8220248: fix headings in java.util.concurrent

Reviewed-by: martin, jjg

src/java.base/share/classes/java/util/concurrent/ExecutorService.java

@@ -66,7 +66,7 @@ import java.util.List;
  * <p>The {@link Executors} class provides factory methods for the
  * executor services provided in this package.
  *
- * <h3>Usage Examples</h3>
+ * <h2>Usage Examples</h2>
  *
  * Here is a sketch of a network service in which threads in a thread
  * pool service incoming requests. It uses the preconfigured {@link

src/java.base/share/classes/java/util/concurrent/ScheduledExecutorService.java

@@ -65,7 +65,7 @@ package java.util.concurrent;
  * <p>The {@link Executors} class provides convenient factory methods for
  * the ScheduledExecutorService implementations provided in this package.
  *
- * <h3>Usage Example</h3>
+ * <h2>Usage Example</h2>
  *
  * Here is a class with a method that sets up a ScheduledExecutorService
  * to beep every ten seconds for an hour:

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

@@ -104,7 +104,7 @@ import java.util.concurrent.TimeUnit;
  * define a {@code readObject} method that restores this to a known
  * initial state upon deserialization.
  *
- * <h3>Usage</h3>
+ * <h2>Usage</h2>
  *
  * <p>To use this class as the basis of a synchronizer, redefine the
  * following methods, as applicable, by inspecting and/or modifying
@@ -187,7 +187,7 @@ import java.util.concurrent.TimeUnit;
  * {@link java.util.Queue} classes, and {@link LockSupport} blocking
  * support.
  *
- * <h3>Usage Examples</h3>
+ * <h2>Usage Examples</h2>
  *
  * <p>Here is a non-reentrant mutual exclusion lock class that uses
  * the value zero to represent the unlocked state, and one to

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

@@ -138,7 +138,7 @@ import java.util.concurrent.TimeUnit;
  * <p>Except where noted, passing a {@code null} value for any parameter
  * will result in a {@link NullPointerException} being thrown.
  *
- * <h3>Implementation Considerations</h3>
+ * <h2>Implementation Considerations</h2>
  *
  * <p>When waiting upon a {@code Condition}, a &quot;<em>spurious
  * wakeup</em>&quot; is permitted to occur, in

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

@@ -117,7 +117,7 @@ import java.util.concurrent.TimeUnit;
  * parameter will result in a {@link NullPointerException} being
  * thrown.
  *
- * <h3>Memory Synchronization</h3>
+ * <h2>Memory Synchronization</h2>
  *
  * <p>All {@code Lock} implementations <em>must</em> enforce the same
  * memory synchronization semantics as provided by the built-in monitor
@@ -136,7 +136,7 @@ import java.util.concurrent.TimeUnit;
  * locking/unlocking operations, do not require any memory
  * synchronization effects.
  *
- * <h3>Implementation Considerations</h3>
+ * <h2>Implementation Considerations</h2>
  *
  * <p>The three forms of lock acquisition (interruptible,
  * non-interruptible, and timed) may differ in their performance

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

@@ -204,7 +204,7 @@ import jdk.internal.vm.annotation.ReservedStackAccess;
  *   }
  * }}</pre>
  *
- * <h3>Implementation Notes</h3>
+ * <h2>Implementation Notes</h2>
  *
  * <p>This lock supports a maximum of 65535 recursive write locks
  * and 65535 read locks. Attempts to exceed these limits result in