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/*
* Copyright 2015, Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
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*
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* notice, this list of conditions and the following disclaimer.
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* in the documentation and/or other materials provided with the
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*
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*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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package org.glowroot.agent.shaded.grpc;
import org.glowroot.agent.shaded.google.common.annotations.VisibleForTesting;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.ServiceLoader;
/**
* Provider of managed channels for transport agnostic consumption.
*
* Implementations should not throw. If they do, it may interrupt class loading. If
* exceptions may reasonably occur for implementation-specific reasons, implementations should
* generally handle the exception gracefully and return {@code false} from {@link #isAvailable()}.
*/
@Internal
public abstract class ManagedChannelProvider {
private static final ManagedChannelProvider provider
= load(getCorrectClassLoader());
@VisibleForTesting
static ManagedChannelProvider load(ClassLoader classLoader) {
ServiceLoader providers
= ServiceLoader.load(ManagedChannelProvider.class, classLoader);
List list = new ArrayList();
for (ManagedChannelProvider current : providers) {
if (!current.isAvailable()) {
continue;
}
list.add(current);
}
if (list.isEmpty()) {
return null;
} else {
return Collections.max(list, new Comparator() {
@Override
public int compare(ManagedChannelProvider f1, ManagedChannelProvider f2) {
return f1.priority() - f2.priority();
}
});
}
}
/**
* Returns the ClassLoader-wide default channel.
*
* @throws ProviderNotFoundException if no provider is available
*/
public static ManagedChannelProvider provider() {
if (provider == null) {
throw new ProviderNotFoundException("No functional channel service provider found. "
+ "Try adding a dependency on the grpc-okhttp or grpc-netty artifact");
}
return provider;
}
private static ClassLoader getCorrectClassLoader() {
if (isAndroid()) {
// When android:sharedUserId or android:process is used, Android will setup a dummy
// ClassLoader for the thread context (http://stackoverflow.com/questions/13407006),
// instead of letting users to manually set context class loader, we choose the
// correct class loader here.
return ManagedChannelProvider.class.getClassLoader();
}
return Thread.currentThread().getContextClassLoader();
}
protected static boolean isAndroid() {
try {
Class.forName("android.app.Application", /*initialize=*/ false, null);
return true;
} catch (Exception e) {
// If Application isn't loaded, it might as well not be Android.
return false;
}
}
/**
* Whether this provider is available for use, taking the current environment into consideration.
* If {@code false}, no other methods are safe to be called.
*/
protected abstract boolean isAvailable();
/**
* A priority, from 0 to 10 that this provider should be used, taking the current environment into
* consideration. 5 should be considered the default, and then tweaked based on environment
* detection. A priority of 0 does not imply that the provider wouldn't work; just that it should
* be last in line.
*/
protected abstract int priority();
/**
* Creates a new builder with the given host and port.
*/
protected abstract ManagedChannelBuilder builderForAddress(String name, int port);
/**
* Creates a new builder with the given target URI.
*/
@ExperimentalApi
protected abstract ManagedChannelBuilder builderForTarget(String target);
public static final class ProviderNotFoundException extends RuntimeException {
public ProviderNotFoundException(String msg) {
super(msg);
}
}
}