com.facebook.buck.util.ClassLoaderCache.java Source code

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Here is the source code for com.facebook.buck.util.ClassLoaderCache.java

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/*
 * Copyright 2015-present Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License. You may obtain
 * a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package com.facebook.buck.util;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.ImmutableList;

import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;

import javax.annotation.Nullable;

/**
 * Maintain a cache mapping class paths to class loaders that load from these class paths.  The
 * class loaders remain active until ClassLoaderCache itself is unloaded.
 */
public final class ClassLoaderCache implements AutoCloseable {

    private final Map<ClassLoader, Map<ImmutableList<URL>, ClassLoader>> cache = new HashMap<>();

    private int referenceCount = 1;

    private synchronized Map<ImmutableList<URL>, ClassLoader> getCacheForParent(
            @Nullable ClassLoader parentClassLoader) {
        Map<ImmutableList<URL>, ClassLoader> cacheForParent = cache.get(parentClassLoader);

        if (cacheForParent == null) {
            cacheForParent = new HashMap<>();
            cache.put(parentClassLoader, cacheForParent);
        }

        return cacheForParent;
    }

    public synchronized ClassLoader getClassLoaderForClassPath(@Nullable ClassLoader parentClassLoader,
            ImmutableList<URL> classPath) {

        Map<ImmutableList<URL>, ClassLoader> cacheForParent = getCacheForParent(parentClassLoader);

        ClassLoader classLoader = cacheForParent.get(classPath);
        if (classLoader == null) {
            URL[] urls = classPath.toArray(new URL[classPath.size()]);
            classLoader = new URLClassLoader(urls, parentClassLoader);
            cacheForParent.put(classPath, classLoader);
        }

        return classLoader;
    }

    @VisibleForTesting
    public synchronized void injectClassLoader(@Nullable ClassLoader parentClassLoader,
            ImmutableList<URL> classPath, ClassLoader injectedClassLoader) {
        Map<ImmutableList<URL>, ClassLoader> cacheForParent = getCacheForParent(parentClassLoader);

        cacheForParent.put(classPath, injectedClassLoader);
    }

    public synchronized ClassLoaderCache addRef() {
        referenceCount += 1;
        return this;
    }

    @Override
    public synchronized void close() throws IOException {
        if (referenceCount > 1) {
            referenceCount -= 1;
            return;
        }

        Optional<IOException> caughtEx = Optional.empty();

        for (Map<ImmutableList<URL>, ClassLoader> cacheForParent : cache.values()) {
            for (ClassLoader cl : cacheForParent.values()) {
                try {
                    if (cl instanceof URLClassLoader) {
                        ((URLClassLoader) cl).close();
                    }
                } catch (IOException ex) {
                    if (caughtEx.isPresent()) {
                        caughtEx.get().addSuppressed(ex);
                    } else {
                        caughtEx = Optional.of(ex);
                    }
                }
            }
        }

        if (caughtEx.isPresent()) {
            throw caughtEx.get();
        }
    }
}