7146776: deadlock between URLStreamHandler.getHostAddress and file.Handler.openconnection

Reviewed-by: alanb, chegar

src/java.base/share/classes/java/net/URL.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1995, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1995, 2021, 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
@@ -249,7 +249,7 @@ public final class URL implements java.io.Serializable {
      * The host's IP address, used in equals and hashCode.
      * Computed on demand. An uninitialized or unknown hostAddress is null.
      */
-    transient InetAddress hostAddress;
+    private transient InetAddress hostAddress;
 
     /**
      * The URLStreamHandler for this URL.
@@ -809,6 +809,31 @@ public final class URL implements java.io.Serializable {
         }
     }
 
+    /**
+     * Returns the address of the host represented by this URL.
+     * A {@link SecurityException} or an {@link UnknownHostException}
+     * while getting the host address will result in this method returning
+     * {@code null}
+     *
+     * @return an {@link InetAddress} representing the host
+     */
+    synchronized InetAddress getHostAddress() {
+        if (hostAddress != null) {
+            return hostAddress;
+        }
+
+        if (host == null || host.isEmpty()) {
+            return null;
+        }
+        try {
+            hostAddress = InetAddress.getByName(host);
+        } catch (UnknownHostException | SecurityException ex) {
+            return null;
+        }
+        return hostAddress;
+    }
+
+
     /**
      * Gets the query part of this {@code URL}.
      *

src/java.base/share/classes/java/net/URLStreamHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1995, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1995, 2021, 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
@@ -443,23 +443,8 @@ public abstract class URLStreamHandler {
      * IP address.
      * @since 1.3
      */
-    protected synchronized InetAddress getHostAddress(URL u) {
-        if (u.hostAddress != null)
-            return u.hostAddress;
-
-        String host = u.getHost();
-        if (host == null || host.isEmpty()) {
-            return null;
-        } else {
-            try {
-                u.hostAddress = InetAddress.getByName(host);
-            } catch (UnknownHostException ex) {
-                return null;
-            } catch (SecurityException se) {
-                return null;
-            }
-        }
-        return u.hostAddress;
+    protected InetAddress getHostAddress(URL u) {
+        return u.getHostAddress();
     }
 
     /**