在Java中使用并行机制会使程序变慢（慢四倍！！！）
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我正在写共轭梯度方法的实现。
我使用Java多线程进行矩阵反向替换。
使用CyclicBarrier，CountDownLatch进行同步。
为什么要花这么多时间来同步线程？
还有其他方法吗？
程式码片段
private void syncThreads() {
// barrier.await();
try {
barrier.await();
} catch (InterruptedException e) {
} catch (BrokenBarrierException e) {
}
}
没有找到相关结果
已邀请:
5 个回复
芦歉竭皑
街茬
final double[] results = new double[10*1000*1000]; { long start = System.nanoTime(); // using a plain loop. for(int i=0;i<results.length;i++) { results[i] = (double) i * i; } long time = System.nanoTime() - start; System.out.printf(\"With one thread it took %.1f ns per square%n\", (double) time / results.length); } { ExecutorService ex = Executors.newFixedThreadPool(4); long start = System.nanoTime(); // using a plain loop. for(int i=0;i<results.length;i++) { final int i2 = i; ex.execute(new Runnable() { @Override public void run() { results[i2] = i2 * i2; } }); } ex.shutdown(); ex.awaitTermination(1, TimeUnit.MINUTES); long time = System.nanoTime() - start; System.out.printf(\"With four threads it took %.1f ns per square%n\", (double) time / results.length); }使用多个线程会更糟。 但是，增加每个线程的工作量并final double[] results = new double[10 * 1000 * 1000]; { long start = System.nanoTime(); // using a plain loop. for (int i = 0; i < results.length; i++) { results[i] = Math.pow(i, 1.5); } long time = System.nanoTime() - start; System.out.printf(\"With one thread it took %.1f ns per pow 1.5%n\", (double) time / results.length); } { int threads = 4; ExecutorService ex = Executors.newFixedThreadPool(threads); long start = System.nanoTime(); int blockSize = results.length / threads; // using a plain loop. for (int i = 0; i < threads; i++) { final int istart = i * blockSize; final int iend = (i + 1) * blockSize; ex.execute(new Runnable() { @Override public void run() { for (int i = istart; i < iend; i++) results[i] = Math.pow(i, 1.5); } }); } ex.shutdown(); ex.awaitTermination(1, TimeUnit.MINUTES); long time = System.nanoTime() - start; System.out.printf(\"With four threads it took %.1f ns per pow 1.5%n\", (double) time / results.length); }几乎提高了4倍。盛虱
骂狮淋唐便
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