1 /*
   2  * Copyright (c) 2014, 2015, 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.util.Formatter;
  26 import java.util.Iterator;
  27 import java.util.ServiceConfigurationError;
  28 import java.util.ServiceLoader;
  29 
  30 /**
  31  * A mechanism for accessing service providers via JVMCI.
  32  */
  33 public final class Services {
  34 
  35     private Services() {
  36     }
  37 
  38     /**
  39      * Gets an {@link Iterable} of the JVMCI providers available for a given service.
  40      */
  41     public static <S> Iterable<S> load(Class<S> service) {
  42         return ServiceLoader.load(service);
  43     }
  44 
  45     /**
  46      * Gets the JVMCI provider for a given service for which at most one provider must be available.
  47      *
  48      * @param service the service whose provider is being requested
  49      * @param required specifies if an {@link InternalError} should be thrown if no provider of
  50      *            {@code service} is available
  51      */
  52     public static <S> S loadSingle(Class<S> service, boolean required) {
  53         Iterable<S> providers = ServiceLoader.load(service);
  54         S singleProvider = null;
  55         try {
  56             for (Iterator<S> it = providers.iterator(); it.hasNext();) {
  57                 singleProvider = it.next();
  58                 if (it.hasNext()) {
  59                     throw new InternalError(String.format("Multiple %s providers found", service.getName()));
  60                 }
  61             }
  62         } catch (ServiceConfigurationError e) {
  63             // If the service is required we will bail out below.
  64         }
  65         if (singleProvider == null && required) {
  66             String javaHome = System.getProperty("java.home");
  67             String vmName = System.getProperty("java.vm.name");
  68             Formatter errorMessage = new Formatter();
  69             errorMessage.format("The VM does not expose required service %s.%n", service.getName());
  70             errorMessage.format("Currently used Java home directory is %s.%n", javaHome);
  71             errorMessage.format("Currently used VM configuration is: %s", vmName);
  72             throw new UnsupportedOperationException(errorMessage.toString());
  73         }
  74         return singleProvider;
  75     }
  76 }