com.google.devtools.build.lib.analysis.TransitiveInfoProviderMapOffsetBased.java Source code

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Here is the source code for com.google.devtools.build.lib.analysis.TransitiveInfoProviderMapOffsetBased.java

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// Copyright 2017 The Bazel Authors. All rights reserved.
//
// 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.google.devtools.build.lib.analysis;

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Interner;
import com.google.devtools.build.lib.concurrent.BlazeInterners;
import java.util.Arrays;
import java.util.Map.Entry;
import javax.annotation.Nullable;
import javax.annotation.concurrent.Immutable;

/**
 * Provides a mapping between a TransitiveInfoProvider class and an instance.
 *
 * <p>This class implements a map where it is expected that a lot of the key sets will be the same.
 * These key sets are shared and an offset table of indices is computed. Each provider map instance
 * thus contains only a reference to the shared offset table, and a plain array of providers.
 */
@Immutable
final class TransitiveInfoProviderMapOffsetBased implements TransitiveInfoProviderMap {
    private static final Interner<OffsetTable> offsetTables = BlazeInterners.newWeakInterner();

    private final OffsetTable offsetTable;
    private final TransitiveInfoProvider[] providers;

    private static final class OffsetTable {
        private final Class<? extends TransitiveInfoProvider>[] providerClasses;
        // Keep a map around to speed up get lookups for larger maps.
        // We make this value lazy to avoid computing for values that end up being thrown away
        // during interning anyway (the majority).
        private volatile ImmutableMap<Class<? extends TransitiveInfoProvider>, Integer> indexMap;

        OffsetTable(Class<? extends TransitiveInfoProvider>[] providerClasses) {
            this.providerClasses = providerClasses;
        }

        private ImmutableMap<Class<? extends TransitiveInfoProvider>, Integer> getIndexMap() {
            if (indexMap == null) {
                synchronized (this) {
                    if (indexMap == null) {
                        ImmutableMap.Builder<Class<? extends TransitiveInfoProvider>, Integer> builder = ImmutableMap
                                .builder();
                        for (int i = 0; i < providerClasses.length; ++i) {
                            builder.put(providerClasses[i], i);
                        }
                        this.indexMap = builder.build();
                    }
                }
            }
            return indexMap;
        }

        int getOffsetForClass(Class effectiveClass) {
            return getIndexMap().getOrDefault(effectiveClass, -1);
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (!(o instanceof OffsetTable)) {
                return false;
            }
            OffsetTable that = (OffsetTable) o;
            return Arrays.equals(this.providerClasses, that.providerClasses);
        }

        @Override
        public int hashCode() {
            return Arrays.hashCode(providerClasses);
        }
    }

    TransitiveInfoProviderMapOffsetBased(
            ImmutableMap<Class<? extends TransitiveInfoProvider>, TransitiveInfoProvider> map) {
        int count = map.size();
        Class<? extends TransitiveInfoProvider>[] providerClasses = new Class[count];
        this.providers = new TransitiveInfoProvider[count];
        int i = 0;
        for (Entry<Class<? extends TransitiveInfoProvider>, TransitiveInfoProvider> entry : map.entrySet()) {
            providerClasses[i] = entry.getKey();
            providers[i] = entry.getValue();
            ++i;
        }
        OffsetTable offsetTable = new OffsetTable(providerClasses);
        this.offsetTable = offsetTables.intern(offsetTable);
    }

    /** Returns the instance for the provided providerClass, or <tt>null</tt> if not present. */
    @Override
    @Nullable
    public <P extends TransitiveInfoProvider> P getProvider(Class<P> providerClass) {
        Class effectiveClass = TransitiveInfoProviderEffectiveClassHelper.get(providerClass);
        int offset = offsetTable.getOffsetForClass(effectiveClass);
        return offset >= 0 ? (P) providers[offset] : null;
    }

    @Override
    public int getProviderCount() {
        return providers.length;
    }

    @Override
    public Class<? extends TransitiveInfoProvider> getProviderClassAt(int i) {
        return offsetTable.providerClasses[i];
    }

    @Override
    public TransitiveInfoProvider getProviderAt(int i) {
        return providers[i];
    }
}