com.google.gerrit.server.query.AndSource.java Source code

Introduction

Here is the source code for com.google.gerrit.server.query.AndSource.java

Source

// Copyright (C) 2016 The Android Open Source Project
//
// 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.gerrit.server.query;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.common.base.Throwables;
import com.google.common.collect.FluentIterable;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.gwtorm.server.ListResultSet;
import com.google.gwtorm.server.OrmException;
import com.google.gwtorm.server.OrmRuntimeException;
import com.google.gwtorm.server.ResultSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class AndSource<T> extends AndPredicate<T> implements DataSource<T>, Comparator<Predicate<T>> {
    protected final DataSource<T> source;

    private final IsVisibleToPredicate<T> isVisibleToPredicate;
    private final int start;
    private final int cardinality;

    public AndSource(Collection<? extends Predicate<T>> that) {
        this(that, null, 0);
    }

    public AndSource(Predicate<T> that, IsVisibleToPredicate<T> isVisibleToPredicate) {
        this(that, isVisibleToPredicate, 0);
    }

    public AndSource(Predicate<T> that, IsVisibleToPredicate<T> isVisibleToPredicate, int start) {
        this(ImmutableList.of(that), isVisibleToPredicate, start);
    }

    public AndSource(Collection<? extends Predicate<T>> that, IsVisibleToPredicate<T> isVisibleToPredicate,
            int start) {
        super(that);
        checkArgument(start >= 0, "negative start: %s", start);
        this.isVisibleToPredicate = isVisibleToPredicate;
        this.start = start;

        int c = Integer.MAX_VALUE;
        DataSource<T> s = null;
        int minCost = Integer.MAX_VALUE;
        for (Predicate<T> p : sort(getChildren())) {
            if (p instanceof DataSource) {
                c = Math.min(c, ((DataSource<?>) p).getCardinality());

                int cost = p.estimateCost();
                if (cost < minCost) {
                    s = toDataSource(p);
                    minCost = cost;
                }
            }
        }
        this.source = s;
        this.cardinality = c;
    }

    @Override
    public ResultSet<T> read() throws OrmException {
        try {
            return readImpl();
        } catch (OrmRuntimeException err) {
            if (err.getCause() != null) {
                Throwables.throwIfInstanceOf(err.getCause(), OrmException.class);
            }
            throw new OrmException(err);
        }
    }

    private ResultSet<T> readImpl() throws OrmException {
        if (source == null) {
            throw new OrmException("No DataSource: " + this);
        }
        List<T> r = new ArrayList<>();
        T last = null;
        int nextStart = 0;
        boolean skipped = false;
        for (T data : buffer(source.read())) {
            if (!isMatchable() || match(data)) {
                r.add(data);
            } else {
                skipped = true;
            }
            last = data;
            nextStart++;
        }

        if (skipped && last != null && source instanceof Paginated) {
            // If our source is a paginated source and we skipped at
            // least one of its results, we may not have filled the full
            // limit the caller wants.  Restart the source and continue.
            //
            @SuppressWarnings("unchecked")
            Paginated<T> p = (Paginated<T>) source;
            while (skipped && r.size() < p.getOptions().limit() + start) {
                skipped = false;
                ResultSet<T> next = p.restart(nextStart);

                for (T data : buffer(next)) {
                    if (match(data)) {
                        r.add(data);
                    } else {
                        skipped = true;
                    }
                    nextStart++;
                }
            }
        }

        if (start >= r.size()) {
            r = ImmutableList.of();
        } else if (start > 0) {
            r = ImmutableList.copyOf(r.subList(start, r.size()));
        }
        return new ListResultSet<>(r);
    }

    @Override
    public boolean isMatchable() {
        return isVisibleToPredicate != null || super.isMatchable();
    }

    @Override
    public boolean match(T object) throws OrmException {
        if (isVisibleToPredicate != null && !isVisibleToPredicate.match(object)) {
            return false;
        }

        if (super.isMatchable() && !super.match(object)) {
            return false;
        }

        return true;
    }

    private Iterable<T> buffer(ResultSet<T> scanner) {
        return FluentIterable.from(Iterables.partition(scanner, 50)).transformAndConcat(this::transformBuffer);
    }

    protected List<T> transformBuffer(List<T> buffer) throws OrmRuntimeException {
        return buffer;
    }

    @Override
    public int getCardinality() {
        return cardinality;
    }

    private List<Predicate<T>> sort(Collection<? extends Predicate<T>> that) {
        List<Predicate<T>> r = new ArrayList<>(that);
        Collections.sort(r, this);
        return r;
    }

    @Override
    public int compare(Predicate<T> a, Predicate<T> b) {
        int ai = a instanceof DataSource ? 0 : 1;
        int bi = b instanceof DataSource ? 0 : 1;
        int cmp = ai - bi;

        if (cmp == 0) {
            cmp = a.estimateCost() - b.estimateCost();
        }

        if (cmp == 0 && a instanceof DataSource && b instanceof DataSource) {
            DataSource<?> as = (DataSource<?>) a;
            DataSource<?> bs = (DataSource<?>) b;
            cmp = as.getCardinality() - bs.getCardinality();
        }
        return cmp;
    }

    @SuppressWarnings("unchecked")
    private DataSource<T> toDataSource(Predicate<T> pred) {
        return (DataSource<T>) pred;
    }
}