Fixes a livelock in AbstractQueuedSynchronizer

src/java.base/share/classes/java/util/concurrent/locks/AbstractQueuedSynchronizer.java

@@ -832,7 +832,8 @@ public abstract class AbstractQueuedSynchronizer
                 if (q.status < 0) {              // cancelled
                     if ((s == null ? casTail(q, p) : s.casPrev(q, p)) &&
                         q.prev == p) {
-                        p.casNext(q, s);         // OK if fails
+                        if (s != null)
+                            p.casNext(q, s);         // OK if fails
                         if (p.prev == null)
                             signalNext(p);
                     }

test/jdk/java/util/concurrent/tck/SemaphoreTest.java

@@ -33,11 +33,15 @@
  * Pat Fisher, Mike Judd.
  */
 
+import static java.util.concurrent.TimeUnit.MICROSECONDS;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 
 import java.util.Collection;
+import java.util.concurrent.Callable;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executors;
 import java.util.concurrent.Semaphore;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import junit.framework.Test;
 import junit.framework.TestSuite;
@@ -672,4 +676,37 @@ public class SemaphoreTest extends JSR166TestCase {
         assertTrue(s.toString().contains("Permits = -2"));
     }
 
+    /**
+     * test scenario for JDK-8386085
+     */
+    public void testShortTimeoutAcquisition() throws InterruptedException {
+        final int width = Runtime.getRuntime().availableProcessors();
+        try (var pool = Executors.newFixedThreadPool(width)) {
+            // Setup
+            final AtomicBoolean done = new AtomicBoolean(false);
+            final CountDownLatch waitingToRun = new CountDownLatch(width);
+            final Semaphore s = new Semaphore(0);
+            final Callable<Void> c = () -> {
+                waitingToRun.countDown();
+                do {
+                    s.tryAcquire(1, MICROSECONDS); // acquisition storm
+                } while (!done.get());
+                return null;
+            };
+
+            // Task creation
+            for(int i = 0; i < width; ++i)
+                pool.submit(c);
+
+            waitingToRun.await();     // Wait for all threads to have launched their tasks
+            Thread.sleep(3000); // Give the workers a bit of time to run acquisitions
+            s.release(width);         // Hand out permits
+            Thread.sleep(1000); // Give the workers a bit of time to react to the availability of permits
+
+            final int permitsAvailable = s.availablePermits();
+            done.set(true); // Try to make sure that for the successful cases the workers can exit cleanly
+            assertTrue(permitsAvailable < width); // Some permits should've been taken
+        }
+    }
+
 }