code>final Semaphore indebtedSemaphore = new Semaphore(1 - PROCESSOR_COUNT); </code></pre> <p>What is the purpose of this negative semaphore, with my notebook it would be initialized with -3</p> <pre><code>/** * 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 &lt; PROCESSOR_COUNT; ++threadIndex) { final int startIndex = threadIndex * sectorWidth + (threadIndex &lt; sectorThreshold ? threadIndex : sectorThreshold); final int stopIndex = startIndex + sectorWidth + (threadIndex &lt; sectorThreshold ? 1 : 0); final Runnable runnable = new Runnable() { public void run() { try { for (int index = startIndex; index &lt; 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; } </code></pre>
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    1. USuser1477955
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    1. COI'm assuming it was just the developer acknowledging that the semaphore would start with possibly negative values ? Not sure though.
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      1. POJava - What is a indebted semaphore
      1. USHunter McMillen
    2. COA negative semaphore means there is a negative amount of resources available. In other words, at that point, the application has a hold on all the resources and must release them before any other unit can acquire them. http://stackoverflow.com/questions/1221322/how-does-semaphore-work
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      1. POJava - What is a indebted semaphore
      1. USSotirios Delimanolis
    3. CO@SotiriosDelimanolis why the -3 ?
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      1. POJava - What is a indebted semaphore
      1. USuser1477955
 

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