https://openjdk.java.net/ 
/*
 * Copyright (c) 2015, 2020, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.tools.javac.api;

import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.Writer;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;

import javax.tools.Diagnostic;
import javax.tools.DiagnosticListener;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;

import com.sun.source.tree.ClassTree;
import com.sun.source.tree.CompilationUnitTree;
import com.sun.source.tree.Tree;
import com.sun.source.util.JavacTask;
import com.sun.source.util.TaskEvent;
import com.sun.source.util.TaskEvent.Kind;
import com.sun.source.util.TaskListener;
import com.sun.source.util.TreeScanner;
import com.sun.tools.javac.code.Kinds;
import com.sun.tools.javac.code.Preview;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symtab;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.code.Type.ClassType;
import com.sun.tools.javac.code.TypeTag;
import com.sun.tools.javac.code.Types;
import com.sun.tools.javac.comp.Annotate;
import com.sun.tools.javac.comp.Check;
import com.sun.tools.javac.comp.CompileStates;
import com.sun.tools.javac.comp.Enter;
import com.sun.tools.javac.comp.Modules;
import com.sun.tools.javac.main.Arguments;
import com.sun.tools.javac.main.JavaCompiler;
import com.sun.tools.javac.model.JavacElements;
import com.sun.tools.javac.platform.PlatformDescription;
import com.sun.tools.javac.tree.JCTree.JCClassDecl;
import com.sun.tools.javac.tree.JCTree.LetExpr;
import com.sun.tools.javac.util.Context;
import com.sun.tools.javac.util.DefinedBy;
import com.sun.tools.javac.util.DefinedBy.Api;
import com.sun.tools.javac.util.Log;
import com.sun.tools.javac.util.Options;


A pool of reusable JavacTasks. When a task is no valid anymore, it is returned to the pool,
and its Context may be reused for future processing in some cases. The reuse is achieved
by replacing some components (most notably JavaCompiler and Log) with reusable counterparts,
and by cleaning up leftovers from previous compilation.


For each combination of options, a separate task/context is created and kept, as most option
values are cached inside components themselves.


When the compilation redefines sensitive classes (e.g. classes in the the java.* packages), the
task/context is not reused.


When the task is reused, then packages that were already listed won't be listed again.


Care must be taken to only return tasks that won't be used by the original caller.


Care must also be taken when custom components are installed, as those are not cleaned when the
task/context is reused, and subsequent getTask may return a task based on a context with these
custom components.

This is NOT part of any supported API.
If you write code that depends on this, you do so at your own risk.
This code and its internal interfaces are subject to change or
deletion without notice.

/**
 * A pool of reusable JavacTasks. When a task is no valid anymore, it is returned to the pool,
 * and its Context may be reused for future processing in some cases. The reuse is achieved
 * by replacing some components (most notably JavaCompiler and Log) with reusable counterparts,
 * and by cleaning up leftovers from previous compilation.
 * <p>
 * For each combination of options, a separate task/context is created and kept, as most option
 * values are cached inside components themselves.
 * <p>
 * When the compilation redefines sensitive classes (e.g. classes in the the java.* packages), the
 * task/context is not reused.
 * <p>
 * When the task is reused, then packages that were already listed won't be listed again.
 * <p>
 * Care must be taken to only return tasks that won't be used by the original caller.
 * <p>
 * Care must also be taken when custom components are installed, as those are not cleaned when the
 * task/context is reused, and subsequent getTask may return a task based on a context with these
 * custom components.
 *
 * <p><b>This is NOT part of any supported API.
 * If you write code that depends on this, you do so at your own risk.
 * This code and its internal interfaces are subject to change or
 * deletion without notice.</b>
 */
public class JavacTaskPool {

    private static final JavacTool systemProvider = JavacTool.create();
    private static final Queue<ReusableContext> EMPTY_QUEUE = new ArrayDeque<>(0);

    private final int maxPoolSize;
    private final Map<List<String>, Queue<ReusableContext>> options2Contexts = new HashMap<>();
    private int id;

    private int statReused = 0;
    private int statNew = 0;
    private int statPolluted = 0;
    private int statRemoved = 0;

    
Creates the pool.

Params:
  • maxPoolSize – maximum number of tasks/context that will be kept in the pool.
/**Creates the pool.
     *
     * @param maxPoolSize maximum number of tasks/context that will be kept in the pool.
     */
    public JavacTaskPool(int maxPoolSize) {
        this.maxPoolSize = maxPoolSize;
    }

