1 /*
   2  * Copyright (c) 2014, 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  */
  23 package jdk.vm.ci.services;
  24 
  25 import java.lang.reflect.Module;
  26 import java.util.Formatter;
  27 import java.util.Iterator;
  28 import java.util.ServiceConfigurationError;
  29 import java.util.ServiceLoader;
  30 
  31 /**
  32  * A mechanism for accessing service providers via JVMCI.
  33  */
  34 public final class Services {
  35 
  36     private Services() {
  37     }
  38 
  39     /**
  40      * Performs any required security checks and dynamic reconfiguration to allow the module of a
  41      * given class to access the classes in the JVMCI module.
  42      *
  43      * Note: This API uses {@link Class} instead of {@link Module} to provide backwards
  44      * compatibility for JVMCI clients compiled against a JDK release earlier than 9.
  45      *
  46      * @param requestor a class requesting access to the JVMCI module for its module
  47      * @throws SecurityException if a security manager is present and it denies
  48      *             {@link JVMCIPermission}
  49      */
  50     public static void exportJVMCITo(Class<?> requestor) {
  51         SecurityManager sm = System.getSecurityManager();
  52         if (sm != null) {
  53             sm.checkPermission(new JVMCIPermission());
  54         }
  55         Module jvmci = Services.class.getModule();
  56         Module requestorModule = requestor.getModule();
  57         if (jvmci != requestorModule) {
  58             for (String pkg : jvmci.getPackages()) {
  59                 // Export all JVMCI packages dynamically instead
  60                 // of requiring a long list of -XaddExports
  61                 // options on the JVM command line.
  62                 if (!jvmci.isExported(pkg, requestorModule)) {
  63                     jvmci.addExports(pkg, requestorModule);
  64                 }
  65             }
  66         }
  67     }
  68 
  69     /**
  70      * Gets an {@link Iterable} of the JVMCI providers available for a given service.
  71      *
  72      * @throws SecurityException if a security manager is present and it denies
  73      *             {@link JVMCIPermission}
  74      */
  75     public static <S> Iterable<S> load(Class<S> service) {
  76         SecurityManager sm = System.getSecurityManager();
  77         if (sm != null) {
  78             sm.checkPermission(new JVMCIPermission());
  79         }
  80         Module jvmci = Services.class.getModule();
  81         jvmci.addUses(service);
  82 
  83         // Restrict JVMCI clients to be on the class path or module path
  84         return ServiceLoader.load(service, ClassLoader.getSystemClassLoader());
  85     }
  86 
  87     /**
  88      * Gets the JVMCI provider for a given service for which at most one provider must be available.
  89      *
  90      * @param service the service whose provider is being requested
  91      * @param required specifies if an {@link InternalError} should be thrown if no provider of
  92      *            {@code service} is available
  93      * @throws SecurityException if a security manager is present and it denies
  94      *             {@link JVMCIPermission}
  95      */
  96     public static <S> S loadSingle(Class<S> service, boolean required) {
  97         SecurityManager sm = System.getSecurityManager();
  98         if (sm != null) {
  99             sm.checkPermission(new JVMCIPermission());
 100         }
 101         Module jvmci = Services.class.getModule();
 102         jvmci.addUses(service);
 103         // Restrict JVMCI clients to be on the class path or module path
 104         Iterable<S> providers = ServiceLoader.load(service, ClassLoader.getSystemClassLoader());
 105         S singleProvider = null;
 106         try {
 107             for (Iterator<S> it = providers.iterator(); it.hasNext();) {
 108                 singleProvider = it.next();
 109                 if (it.hasNext()) {
 110                     throw new InternalError(String.format("Multiple %s providers found", service.getName()));
 111                 }
 112             }
 113         } catch (ServiceConfigurationError e) {
 114             // If the service is required we will bail out below.
 115         }
 116         if (singleProvider == null && required) {
 117             String javaHome = System.getProperty("java.home");
 118             String vmName = System.getProperty("java.vm.name");
 119             Formatter errorMessage = new Formatter();
 120             errorMessage.format("The VM does not expose required service %s.%n", service.getName());
 121             errorMessage.format("Currently used Java home directory is %s.%n", javaHome);
 122             errorMessage.format("Currently used VM configuration is: %s", vmName);
 123             throw new UnsupportedOperationException(errorMessage.toString());
 124         }
 125         return singleProvider;
 126     }
 127 }
--- EOF ---