/*

 * Copyright (c) 2016, 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.jfr.internal;

import java.io.IOException;

/**

 * Checks if the running VM supports Flight Recorder.

 *

 * Purpose of this helper class is to detect early and cleanly if the VM has

 * support for Flight Recorder, i.e. not throw {@link UnsatisfiedLinkError} in

 * unexpected places.

 * <p>

 * This is needed so a disabled-jfr.jar can be built for non Oracle JDKs.

 */

public final class JVMSupport {

    private static final String UNSUPPORTED_VM_MESSAGE = "Flight Recorder is not supported on this VM";

    private static final boolean notAvailable = !checkAvailability();

    private static boolean checkAvailability() {

        // set jfr.unsupported.vm to true to test API on an unsupported VM

        try {

            if (SecuritySupport.getBooleanProperty("jfr.unsupported.vm")) {

                return false;

            }

        } catch (NoClassDefFoundError cnfe) {

            // May happen on JDK 8, where jdk.internal.misc.Unsafe can't be found

            return false;

        }

        try {

            // Will typically throw UnsatisfiedLinkError if

            // there is no native implementation

            JVM.getJVM().isAvailable();

            return true;

        } catch (Throwable t) {

            return false;

        }

    }

    public static void ensureWithInternalError() {

        if (notAvailable) {

            throw new InternalError(UNSUPPORTED_VM_MESSAGE);

        }

    }

    public static void ensureWithIOException() throws IOException {

        if (notAvailable) {

            throw new IOException(UNSUPPORTED_VM_MESSAGE);

        }

    }

    public static void ensureWithIllegalStateException() {

        if (notAvailable) {

            throw new IllegalStateException(UNSUPPORTED_VM_MESSAGE);

        }

    }

    public static boolean isNotAvailable() {

        return notAvailable;

    }

}