8203629: Produce events in the JDK without a dependency on jdk.jfr

Reviewed-by: mgronlun

src/java.base/share/classes/jdk/internal/event/Event.java

@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) 2018, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package jdk.internal.event;
+
+/**
+ * Base class for events, to be subclassed in order to define events and their
+ * fields.
+ */
+public abstract class Event {
+    /**
+     * Sole constructor, for invocation by subclass constructors, typically
+     * implicit.
+     */
+    protected Event() {
+    }
+
+    /**
+     * Starts the timing of this event.
+     */
+    public void begin() {
+    }
+
+    /**
+     * Ends the timing of this event.
+     *
+     * The {@code end} method must be invoked after the {@code begin} method.
+     */
+    public void end() {
+    }
+
+    /**
+     * Writes the field values, time stamp, and event duration.
+     * <p>
+     * If the event starts with an invocation of the {@code begin} method, but does
+     * not end with an explicit invocation of the {@code end} method, then the event
+     * ends when the {@code commit} method is invoked.
+     */
+    public void commit() {
+    }
+
+    /**
+     * Returns {@code true} if the event is enabled, {@code false} otherwise
+     *
+     * @return {@code true} if event is enabled, {@code false} otherwise
+     */
+    public boolean isEnabled() {
+        return false;
+    }
+
+    /**
+     * Returns {@code true} if the event is enabled and if the duration is within
+     * the threshold for the event, {@code false} otherwise.
+     *
+     * @return {@code true} if the event can be written, {@code false} otherwise
+     */
+    public boolean shouldCommit() {
+        return false;
+    }
+
+    /**
+     * Sets a field value.
+     *
+     * @param index the index of the field to set
+     * @param value value to set, can be {@code null}
+     * @throws UnsupportedOperationException if functionality is not supported
+     * @throws IndexOutOfBoundsException if {@code index} is less than {@code 0} or
+     *         greater than or equal to the number of fields specified for the event
+     */
+    public void set(int index, Object value) {
+    }
+}

src/java.base/share/classes/module-info.java

@@ -136,6 +136,8 @@ module java.base {
         java.security.sasl;
     exports jdk.internal to
         jdk.jfr;
+    exports jdk.internal.event to
+        jdk.jfr;
     exports jdk.internal.jimage to
         jdk.jlink;
     exports jdk.internal.jimage.decompressor to