Java tutorial
/* * Copyright (C) 2015 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.android.build.gradle.internal.incremental; import com.android.annotations.NonNull; import com.google.common.collect.Lists; import java.util.ArrayList; import java.util.Arrays; import java.util.HashSet; import java.util.LinkedHashSet; import java.util.List; import java.util.Set; import org.objectweb.asm.Opcodes; import org.objectweb.asm.Type; import org.objectweb.asm.commons.GeneratorAdapter; import org.objectweb.asm.tree.AbstractInsnNode; import org.objectweb.asm.tree.LabelNode; import org.objectweb.asm.tree.LineNumberNode; import org.objectweb.asm.tree.LocalVariableNode; import org.objectweb.asm.tree.MethodInsnNode; import org.objectweb.asm.tree.MethodNode; import org.objectweb.asm.tree.TryCatchBlockNode; import org.objectweb.asm.tree.VarInsnNode; import org.objectweb.asm.tree.analysis.Analyzer; import org.objectweb.asm.tree.analysis.AnalyzerException; import org.objectweb.asm.tree.analysis.BasicInterpreter; import org.objectweb.asm.tree.analysis.BasicValue; import org.objectweb.asm.tree.analysis.Frame; import org.objectweb.asm.tree.analysis.Value; /** * Builds a constructor object separating all its components. * * A generic constructor has the following form: * <pre>{@code * ... // Code to set up this (specially for inner classes). This code * ... // Is arbitrary with the exception of sending the "this" object * ... // as a method argument is not allowed. * ... // Note that local variables can be declared here. * ... // This is considered the "prelude" section, and cannot be hot swapped. * ALOAD_0 // This is the last ALOAD_0 before the "super" call. * ... // Code to set up the arguments (aka "args") for the delegation * ... // via super() or this(). Note that here we can have INVOKESPECIALS * ... // for all the new calls here. * ... // Again in this section, "this" cannot escape, and local variables can * ... // be created. * INVOKESPECIAL <init> // super() or this() call * ... // the "body" of the constructor goes here. * }</pre> * This class has the utilities to detect which instruction is the right INVOKESPECIAL call before * the "body". */ public class ConstructorBuilder { /** * A specialized value used to track the first local variable (this) on the * constructor. */ public static class LocalValue extends BasicValue { public LocalValue(Type type) { super(type); } @Override public String toString() { return "*"; } } /** * Deconstruct a constructor into its components and adds the necessary code to link the components * later. This code is not valid java, but it can be expressed in bytecode. In essence for this constructor: * <pre>{@code * <init>(int x) { * int a = 2; * super(int b = 3, x = 1, expr2() ? 3 : a++) * doSomething(x + a) * } * }</pre> * it creates two parts: * <pre>{@code * Object[] init$args(Clazz this, int x, Object[] locals) { // this is always null here * int a = locals[0]; * int b = 3; * Object[] args = new Object[3]; * args[0] = b; * args[1] = (x = 1) * args[2] = expr2() ? 3 : a++; * locals = new Object[3]; // The arguments + the locals * locals[0] = NULL; * locals[1] = x; * locals[2] = new Object[2]; * locals[2][0] = a; * locals[2][1] = b; * return new Object[] {locals, "myclass.<init>(I;I;)V", args}; * } * * void init$body(int x, Object[] locals) { * int a = locals[0]; * int b = locals[1]; * doSomething(x + a); * } * }</pre> * * @param owner the owning class. * @param method the constructor method. */ @NonNull public static Constructor build(@NonNull String owner, @NonNull MethodNode method) { // Basic interpreter uses BasicValue.REFERENCE_VALUE for all object types. However // we need to distinguish one in particular. The value of the local variable 0, ie. the // uninitialized this. By doing it this way we ensure that whenever there is a ALOAD_0 // a LocalValue instance will be on the stack. BasicInterpreter interpreter = new BasicInterpreter() { boolean done = false; @Override // newValue is called first to initialize the frame values of all the local variables // we intercept the first one to create our own special value. public BasicValue newValue(Type type) { if (type == null) { return BasicValue.UNINITIALIZED_VALUE; } else if (type.getSort() == Type.VOID) { return null; } else { // If this is the first value created (i.e. the first local variable) // we use a special marker. BasicValue ret = done ? super.newValue(type) : new LocalValue(type); done = true; return ret; } } }; Analyzer analyzer = new Analyzer(interpreter); AbstractInsnNode[] instructions = method.instructions.toArray(); try { Frame[] frames = analyzer.analyze(owner, method); if (frames.length != instructions.length) { // Should never happen. throw new IllegalStateException("The number of frames is not equals to the number of instructions"); } int stackAtThis = -1; boolean poppedThis = false; int firstLocal = 1; for (Type type : Type.getArgumentTypes(method.desc)) { firstLocal += type.getSize(); } LinkedHashSet<LocalVariable> variables = new LinkedHashSet<LocalVariable>(); VarInsnNode lastThis = null; int localsAtLastThis = 0; // Records the most recent line number encountered. For javac, there should always be // a line number node before the call of interest to this(...) or super(...). For robustness, // -1 is recorded as a sentinel to indicate this assumption didn't hold. Upstream consumers // should check for -1 and recover in a reasonable way (for example, don't set the line // number in generated code). int recentLine = -1; for (int i = 0; i < instructions.length; i++) { AbstractInsnNode insn = instructions[i]; Frame frame = frames[i]; if (frame.getStackSize() < stackAtThis) { poppedThis = true; } if (insn instanceof MethodInsnNode) { // TODO: Do we need to check that the stack is empty after this super call? MethodInsnNode methodhInsn = (MethodInsnNode) insn; Type[] types = Type.getArgumentTypes(methodhInsn.desc); Value value = frame.getStack(frame.getStackSize() - types.length - 1); if (value instanceof LocalValue && methodhInsn.name.equals("<init>")) { if (poppedThis) { throw new IllegalStateException("Unexpected constructor structure."); } return split(owner, method, lastThis, methodhInsn, recentLine, new ArrayList<LocalVariable>(variables), localsAtLastThis); } } else if (insn instanceof VarInsnNode) { VarInsnNode var = (VarInsnNode) insn; if (var.var == 0) { lastThis = var; localsAtLastThis = variables.size(); stackAtThis = frame.getStackSize(); poppedThis = false; } Type type = ByteCodeUtils.getTypeForStoreOpcode(var.getOpcode()); if (type != null && var.var >= firstLocal) { // Variables are equals based on their number, so they will be added // to the set only if they are new, and in the order they are seen. variables.add(new LocalVariable(type, var.var)); } } else if (insn instanceof LineNumberNode) { // Record the most recent line number encountered so that call to this(...) // or super(...) has line number information. Ultimately used to emit a line // number in the generated code. LineNumberNode lineNumberNode = (LineNumberNode) insn; recentLine = lineNumberNode.line; } } throw new IllegalStateException("Unexpected constructor structure."); } catch (AnalyzerException e) { throw new IllegalStateException(e); } } /** * Splits the constructor in two methods, the "set up" and the "body" parts (see above). */ @NonNull private static Constructor split(@NonNull String owner, @NonNull MethodNode method, @NonNull VarInsnNode loadThis, @NonNull MethodInsnNode delegation, int loadThisLine, @NonNull List<LocalVariable> variables, int localsAtLoadThis) { String[] exceptions = ((List<String>) method.exceptions).toArray(new String[method.exceptions.size()]); // Do not add the local array yet, as we treat it as a new variable. String newDesc = method.desc.replace(")V", ")Ljava/lang/Object;"); newDesc = newDesc.replace("(", "([L" + owner + ";"); Type[] argumentTypes = Type.getArgumentTypes(newDesc); // Store the non hotswappable part of the constructor List<AbstractInsnNode> fixed = Lists.newLinkedList(); AbstractInsnNode insn = method.instructions.getFirst(); while (insn != loadThis) { fixed.add(insn); insn = insn.getNext(); } fixed.add(loadThis); MethodNode initArgs = new MethodNode(Opcodes.ACC_PUBLIC | Opcodes.ACC_STATIC, "init$args", newDesc, null, exceptions); GeneratorAdapter mv = new