code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.loops;
  
  /*
   * Written by Doug Lea with assistance from members of JCP JSR-166
   * Expert Group and released to the public domain, as explained at
   * http://creativecommons.org/licenses/publicdomain
   */
  /*
   * @test
   * @summary basic safety and liveness of ReentrantLocks, and other locks based on them
   */
  
  import java.util.concurrent.*;
  import java.util.concurrent.locks.*;
  import java.util.*;
  
  public final class CheckedLockLoops {
      static final ExecutorService pool = Executors.newCachedThreadPool();
      static final LoopHelpers.SimpleRandom rng = new LoopHelpers.SimpleRandom();
      static boolean print = false;
      static boolean doBuiltin = true;
  
      public static void main(String[] args) throws Exception {
          int maxThreads = 100;
          int iters = 2000000;
          if (args.length > 0)
              maxThreads = Integer.parseInt(args[0]);
          rng.setSeed(3122688L);
          warmup(iters);
          runTest(maxThreads, iters);
          pool.shutdown();
      }
  
      static void runTest(int maxThreads, int iters) throws Exception {
          print = true;
          int k = 1;
          for (int i = 1; i <= maxThreads;) {
              System.out.println("Threads:" + i);
              oneTest(i, iters / i);
              if (i == k) {
                  k = i << 1;
                  i = i + (i >>> 1);
              }
              else
                  i = k;
          }
      }
  
      static void warmup(int iters) throws Exception {
          print = false;
          System.out.println("Warmup...");
          oneTest(1, iters);
          oneTest(2, iters / 2);
      }
  
      static void oneTest(int nthreads, int iters) throws Exception {
          int fairIters = (nthreads <= 1) ? iters : iters/20;
          int v = rng.next();
  
          if (print)
              System.out.print("NoLock (1 thread)     ");
          new NoLockLoop().test(v, 1, iters * nthreads);
          Thread.sleep(10);
  
          if (print)
              System.out.print("ReentrantLock         ");
          new ReentrantLockLoop().test(v, nthreads, iters);
          Thread.sleep(10);
  
          if (print)
              System.out.print("FairReentrantLock     ");
          new FairReentrantLockLoop().test(v, nthreads, fairIters);
          Thread.sleep(10);
  
          if (doBuiltin) {
              if (print)
                  System.out.print("builtin lock          ");
              new BuiltinLockLoop().test(v, nthreads, fairIters);
              Thread.sleep(10);
          }
  
          if (print)
              System.out.print("Mutex                 ");
          new MutexLoop().test(v, nthreads, iters);
          Thread.sleep(10);
  
          if (print)
              System.out.print("LongMutex             ");
          new LongMutexLoop().test(v, nthreads, iters);
          Thread.sleep(10);
  
          if (print)
              System.out.print("Semaphore             ");
          new SemaphoreLoop().test(v, nthreads, iters);
          Thread.sleep(10);
  
          if (print)
              System.out.print("FairSemaphore         ");
          new FairSemaphoreLoop().test(v, nthreads, fairIters);
          Thread.sleep(10);
  
          if (print)
              System.out.print("ReentrantWriteLock    ");
          new ReentrantWriteLockLoop().test(v, nthreads, iters);
          Thread.sleep(10);
  
          if (print)
              System.out.print("FairRWriteLock         ");
          new FairReentrantWriteLockLoop().test(v, nthreads, fairIters);
          Thread.sleep(10);
  
          if (print)
              System.out.print("ReentrantReadWriteLock");
          new ReentrantReadWriteLockLoop().test(v, nthreads, iters);
          Thread.sleep(10);
  
          if (print)
              System.out.print("FairRReadWriteLock     ");
          new FairReentrantReadWriteLockLoop().test(v, nthreads, fairIters);
          Thread.sleep(10);
      }
  
      static abstract class LockLoop implements Runnable {
          int value;
          int checkValue;
          int iters;
          volatile int result;
          volatile int failures;
          final LoopHelpers.BarrierTimer timer = new LoopHelpers.BarrierTimer();
          CyclicBarrier barrier;
  
          final int setValue(int v) {
              checkValue = v ^ 0x55555555;
              value = v;
              return v;
          }
  
          final int getValue() {
              int v = value;
              if (checkValue != ~(v ^ 0xAAAAAAAA))
                  ++failures;
              return v;
          }
  
          final void test(int initialValue, int nthreads, int iters) throws Exception {
              setValue(initialValue);
              this.iters = iters;
              barrier = new CyclicBarrier(nthreads+1, timer);
              for (int i = 0; i < nthreads; ++i)
                  pool.execute(this);
              barrier.await();
              barrier.await();
              long time = timer.getTime();
              if (print) {
                  long tpi = time / (iters * nthreads);
                  System.out.print("\t" + LoopHelpers.rightJustify(tpi) + " ns per update");
                  System.out.println();
              }
  
              if (result == 0) // avoid overoptimization
                  System.out.println("useless result: " + result);
              if (failures != 0)
                  throw new Error("lock protection failure");
          }
  
          abstract int loop(int n);
          public final void run() {
              try {
                  barrier.await();
                  result += loop(iters);
                  barrier.await();
              }
              catch (Exception ie) {
                  return;
              }
          }
  
