8200256: java/nio/channels/AsynchronousChannelGroup/Basic.java fails intermittently

Reviewed-by: chegar

src/java.base/share/classes/sun/nio/ch/IOUtil.java

@@ -401,8 +401,17 @@ public class IOUtil {
 
     static native int write1(int fd, byte b) throws IOException;
 
+    /**
+     * Read and discard all bytes.
+     */
     static native boolean drain(int fd) throws IOException;
 
+    /**
+     * Read and discard at most one byte
+     * @return the number of bytes read or IOS_INTERRUPTED
+     */
+    static native int drain1(int fd) throws IOException;
+
     public static native void configureBlocking(FileDescriptor fd,
                                                 boolean blocking)
         throws IOException;