GeneratorAdapter(initArgs, initArgs.access, initArgs.name, initArgs.desc); int newArgument = mv.newLocal(Type.getType("[Ljava/lang/Object;")); mv.loadLocal(newArgument); ByteCodeUtils.restoreVariables(mv, variables.subList(0, localsAtLoadThis)); // Now insert the original method insn = loadThis.getNext(); while (insn != delegation) { insn.accept(mv); insn = insn.getNext(); } LabelNode labelBefore = new LabelNode(); labelBefore.accept(mv); // Create the args array with the local variables and the values to send to the delegated constructor Type[] returnTypes = Type.getArgumentTypes(delegation.desc); // The extra elements for the local variables and the qualified name of the constructor. mv.push(returnTypes.length + 2); mv.newArray(Type.getType(Object.class)); int args = mv.newLocal(Type.getType("[Ljava/lang/Object;")); mv.storeLocal(args); for (int i = returnTypes.length - 1; i >= 0; i--) { Type type = returnTypes[i]; mv.loadLocal(args); mv.swap(type, Type.getType(Object.class)); mv.push(i + 2); mv.swap(type, Type.INT_TYPE); mv.box(type); mv.arrayStore(Type.getType(Object.class)); } // Store the qualified name of the constructor in the second element of the array. mv.loadLocal(args); mv.push(1); mv.push(delegation.owner + "." + delegation.desc); // Name of the constructor to be called. mv.arrayStore(Type.getType(Object.class)); // Create the locals array and place it in the first element of the return array mv.loadLocal(args); mv.push(0); mv.push(argumentTypes.length + 1); mv.newArray(Type.getType(Object.class)); ByteCodeUtils.loadVariableArray(mv, ByteCodeUtils.toLocalVariables(Arrays.asList(argumentTypes)), 0); mv.dup(); mv.push(argumentTypes.length); ByteCodeUtils.newVariableArray(mv, variables); mv.arrayStore(Type.getType(Object.class)); mv.arrayStore(Type.getType(Object.class)); mv.loadLocal(args); mv.returnValue(); // Move the first variable up to be an argument initArgs.desc = initArgs.desc.replace(")", "[Ljava/lang/Object;)"); newDesc = method.desc.replace("(", "(L" + owner + ";"); MethodNode body = new MethodNode(Opcodes.ACC_PUBLIC | Opcodes.ACC_STATIC, "init$body", newDesc, null, exceptions); mv = new GeneratorAdapter(body, body.access, body.name, body.desc); newArgument = mv.newLocal(Type.getType("[Ljava/lang/Object;")); LabelNode labelAfter = new LabelNode(); labelAfter.accept(body); Set<LabelNode> bodyLabels = new HashSet<LabelNode>(); mv.loadLocal(newArgument); ByteCodeUtils.restoreVariables(mv, variables); insn = delegation.getNext(); while (insn != null) { if (insn instanceof LabelNode) { bodyLabels.add((LabelNode) insn); } insn.accept(mv); insn = insn.getNext(); } // manually transfer the exception table from the existing constructor to the new // "init$body" method. The labels were transferred just above so we can reuse them. //noinspection unchecked for (TryCatchBlockNode tryCatch : (List<TryCatchBlockNode>) method.tryCatchBlocks) { tryCatch.accept(mv); } //noinspection unchecked for (LocalVariableNode variable : (List<LocalVariableNode>) method.localVariables) { boolean startsInBody = bodyLabels.contains(variable.start); boolean endsInBody = bodyLabels.contains(variable.end); if (!startsInBody && !endsInBody) { if (variable.index != 0) { // '#0' on init$args is not 'this' variable.accept(initArgs); } } else if (startsInBody && endsInBody) { variable.accept(body); } else if (!startsInBody && endsInBody) { // The variable spans from the args to the end of the method, create two: if (variable.index != 0) { // '#0' on init$args is not 'this' LocalVariableNode var0 = new LocalVariableNode(variable.name, variable.desc, variable.signature, variable.start, labelBefore, variable.index); var0.accept(initArgs); } LocalVariableNode var1 = new LocalVariableNode(variable.name, variable.desc, variable.signature, labelAfter, variable.end, variable.index); var1.accept(body); } else { throw new IllegalStateException("Local variable starts after it ends."); } } // Move the first variable up to be an argument body.desc = body.desc.replace(")", "[Ljava/lang/Object;)"); return new Constructor(owner, fixed, loadThis, loadThisLine, initArgs, delegation, body, variables, localsAtLoadThis); } }