    
Creates a new task as if by JavaCompiler.getTask and runs the provided worker with it. The task is only valid while the worker is running. The internal structures may be reused from some previous compilation. 
Params:
  • out – a Writer for additional output from the compiler; use System.err if null
  • fileManager – a file manager; if null use the compiler's standard file manager
  • diagnosticListener – a diagnostic listener; if 
null use the compiler's default method for reporting diagnostics
  • options – compiler options, null means no options
  • classes – names of classes to be processed by annotation processing, null means no class names
  • compilationUnits – the compilation units to compile, 
null means no compilation units
  • worker – that should be run with the task
Throws:
  • RuntimeException – if an unrecoverable error occurred in a user supplied component. The cause will be the error in user code.
  • IllegalArgumentException – if any of the options are invalid, or if any of the given compilation units are of other kind than source
Returns:an object representing the compilation
/**Creates a new task as if by {@link javax.tools.JavaCompiler#getTask} and runs the provided
     * worker with it. The task is only valid while the worker is running. The internal structures
     * may be reused from some previous compilation.
     *
     * @param out a Writer for additional output from the compiler;
     * use {@code System.err} if {@code null}
     * @param fileManager a file manager; if {@code null} use the
     * compiler's standard file manager
     * @param diagnosticListener a diagnostic listener; if {@code
     * null} use the compiler's default method for reporting
     * diagnostics
     * @param options compiler options, {@code null} means no options
     * @param classes names of classes to be processed by annotation
     * processing, {@code null} means no class names
     * @param compilationUnits the compilation units to compile, {@code
     * null} means no compilation units
     * @param worker that should be run with the task
     * @return an object representing the compilation
     * @throws RuntimeException if an unrecoverable error
     * occurred in a user supplied component.  The
     * {@linkplain Throwable#getCause() cause} will be the error in
     * user code.
     * @throws IllegalArgumentException if any of the options are invalid,
     * or if any of the given compilation units are of other kind than
     * {@linkplain JavaFileObject.Kind#SOURCE source}
     */
    public <Z> Z getTask(Writer out,
                         JavaFileManager fileManager,
                         DiagnosticListener<? super JavaFileObject> diagnosticListener,
                         Iterable<String> options,
                         Iterable<String> classes,
                         Iterable<? extends JavaFileObject> compilationUnits,
                         Worker<Z> worker) {
        List<String> opts =
                StreamSupport.stream(options.spliterator(), false)
                             .collect(Collectors.toCollection(ArrayList::new));

        ReusableContext ctx;

        synchronized (this) {
            Queue<ReusableContext> cached =
                    options2Contexts.getOrDefault(opts, EMPTY_QUEUE);

            if (cached.isEmpty()) {
                ctx = new ReusableContext(opts);
                statNew++;
            } else {
                ctx = cached.remove();
                statReused++;
            }
        }

        ctx.useCount++;

        JavacTaskImpl task =
                (JavacTaskImpl) systemProvider.getTask(out, fileManager, diagnosticListener,
                                                       opts, classes, compilationUnits, ctx);

        task.addTaskListener(ctx);

        if (out != null) {
            Log.instance(ctx).setWriters(new PrintWriter(out, true));
        }

        Z result = worker.withTask(task);

        //not returning the context to the pool if task crashes with an exception
        //the task/context may be in a broken state
        ctx.clear();
        if (ctx.polluted) {
            statPolluted++;
        } else {
            task.cleanup();
            synchronized (this) {
                while (cacheSize() + 1 > maxPoolSize) {
                    ReusableContext toRemove =
                            options2Contexts.values()
                                            .stream()
                                            .flatMap(Collection::stream)
                                            .sorted((c1, c2) -> c1.timeStamp < c2.timeStamp ? -1 : 1)
                                            .findFirst()
                                            .get();
                    options2Contexts.get(toRemove.arguments).remove(toRemove);
                    statRemoved++;
                }
                options2Contexts.computeIfAbsent(ctx.arguments, x -> new ArrayDeque<>()).add(ctx);
                ctx.timeStamp = id++;
            }
        }

        return result;
    }
    //where:
        private long cacheSize() {
            return options2Contexts.values().stream().flatMap(Collection::stream).count();
        }

    public void printStatistics(PrintStream out) {
        out.println(statReused + " reused Contexts");
        out.println(statNew + " newly created Contexts");
        out.println(statPolluted + " polluted Contexts");
        out.println(statRemoved + " removed Contexts");
    }

    public interface Worker<Z> {
        public Z withTask(JavacTask task);
    }

    static class ReusableContext extends Context implements TaskListener {

        Set<CompilationUnitTree> roots = new HashSet<>();

        List<String> arguments;
        boolean polluted = false;

        int useCount;
        long timeStamp;

        ReusableContext(List<String> arguments) {
            super();
            this.arguments = arguments;
            put(Log.logKey, ReusableLog.factory);
            put(JavaCompiler.compilerKey, ReusableJavaCompiler.factory);
        }

        void clear() {
            drop(Arguments.argsKey);
            drop(DiagnosticListener.class);
            drop(Log.outKey);
            drop(Log.errKey);
            drop(JavaFileManager.class);
            drop(JavacTask.class);
            drop(JavacTrees.class);
            drop(JavacElements.class);
            drop(PlatformDescription.class);

            if (ht.get(Log.logKey) instanceof ReusableLog) {
                //log already inited - not first round
                ((ReusableLog)Log.instance(this)).clear();
                Enter.instance(this).newRound();
                ((ReusableJavaCompiler)ReusableJavaCompiler.instance(this)).clear();
                Types.instance(this).newRound();
                Check.instance(this).newRound();
                Check.instance(this).clear(); //clear mandatory warning handlers
                Preview.instance(this).clear(); //clear mandatory warning handlers
                Modules.instance(this).newRound();
                Annotate.instance(this).newRound();
                CompileStates.instance(this).clear();
                MultiTaskListener.instance(this).clear();
                Options.instance(this).clear();

