/*
 * Copyright (c) 2008, 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 sun.tracing.dtrace;

import java.lang.ref.WeakReference;
import java.lang.ref.ReferenceQueue;
import java.security.Permission;
import java.util.HashSet;

class Activation {
    private SystemResource resource;
    private int referenceCount;

    Activation(String moduleName, DTraceProvider[] providers) {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            Permission perm =
                new RuntimePermission("com.sun.tracing.dtrace.createProvider");
            security.checkPermission(perm);
        }
        referenceCount = providers.length;
        for (DTraceProvider p : providers) {
            p.setActivation(this);
        }
        resource = new SystemResource(
            this, JVM.activate(moduleName, providers));
    }

    void disposeProvider(DTraceProvider p) {
        if (--referenceCount == 0) {
            resource.dispose();
        }
    }
}

The native resource part of an Activation. This holds the native handle. If the user loses a reference to a set of Providers without disposing them, and GC determines the Activation is unreachable, then the next activation or flush call will automatically dispose the unreachable objects The SystemResource instances are creating during activation, and unattached during disposal. When created, they always have a strong reference to them via the resources static member. Explicit dispose calls will unregister the native resource and remove references to the SystemResource object. Absent an explicit dispose, when their associated Activation object becomes garbage, the SystemResource object will be enqueued on the reference queue and disposed at the next call to flush. /**
 * The native resource part of an Activation.
 *
 * This holds the native handle.
 *
 * If the user loses a reference to a set of Providers without disposing them,
 * and GC determines the Activation is unreachable, then the next
 * activation or flush call will automatically dispose the unreachable objects
 *
 * The SystemResource instances are creating during activation, and
 * unattached during disposal.  When created, they always have a
 * strong reference to them via the {@code resources} static member.  Explicit
 * {@code dispose} calls will unregister the native resource and remove
 * references to the SystemResource object.  Absent an explicit dispose,
 * when their associated Activation object becomes garbage, the SystemResource
 * object will be enqueued on the reference queue and disposed at the
 * next call to {@code flush}.
 */
class SystemResource extends WeakReference<Activation> {

    private long handle;

    private static ReferenceQueue<Activation> referenceQueue =
        referenceQueue = new ReferenceQueue<Activation>();
    static HashSet<SystemResource> resources = new HashSet<SystemResource>();

    SystemResource(Activation activation, long handle) {
        super(activation, referenceQueue);
        this.handle = handle;
        flush();
        resources.add(this);
    }

    void dispose() {
        JVM.dispose(handle);
        resources.remove(this);
        handle = 0;
    }

    static void flush() {
        SystemResource resource = null;
        while ((resource = (SystemResource)referenceQueue.poll()) != null) {
            if (resource.handle != 0) {
                resource.dispose();
            }
        }
    }
}