8238566: java.security.Provider$Service.supportsParameter() is racy

Use double-checked-locking pattern inside the hasKeyAttributes() method

Reviewed-by: xuelei

Author: Valerie Peng

src/java.base/share/classes/java/security/Provider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1996, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1996, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -1925,28 +1925,31 @@ private boolean hasKeyAttributes() {
             Boolean b = hasKeyAttributes;
             if (b == null) {
                 synchronized (this) {
-                    String s;
-                    s = getAttribute("SupportedKeyFormats");
-                    if (s != null) {
-                        supportedFormats = s.split("\\|");
-                    }
-                    s = getAttribute("SupportedKeyClasses");
-                    if (s != null) {
-                        String[] classNames = s.split("\\|");
-                        List<Class<?>> classList =
-                            new ArrayList<>(classNames.length);
-                        for (String className : classNames) {
-                            Class<?> clazz = getKeyClass(className);
-                            if (clazz != null) {
-                                classList.add(clazz);
+                    b = hasKeyAttributes;
+                    if (b == null) {
+                        String s;
+                        s = getAttribute("SupportedKeyFormats");
+                        if (s != null) {
+                            supportedFormats = s.split("\\|");
+                        }
+                        s = getAttribute("SupportedKeyClasses");
+                        if (s != null) {
+                            String[] classNames = s.split("\\|");
+                            List<Class<?>> classList =
+                                new ArrayList<>(classNames.length);
+                            for (String className : classNames) {
+                                Class<?> clazz = getKeyClass(className);
+                                if (clazz != null) {
+                                    classList.add(clazz);
+                                }
                             }
+                            supportedClasses = classList.toArray(CLASS0);
                         }
-                        supportedClasses = classList.toArray(CLASS0);
+                        boolean bool = (supportedFormats != null)
+                            || (supportedClasses != null);
+                        b = Boolean.valueOf(bool);
+                        hasKeyAttributes = b;
                     }
-                    boolean bool = (supportedFormats != null)
-                        || (supportedClasses != null);
-                    b = Boolean.valueOf(bool);
-                    hasKeyAttributes = b;
                 }
             }
             return b.booleanValue();