Carl Mastrangelo | 416b745 | 2015-09-09 15:56:47 -0700 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2015, Google Inc. All rights reserved. |
| 3 | * |
| 4 | * Redistribution and use in source and binary forms, with or without |
| 5 | * modification, are permitted provided that the following conditions are |
| 6 | * met: |
| 7 | * |
| 8 | * * Redistributions of source code must retain the above copyright |
| 9 | * notice, this list of conditions and the following disclaimer. |
| 10 | * * Redistributions in binary form must reproduce the above |
| 11 | * copyright notice, this list of conditions and the following disclaimer |
| 12 | * in the documentation and/or other materials provided with the |
| 13 | * distribution. |
| 14 | * |
| 15 | * * Neither the name of Google Inc. nor the names of its |
| 16 | * contributors may be used to endorse or promote products derived from |
| 17 | * this software without specific prior written permission. |
| 18 | * |
| 19 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| 20 | * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| 21 | * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| 22 | * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| 23 | * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| 24 | * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| 25 | * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 26 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 27 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 28 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| 29 | * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| 30 | */ |
| 31 | |
| 32 | package io.grpc; |
| 33 | |
| 34 | import com.google.common.annotations.VisibleForTesting; |
| 35 | |
| 36 | import io.grpc.ManagedChannelProvider.ProviderNotFoundException; |
| 37 | |
| 38 | import java.util.ServiceLoader; |
| 39 | |
| 40 | /** |
| 41 | * Provider of servers for transport agnostic consumption. |
| 42 | * |
| 43 | * <p>Implementations <em>should not</em> throw. If they do, it may interrupt class loading. If |
| 44 | * exceptions may reasonably occur for implementation-specific reasons, implementations should |
| 45 | * generally handle the exception gracefully and return {@code false} from {@link #isAvailable()}. |
| 46 | */ |
| 47 | @Internal |
| 48 | public abstract class ServerProvider { |
| 49 | private static final ServerProvider provider = |
| 50 | load(Thread.currentThread().getContextClassLoader()); |
| 51 | |
| 52 | @VisibleForTesting |
| 53 | static final ServerProvider load(ClassLoader cl) { |
| 54 | ServiceLoader<ServerProvider> providers = ServiceLoader.load(ServerProvider.class, cl); |
| 55 | ServerProvider best = null; |
| 56 | |
| 57 | for (ServerProvider current : providers) { |
| 58 | if (!current.isAvailable()) { |
| 59 | continue; |
| 60 | } else if (best == null) { |
| 61 | best = current; |
| 62 | } else if (current.priority() > best.priority()) { |
| 63 | best = current; |
| 64 | } |
| 65 | } |
| 66 | return best; |
| 67 | } |
| 68 | |
| 69 | /** |
| 70 | * Returns the ClassLoader-wide default server. |
| 71 | * |
| 72 | * @throws ProviderNotFoundException if no provider is available |
| 73 | */ |
| 74 | public static ServerProvider provider() { |
| 75 | if (provider == null) { |
| 76 | throw new ProviderNotFoundException("No functional server found. " |
| 77 | + "Try adding a dependency on the grpc-netty artifact"); |
| 78 | } |
| 79 | return provider; |
| 80 | } |
| 81 | |
| 82 | /** |
| 83 | * Whether this provider is available for use, taking the current environment into consideration. |
| 84 | * If {@code false}, no other methods are safe to be called. |
| 85 | */ |
| 86 | protected abstract boolean isAvailable(); |
| 87 | |
| 88 | /** |
| 89 | * A priority, from 0 to 10 that this provider should be used, taking the current environment into |
| 90 | * consideration. 5 should be considered the default, and then tweaked based on environment |
| 91 | * detection. A priority of 0 does not imply that the provider wouldn't work; just that it should |
| 92 | * be last in line. |
| 93 | */ |
| 94 | protected abstract int priority(); |
| 95 | |
| 96 | /** |
| 97 | * Creates a new builder with the given port. |
| 98 | */ |
| 99 | protected abstract ServerBuilder<?> builderForPort(int port); |
| 100 | } |
| 101 | |