JVMCIServiceLocator.java revision 12772:fbb9c8026495 
1/*
2 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23package jdk.vm.ci.services;
24
25import java.util.ArrayList;
26import java.util.List;
27import java.util.ServiceLoader;
28
29import jdk.vm.ci.services.internal.ReflectionAccessJDK;
30
31/**
32 * Service-provider class for the runtime to locate providers of JVMCI services where the latter are
33 * not in packages exported by the JVMCI module. As part of instantiating a
34 * {@link JVMCIServiceLocator}, all JVMCI packages will be opened to the module defining the class
35 * of the instantiated object.
36 *
37 * While the {@link #getProvider(Class)} method can be used directly, it's usually easier to use
38 * {@link #getProviders(Class)}.
39 */
40public abstract class JVMCIServiceLocator {
41
42    private static Void checkPermission() {
43        SecurityManager sm = System.getSecurityManager();
44        if (sm != null) {
45            sm.checkPermission(new JVMCIPermission());
46        }
47        return null;
48    }
49
50    @SuppressWarnings("unused")
51    private JVMCIServiceLocator(Void ignore) {
52    }
53
54    /**
55     * Creates a capability for accessing JVMCI. Once successfully instantiated, JVMCI opens all its
56     * packages to the module defining the type of this object.
57     *
58     * @throws SecurityException if a security manager has been installed and it denies
59     *             {@link JVMCIPermission}
60     */
61    protected JVMCIServiceLocator() {
62        this(checkPermission());
63        Services.checkJVMCIEnabled();
64        ReflectionAccessJDK.openJVMCITo(getClass());
65    }
66
67    /**
68     * Gets the provider of the service defined by {@code service} or {@code null} if this object
69     * does not have a provider for {@code service}.
70     */
71    protected abstract <S> S getProvider(Class<S> service);
72
73    /**
74     * Gets the providers of the service defined by {@code service} by querying the available
75     * {@link JVMCIServiceLocator} providers.
76     *
77     * @throws SecurityException if a security manager is present and it denies
78     *             {@link JVMCIPermission}
79     */
80    public static <S> List<S> getProviders(Class<S> service) {
81        Services.checkJVMCIEnabled();
82        SecurityManager sm = System.getSecurityManager();
83        if (sm != null) {
84            sm.checkPermission(new JVMCIPermission());
85        }
86        List<S> providers = new ArrayList<>();
87        for (JVMCIServiceLocator access : ServiceLoader.load(JVMCIServiceLocator.class, ClassLoader.getSystemClassLoader())) {
88            S provider = access.getProvider(service);
89            if (provider != null) {
90                providers.add(provider);
91            }
92        }
93        return providers;
94    }
95}
96