      }
  
      private static class NoLockLoop extends LockLoop {
          private volatile int readBarrier;
          final int loop(int n) {
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  int r1 = readBarrier;
                  x = setValue(LoopHelpers.compute1(getValue()));
                  int r2 = readBarrier;
                  if (r1 == r2 && x == r1)
                      ++readBarrier;
                  sum += LoopHelpers.compute2(x);
              }
              return sum;
          }
      }
  
      private static class BuiltinLockLoop extends LockLoop {
          final int loop(int n) {
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  synchronized(this) {
                      x = setValue(LoopHelpers.compute1(getValue()));
                  }
                  sum += LoopHelpers.compute2(x);
              }
              return sum;
          }
      }
  
      private static class ReentrantLockLoop extends LockLoop {
          final private ReentrantLock lock = new ReentrantLock();
          final int loop(int n) {
              final ReentrantLock lock = this.lock;
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  lock.lock();
                  try {
                      x = setValue(LoopHelpers.compute1(getValue()));
                  }
                  finally {
                      lock.unlock();
                  }
                  sum += LoopHelpers.compute2(x);
              }
              return sum;
          }
      }
  
      private static class MutexLoop extends LockLoop {
          final private Mutex lock = new Mutex();
          final int loop(int n) {
              final Mutex lock = this.lock;
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  lock.lock();
                  try {
                      x = setValue(LoopHelpers.compute1(getValue()));
                  }
                  finally {
                      lock.unlock();
                  }
                  sum += LoopHelpers.compute2(x);
              }
              return sum;
          }
      }
  
      private static class LongMutexLoop extends LockLoop {
          final private LongMutex lock = new LongMutex();
          final int loop(int n) {
              final LongMutex lock = this.lock;
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  lock.lock();
                  try {
                      x = setValue(LoopHelpers.compute1(getValue()));
                  }
                  finally {
                      lock.unlock();
                  }
                  sum += LoopHelpers.compute2(x);
              }
              return sum;
          }
      }
  
      private static class FairReentrantLockLoop extends LockLoop {
          final private ReentrantLock lock = new ReentrantLock(true);
          final int loop(int n) {
              final ReentrantLock lock = this.lock;
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  lock.lock();
                  try {
                      x = setValue(LoopHelpers.compute1(getValue()));
                  }
                  finally {
                      lock.unlock();
                  }
                  sum += LoopHelpers.compute2(x);
              }
              return sum;
          }
      }
  
      private static class ReentrantWriteLockLoop extends LockLoop {
          final private Lock lock = new ReentrantReadWriteLock().writeLock();
          final int loop(int n) {
              final Lock lock = this.lock;
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  lock.lock();
                  try {
                      x = setValue(LoopHelpers.compute1(getValue()));
                  }
                  finally {
                      lock.unlock();
                  }
                  sum += LoopHelpers.compute2(x);
              }
              return sum;
          }
      }
  
      private static class FairReentrantWriteLockLoop extends LockLoop {
          final Lock lock = new ReentrantReadWriteLock(true).writeLock();
          final int loop(int n) {
              final Lock lock = this.lock;
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  lock.lock();
                  try {
                      x = setValue(LoopHelpers.compute1(getValue()));
                  }
                  finally {
                      lock.unlock();
                  }
                  sum += LoopHelpers.compute2(x);
              }
              return sum;
          }
      }
  
      private static class SemaphoreLoop extends LockLoop {
          final private Semaphore sem = new Semaphore(1, false);
          final int loop(int n) {
              final Semaphore sem = this.sem;
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  sem.acquireUninterruptibly();
                  try {
                      x = setValue(LoopHelpers.compute1(getValue()));
                  }
                  finally {
                      sem.release();
                  }
                  sum += LoopHelpers.compute2(x);
              }
              return sum;
          }
      }
      private static class FairSemaphoreLoop extends LockLoop {
          final private Semaphore sem = new Semaphore(1, true);
          final int loop(int n) {
              final Semaphore sem = this.sem;
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  sem.acquireUninterruptibly();
                  try {
                      x = setValue(LoopHelpers.compute1(getValue()));
                  }
                  finally {
                      sem.release();
                  }
                  sum += LoopHelpers.compute2(x);
              }
              return sum;
          }
      }
  
      private static class ReentrantReadWriteLockLoop extends LockLoop {
          final private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
          final int loop(int n) {
              final Lock rlock = lock.readLock();
              final Lock wlock = lock.writeLock();
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  if ((n & 16) != 0) {
                      rlock.lock();
                      try {
                          x = LoopHelpers.compute1(getValue());
                          x = LoopHelpers.compute2(x);
                      }
                      finally {
                          rlock.unlock();
                      }
                  }
                  else {
                      wlock.lock();
                      try {
                          setValue(x);
                      }
                      finally {
                          wlock.unlock();
                      }
                      sum += LoopHelpers.compute2(x);
                  }
              }
              return sum;
          }
  
      }
  
  
      private static class FairReentrantReadWriteLockLoop extends LockLoop {
          final private ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
          final int loop(int n) {
              final Lock rlock = lock.readLock();
              final Lock wlock = lock.writeLock();
              int sum = 0;
              int x = 0;
              while (n-- > 0) {
                  if ((n & 16) != 0) {
                      rlock.lock();
                      try {
                          x = LoopHelpers.compute1(getValue());
                          x = LoopHelpers.compute2(x);
                      }
                      finally {
                          rlock.unlock();
                      }
                  }
                  else {
                      wlock.lock();
                      try {
                          setValue(x);
                      }
                      finally {
                          wlock.unlock();
                      }
                      sum += LoopHelpers.compute2(x);
                  }
              }
              return sum;
          }
  
      }
  }
  