                //find if any of the roots have redefined java.* classes
                Symtab syms = Symtab.instance(this);
                pollutionScanner.scan(roots, syms);
                roots.clear();
            }
        }

        
This scanner detects as to whether the shared context has been polluted. This happens
whenever a compiled program redefines a core class (in 'java.*' package) or when
(typically because of cyclic inheritance) the symbol kind of a core class has been touched.

/**
         * This scanner detects as to whether the shared context has been polluted. This happens
         * whenever a compiled program redefines a core class (in 'java.*' package) or when
         * (typically because of cyclic inheritance) the symbol kind of a core class has been touched.
         */
        TreeScanner<Void, Symtab> pollutionScanner = new TreeScanner<Void, Symtab>() {
            @Override @DefinedBy(Api.COMPILER_TREE)
            public Void scan(Tree tree, Symtab syms) {
                if (tree instanceof LetExpr) {
                    LetExpr le = (LetExpr) tree;
                    scan(le.defs, syms);
                    scan(le.expr, syms);
                    return null;
                } else {
                    return super.scan(tree, syms);
                }
            }

            @Override @DefinedBy(Api.COMPILER_TREE)
            public Void visitClass(ClassTree node, Symtab syms) {
                Symbol sym = ((JCClassDecl)node).sym;
                if (sym != null) {
                    syms.removeClass(sym.packge().modle, sym.flatName());
                    Type sup = supertype(sym);
                    if (isCoreClass(sym) ||
                            (sup != null && isCoreClass(sup.tsym) && sup.tsym.kind != Kinds.Kind.TYP)) {
                        polluted = true;
                    }
                }
                return super.visitClass(node, syms);
            }

            private boolean isCoreClass(Symbol s) {
                return s.flatName().toString().startsWith("java.");
            }

            private Type supertype(Symbol s) {
                if (s.type == null ||
                        !s.type.hasTag(TypeTag.CLASS)) {
                    return null;
                } else {
                    ClassType ct = (ClassType)s.type;
                    return ct.supertype_field;
                }
            }
        };

        @Override @DefinedBy(Api.COMPILER_TREE)
        public void finished(TaskEvent e) {
            if (e.getKind() == Kind.PARSE) {
                roots.add(e.getCompilationUnit());
            }
        }

        @Override @DefinedBy(Api.COMPILER_TREE)
        public void started(TaskEvent e) {
            //do nothing
        }

        <T> void drop(Key<T> k) {
            ht.remove(k);
        }

        <T> void drop(Class<T> c) {
            ht.remove(key(c));
        }

        
Reusable JavaCompiler; exposes a method to clean up the component from leftovers associated with
previous compilations.

/**
         * Reusable JavaCompiler; exposes a method to clean up the component from leftovers associated with
         * previous compilations.
         */
        static class ReusableJavaCompiler extends JavaCompiler {

            final static Factory<JavaCompiler> factory = ReusableJavaCompiler::new;

            ReusableJavaCompiler(Context context) {
                super(context);
            }

            @Override
            public void close() {
                //do nothing
            }

            void clear() {
                newRound();
            }

            @Override
            protected void checkReusable() {
                //do nothing - it's ok to reuse the compiler
            }
        }

        
Reusable Log; exposes a method to clean up the component from leftovers associated with
previous compilations.

/**
         * Reusable Log; exposes a method to clean up the component from leftovers associated with
         * previous compilations.
         */
        static class ReusableLog extends Log {

            final static Factory<Log> factory = ReusableLog::new;

            Context context;

            ReusableLog(Context context) {
                super(context);
                this.context = context;
            }

            void clear() {
                recorded.clear();
                sourceMap.clear();
                nerrors = 0;
                nwarnings = 0;
                //Set a fake listener that will lazily lookup the context for the 'real' listener. Since
                //this field is never updated when a new task is created, we cannot simply reset the field
                //or keep old value. This is a hack to workaround the limitations in the current infrastructure.
                diagListener = new DiagnosticListener<JavaFileObject>() {
                    DiagnosticListener<JavaFileObject> cachedListener;

                    @Override  @DefinedBy(Api.COMPILER)
                    @SuppressWarnings("unchecked")
                    public void report(Diagnostic<? extends JavaFileObject> diagnostic) {
                        if (cachedListener == null) {
                            cachedListener = context.get(DiagnosticListener.class);
                        }
                        cachedListener.report(diagnostic);
                    }
                };
            }
        }
    }
}