Use a static synchronized method for allPermissionsPD

Since allPermissionsPD is a static field, a static synchronized
method locks on Class.class, which is the correct approach.

Fixes: eclipse-openj9#20351

Signed-off-by: Babneet Singh <[email protected]>

Author: babsingh

Diff for: jcl/src/java.base/share/classes/java/lang/Class.java

@@ -2491,17 +2491,15 @@ ProtectionDomain getProtectionDomainInternal() {
 	return allPermissionsPD;
 }
 
-private void allocateAllPermissionsPD() {
+private static synchronized void allocateAllPermissionsPD() {
 	/* Synchronization to ensure safe initialization and safe publication of
 	 * allPermissionsPD. This addresses the locking contention on allPermissionsPD
 	 * in getProtectionDomain().
 	 */
-	synchronized(this) {
-		if (allPermissionsPD == null) {
-			Permissions collection = new Permissions();
-			collection.add(SecurityConstants.ALL_PERMISSION);
-			allPermissionsPD = new ProtectionDomain(null, collection);
-		}
+	if (allPermissionsPD == null) {
+		Permissions collection = new Permissions();
+		collection.add(SecurityConstants.ALL_PERMISSION);
+		allPermissionsPD = new ProtectionDomain(null, collection);
 	}
 }