/*
 * 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
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 */
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 UnsatisfiedLinkError in unexpected places. 

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

    public static void tryToInitializeJVM() {
    }
}