// Copyright (C) 2011 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.rules;
import static com.googlecode.prolog_cafe.lang.PrologMachineCopy.save;
import com.google.gerrit.reviewdb.client.Project;
import com.google.gerrit.server.config.GerritServerConfig;
import com.google.gerrit.server.config.SitePaths;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.inject.Inject;
import com.google.inject.Singleton;
import com.googlecode.prolog_cafe.compiler.CompileException;
import com.googlecode.prolog_cafe.lang.BufferingPrologControl;
import com.googlecode.prolog_cafe.lang.JavaObjectTerm;
import com.googlecode.prolog_cafe.lang.Prolog;
import com.googlecode.prolog_cafe.lang.PrologClassLoader;
import com.googlecode.prolog_cafe.lang.PrologMachineCopy;
import com.googlecode.prolog_cafe.lang.SymbolTerm;
import org.eclipse.jgit.errors.LargeObjectException;
import org.eclipse.jgit.errors.RepositoryNotFoundException;
import org.eclipse.jgit.lib.Config;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectLoader;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.util.RawParseUtils;
import java.io.File;
import java.io.IOException;
import java.io.PushbackReader;
import java.io.StringReader;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.Map;
/**
* Manages a cache of compiled Prolog rules.
* <p>
* Rules are loaded from the {@code site_path/cache/rules/rules-SHA1.jar}, where
* {@code SHA1} is the SHA1 of the Prolog {@code rules.pl} in a project's
* {@link GitRepositoryManager#REF_CONFIG} branch.
*/
@Singleton
public class RulesCache {
/** Maximum size of a dynamic Prolog script, in bytes. */
private static final int SRC_LIMIT = 128 * 1024;
/** Default size of the internal Prolog database within each interpreter. */
private static final int DB_MAX = 256;
private static final String[] PACKAGE_LIST = {
Prolog.BUILTIN,
"gerrit",
};
private final Map<ObjectId, MachineRef> machineCache =
new HashMap<ObjectId, MachineRef>();
private final ReferenceQueue<PrologMachineCopy> dead =
new ReferenceQueue<PrologMachineCopy>();
private static final class MachineRef extends WeakReference<PrologMachineCopy> {
final ObjectId key;
MachineRef(ObjectId key, PrologMachineCopy pcm,
ReferenceQueue<PrologMachineCopy> queue) {
super(pcm, queue);
this.key = key;
}
}
private final boolean enableProjectRules;
private final File cacheDir;
private final File rulesDir;
private final GitRepositoryManager gitMgr;
private final ClassLoader systemLoader;
private final PrologMachineCopy defaultMachine;
@Inject
protected RulesCache(@GerritServerConfig Config config, SitePaths site,
GitRepositoryManager gm) {
enableProjectRules = config.getBoolean("rules", null, "enable", true);
cacheDir = site.resolve(config.getString("cache", null, "directory"));
rulesDir = cacheDir != null ? new File(cacheDir, "rules") : null;
gitMgr = gm;
systemLoader = getClass().getClassLoader();
defaultMachine = save(newEmptyMachine(systemLoader));
}
/**
* Locate a cached Prolog machine state, or create one if not available.
*
* @return a Prolog machine, after loading the specified rules.
* @throws CompileException the machine cannot be created.
*/
public synchronized PrologMachineCopy loadMachine(
Project.NameKey project,
ObjectId rulesId)
throws CompileException {
if (!enableProjectRules || project == null || rulesId == null) {
return defaultMachine;
}
Reference<? extends PrologMachineCopy> ref = machineCache.get(rulesId);
if (ref != null) {
PrologMachineCopy pmc = ref.get();
if (pmc != null) {
return pmc;
}
machineCache.remove(rulesId);
ref.enqueue();
}
gc();
PrologMachineCopy pcm = createMachine(project, rulesId);
MachineRef newRef = new MachineRef(rulesId, pcm, dead);
machineCache.put(rulesId, newRef);
return pcm;
}
private void gc() {
Reference<?> ref;
while ((ref = dead.poll()) != null) {
ObjectId key = ((MachineRef) ref).key;
if (machineCache.get(key) == ref) {
machineCache.remove(key);
}
}
}
private PrologMachineCopy createMachine(Project.NameKey project,
ObjectId rulesId) throws CompileException {
// If the rules are available as a complied JAR on local disk, prefer
// that over dynamic consult as the bytecode will be faster.
//
if (rulesDir != null) {
File jarFile = new File(rulesDir, "rules-" + rulesId.getName() + ".jar");
if (jarFile.isFile()) {
URL[] cp = new URL[] {toURL(jarFile)};
return save(newEmptyMachine(new URLClassLoader(cp, systemLoader)));
}
}
// Dynamically consult the rules into the machine's internal database.
//
String rules = read(project, rulesId);
BufferingPrologControl ctl = newEmptyMachine(systemLoader);
PushbackReader in = new PushbackReader(
new StringReader(rules),
Prolog.PUSHBACK_SIZE);
if (!ctl.execute(
Prolog.BUILTIN, "consult_stream",
SymbolTerm.intern("rules.pl"),
new JavaObjectTerm(in))) {
throw new CompileException("Cannot consult rules of " + project);
}
return save(ctl);
}
private String read(Project.NameKey project, ObjectId rulesId)
throws CompileException {
Repository git;
try {
git = gitMgr.openRepository(project);
} catch (RepositoryNotFoundException e) {
throw new CompileException("Cannot open repository " + project, e);
} catch (IOException e) {
throw new CompileException("Cannot open repository " + project, e);
}
try {
ObjectLoader ldr = git.open(rulesId, Constants.OBJ_BLOB);
byte[] raw = ldr.getCachedBytes(SRC_LIMIT);
return RawParseUtils.decode(raw);
} catch (LargeObjectException e) {
throw new CompileException("rules of " + project + " are too large", e);
} catch (RuntimeException e) {
throw new CompileException("Cannot load rules of " + project, e);
} catch (IOException e) {
throw new CompileException("Cannot load rules of " + project, e);
} finally {
git.close();
}
}
private static BufferingPrologControl newEmptyMachine(ClassLoader cl) {
BufferingPrologControl ctl = new BufferingPrologControl();
ctl.setMaxArity(PrologEnvironment.MAX_ARITY);
ctl.setMaxDatabaseSize(DB_MAX);
ctl.setPrologClassLoader(new PrologClassLoader(cl));
ctl.setEnabled(EnumSet.allOf(Prolog.Feature.class), false);
// Bootstrap the interpreter and ensure there is clean state.
ctl.initialize(PACKAGE_LIST);
return ctl;
}
private static URL toURL(File jarFile) throws CompileException {
try {
return jarFile.toURI().toURL();
} catch (MalformedURLException e) {
throw new CompileException("Cannot create URL for " + jarFile, e);
}
}
}