GetThreadPoolAction.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.sun.jini.thread;

import java.security.Permission;
import java.security.PrivilegedAction;

/**
 * Provides security-checked access to internal thread pools as a
 * java.security.PrivilegedAction, to be used conveniently with an
 * AccessController.doPrivileged or Security.doPrivileged.
 *
 * There are two internal thread pools: one of threads in the system
 * thread group, for executing tasks to be guarded by the security
 * policy for the system thread group, and one of threads in a
 * non-system thread group, for executing tasks with user code that
 * should not be restricted by that policy.
 *
 * If there is a security manager, the run method will check the
 * ThreadPoolPermission for the requested thread pool.  If used with a
 * doPrivileged (the typical case), then only the protection domain of
 * the immediate caller of the doPrivileged needs the permission.
 *
 * The thread pools execute an action in a thread without the security
 * context in which the execute method was invoked, without any
 * subject, and with the system class loader as the context class
 * loader.  Actions are expected to complete with the same context
 * class loader and other thread-specific state (such as priority)
 * that they were started with.
 *
 * @author Sun Microsystems, Inc.
 **/
public final class GetThreadPoolAction implements PrivilegedAction {

    /** pool of threads for executing tasks in system thread group */
    private static final ThreadPool systemThreadPool =
	new ThreadPool(NewThreadAction.systemThreadGroup);

    /** pool of threads for executing tasks with user code */
    private static final ThreadPool userThreadPool =
	new ThreadPool(NewThreadAction.userThreadGroup);

    private static final Permission getSystemThreadPoolPermission =
	new ThreadPoolPermission("getSystemThreadPool");
    private static final Permission getUserThreadPoolPermission =
	new ThreadPoolPermission("getUserThreadPool");

    private final boolean user;

    /**
     * Creates an action that will obtain an internal thread pool.
     * When run, this action verifies that the current access control
     * context has permission to access the thread group used by the
     * indicated pool.
     *
     * @param	user if true, will obtain the non-system thread group
     * pool for executing user code; if false, will obtain the system
     * thread group pool
     */
    public GetThreadPoolAction(boolean user) {
	this.user = user;
    }

    public Object run() {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	    sm.checkPermission(user ? getUserThreadPoolPermission :
			       getSystemThreadPoolPermission);
	}
	return user ? userThreadPool : systemThreadPool;
    }
}