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/* |
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* @test |
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* @synopsis multiple threads using a single builtin lock |
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*/ |
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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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*/ |
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|
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import java.util.concurrent.*; |
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import java.util.concurrent.locks.*; |
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import java.util.concurrent.atomic.*; |
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import java.util.*; |
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|
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public final class NoopSpinLockLoops { |
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static final ExecutorService pool = Executors.newCachedThreadPool(); |
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static final LoopHelpers.SimpleRandom rng = new LoopHelpers.SimpleRandom(); |
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static boolean print = false; |
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static int iters = 20000000; |
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|
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public static void main(String[] args) throws Exception { |
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int maxThreads = 100; |
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if (args.length > 0) |
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maxThreads = Integer.parseInt(args[0]); |
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|
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new ReentrantLockLoop(1).test(); |
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new ReentrantLockLoop(1).test(); |
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print = true; |
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|
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int k = 1; |
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for (int i = 1; i <= maxThreads;) { |
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System.out.print("Threads: " + i); |
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new ReentrantLockLoop(i).test(); |
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Thread.sleep(100); |
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if (i == k) { |
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k = i << 1; |
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i = i + (i >>> 1); |
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} |
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else |
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i = k; |
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} |
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pool.shutdown(); |
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} |
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|
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static final class ReentrantLockLoop implements Runnable { |
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private int v = rng.next(); |
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private volatile int result = 17; |
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private final LoopHelpers.BarrierTimer timer = new LoopHelpers.BarrierTimer(); |
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private final CyclicBarrier barrier; |
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private final int nthreads; |
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private volatile int readBarrier; |
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private final AtomicInteger spinlock = new AtomicInteger(); |
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ReentrantLockLoop(int nthreads) { |
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this.nthreads = nthreads; |
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barrier = new CyclicBarrier(nthreads+1, timer); |
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} |
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|
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final void test() throws Exception { |
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for (int i = 0; i < nthreads; ++i) |
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pool.execute(this); |
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barrier.await(); |
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barrier.await(); |
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if (print) { |
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long time = timer.getTime(); |
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long tpi = time / ((long)iters * nthreads); |
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System.out.print("\t" + LoopHelpers.rightJustify(tpi) + " ns per lock"); |
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double secs = (double)(time) / 1000000000.0; |
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System.out.println("\t " + secs + "s run time"); |
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} |
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|
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int r = result; |
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if (r == 0) // avoid overoptimization |
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System.out.println("useless result: " + r); |
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} |
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|
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public final void run() { |
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final AtomicInteger lock = this.spinlock; |
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try { |
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barrier.await(); |
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int sum = v + 1; |
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int x = sum + 1; |
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int n = iters; |
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while (n-- > 0) { |
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while (!lock.compareAndSet(0, 1)) ; |
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x = LoopHelpers.compute4(x); |
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lock.set(0); |
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if ((x += readBarrier) == 0) |
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++readBarrier; |
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|
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sum += x; |
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} |
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barrier.await(); |
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result += sum; |
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} |
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catch (Exception ie) { |
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return; |
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} |
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} |
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} |
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|
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} |
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|
