8253280: Use class name as class loading lock

src/java.base/share/classes/java/lang/ClassLoader.java

@@ -661,7 +661,7 @@ final Class<?> loadClass(Module module, String name) {
     protected Object getClassLoadingLock(String className) {
         Object lock = this;
         if (parallelLockMap != null) {
-            Object newLock = new Object();
+            Object newLock = new String(className);
             lock = parallelLockMap.putIfAbsent(className, newLock);
             if (lock == null) {
                 lock = newLock;

src/java.management/share/classes/java/lang/management/LockInfo.java

@@ -57,6 +57,24 @@ public class LockInfo {
 
     private String className;
     private int    identityHashCode;
+    private String stringValue;
+
+    /**
+     * Constructs a {@code LockInfo} object.
+     *
+     * @param className the fully qualified name of the class of the lock object.
+     * @param identityHashCode the {@link System#identityHashCode
+     *                         identity hash code} of the lock object.
+     * @param stringValue the string value of the lock object.
+     */
+    public LockInfo(String className, int identityHashCode, String stringValue) {
+        if (className == null) {
+            throw new NullPointerException("Parameter className cannot be null");
+        }
+        this.className = className;
+        this.identityHashCode = identityHashCode;
+        this.stringValue = stringValue;
+    }
 
     /**
      * Constructs a {@code LockInfo} object.
@@ -77,6 +95,7 @@ public LockInfo(String className, int identityHashCode) {
      * package-private constructors
      */
     LockInfo(Object lock) {
+        this.stringValue = String.valueOf(lock);
         this.className = lock.getClass().getName();
         this.identityHashCode = System.identityHashCode(lock);
     }
@@ -90,6 +109,15 @@ public String getClassName() {
         return className;
     }
 
+    /**
+     * Returns the string value of lock object.
+     *
+     * @return the string value of lock object.
+     */
+    public String getStringValue() {
+        return stringValue;
+    }
+
     /**
      * Returns the identity hash code of the lock object
      * returned from the {@link System#identityHashCode} method.

src/java.management/share/classes/java/lang/management/MonitorInfo.java

@@ -76,6 +76,39 @@ public MonitorInfo(String className,
         this.stackFrame = stackFrame;
     }
 
+    /**
+     * Construct a {@code MonitorInfo} object.
+     *
+     * @param className the fully qualified name of the class of the lock object.
+     * @param identityHashCode the {@link System#identityHashCode
+     *                         identity hash code} of the lock object.
+     * @param stringValue the string value of the lock object.
+     * @param stackDepth the depth in the stack trace where the object monitor
+     *                   was locked.
+     * @param stackFrame the stack frame that locked the object monitor.
+     * @throws IllegalArgumentException if
+     *    {@code stackDepth} ≥ 0 but {@code stackFrame} is {@code null},
+     *    or {@code stackDepth} < 0 but {@code stackFrame} is not
+     *       {@code null}.
+     */
+    public MonitorInfo(String className,
+                       int identityHashCode,
+                       String stringValue,
+                       int stackDepth,
+                       StackTraceElement stackFrame) {
+        super(className, identityHashCode, stringValue);
+        if (stackDepth >= 0 && stackFrame == null) {
+            throw new IllegalArgumentException("Parameter stackDepth is " +
+                stackDepth + " but stackFrame is null");
+        }
+        if (stackDepth < 0 && stackFrame != null) {
+            throw new IllegalArgumentException("Parameter stackDepth is " +
+                stackDepth + " but stackFrame is not null");
+        }
+        this.stackDepth = stackDepth;
+        this.stackFrame = stackFrame;
+    }
+
     /**
      * Returns the depth in the stack trace where the object monitor
      * was locked.  The depth is the index to the {@code StackTraceElement}
@@ -149,10 +182,12 @@ public static MonitorInfo from(CompositeData cd) {
             MonitorInfoCompositeData.validateCompositeData(cd);
             String className = MonitorInfoCompositeData.getClassName(cd);
             int identityHashCode = MonitorInfoCompositeData.getIdentityHashCode(cd);
+            String stringValue = MonitorInfoCompositeData.getStringValue(cd);
             int stackDepth = MonitorInfoCompositeData.getLockedStackDepth(cd);
             StackTraceElement stackFrame = MonitorInfoCompositeData.getLockedStackFrame(cd);
             return new MonitorInfo(className,
                                    identityHashCode,
+                                   stringValue,
                                    stackDepth,
                                    stackFrame);
         }

src/java.management/share/classes/java/lang/management/ThreadInfo.java

@@ -172,11 +172,13 @@ private ThreadInfo(Thread t, int state, Object lockObj, Thread lockOwner,
                 Object lock = monitors[i];
                 String className = lock.getClass().getName();
                 int identityHashCode = System.identityHashCode(lock);
+                String stringValue = String.valueOf(lock);
                 int depth = stackDepths[i];
                 StackTraceElement ste = (depth >= 0 ? stackTrace[depth]
                                                     : null);
                 lockedMonitors[i] = new MonitorInfo(className,
                                                     identityHashCode,
+                                                    stringValue,
                                                     depth,
                                                     ste);
             }

src/java.management/share/classes/sun/management/MonitorInfoCompositeData.java

@@ -62,6 +62,7 @@ protected CompositeData getCompositeData() {
                                              : null;
         // values may be null; can't use Map.of
         Map<String,Object> items = new HashMap<>();
+        items.put(STRING_VALUE,       lock.getStringValue());
         items.put(CLASS_NAME,         lock.getClassName());
         items.put(IDENTITY_HASH_CODE, lock.getIdentityHashCode());
         items.put(LOCKED_STACK_FRAME, steCData);
@@ -75,12 +76,14 @@ protected CompositeData getCompositeData() {
         }
     }
 
+    private static final String STRING_VALUE       = "stringValue";
     private static final String CLASS_NAME         = "className";
     private static final String IDENTITY_HASH_CODE = "identityHashCode";
     private static final String LOCKED_STACK_FRAME = "lockedStackFrame";
     private static final String LOCKED_STACK_DEPTH = "lockedStackDepth";
 
     private static final String[] MONITOR_INFO_ATTRIBUTES = {
+        STRING_VALUE,
         CLASS_NAME,
         IDENTITY_HASH_CODE,
         LOCKED_STACK_FRAME,
@@ -116,6 +119,10 @@ static CompositeType v6CompositeType() {
         return V6_COMPOSITE_TYPE;
     }
 
+    public static String getStringValue(CompositeData cd) {
+        return getString(cd, STRING_VALUE);
+    }
+
     public static String getClassName(CompositeData cd) {
         return getString(cd, CLASS_NAME);
     }