1 /* 2 * Copyright 2016 Google Inc. All Rights Reserved. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.turbine.binder.env; 18 19 import com.google.common.base.Joiner; 20 import com.google.common.collect.ImmutableMap; 21 import com.google.turbine.binder.sym.Symbol; 22 import java.util.LinkedHashMap; 23 import java.util.LinkedHashSet; 24 import java.util.Map; 25 26 /** 27 * An env that permits an analysis pass to access information about symbols from the current pass, 28 * recursively. Cycles are detected, and result in an {@link LazyBindingError} being thrown. 29 * 30 * <p>This is used primarily for resolving the supertype hierarchy in {@link HierarchyBinder}. The 31 * supertype hierarchy forms a directed acyclic graph, and {@link HierarchyBinder} needs to process 32 * classes in a topological sort order of that graph. Unfortuntately, we can't produce a suitable 33 * sort order until the graph exists. 34 * 35 * @param <T> the interface type of the bound node {@link V}, shared by any underlying environments. 36 * @param <V> a specific implementation of {@code T}. For example, during hierarchy binding {@link 37 * SourceHeaderBoundClass} nodes are being completed from the sources being compiled, and the 38 * analysis of a given symbol may require looking up {@link HeaderBoundClass} nodes that will 39 * either be backed by other {@link SourceHeaderBoundClass} nodes or {@link BytecodeBoundClass} 40 * nodes. So the phase uses an {@link LazyEnv<HeaderBoundClass, SourceHeaderBoundClass>}. 41 */ 42 public class LazyEnv<S extends Symbol, T, V extends T> implements Env<S, V> { 43 44 /** The list of symbols that are currently being processed, used to check for cycles. */ 45 private final LinkedHashSet<S> seen = new LinkedHashSet<>(); 46 47 /** Lazy value providers for the symbols in the environment. */ 48 private final ImmutableMap<S, Completer<S, T, V>> completers; 49 50 /** Values that have already been computed. */ 51 private final Map<S, V> cache = new LinkedHashMap<>(); 52 53 /** An underlying env of already-computed {@code T}s that can be queried during completion. */ 54 private final Env<S, T> rec; 55 56 public LazyEnv(ImmutableMap<S, Completer<S, T, V>> completers, Env<S, ? extends T> base) { 57 this.completers = completers; 58 this.rec = CompoundEnv.<S, T>of(base).append(this); 59 } 60 61 @Override 62 public V get(S sym) { 63 V v = cache.get(sym); 64 if (v != null) { 65 return v; 66 } 67 Completer<S, T, V> completer = completers.get(sym); 68 if (completer != null) { 69 if (!seen.add(sym)) { 70 throw new LazyBindingError(Joiner.on(" -> ").join(seen) + " -> " + sym); 71 } 72 v = completer.complete(rec, sym); 73 seen.remove(sym); 74 cache.put(sym, v); 75 return v; 76 } 77 return null; 78 } 79 80 /** A lazy value provider which is given access to the current environment. */ 81 public interface Completer<S extends Symbol, T, V extends T> { 82 /** Provides the value for the given symbol in the current environment. */ 83 V complete(Env<S, T> env, S k); 84 } 85 86 /** Indicates that a completer tried to complete itself, possibly transitively. */ 87 public static class LazyBindingError extends Error { 88 public LazyBindingError(String message) { 89 super(message); 90 } 91 } 92 } 93
