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ExportTable.java
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ExportTable.java
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/*
* The MIT License
*
* Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package hudson.remoting;
import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import javax.annotation.Nonnull;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.Date;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.ArrayList;
import java.util.concurrent.ExecutionException;
import java.util.logging.Level;
import java.util.logging.Logger;
import static java.util.logging.Level.*;
import javax.annotation.CheckForNull;
import javax.annotation.CheckReturnValue;
import javax.annotation.meta.When;
import org.kohsuke.accmod.Restricted;
import org.kohsuke.accmod.restrictions.NoExternalUse;
/**
* Manages unique ID for exported objects, and allows look-up from IDs.
*
* @author Kohsuke Kawaguchi
*/
final class ExportTable {
private final Map<Integer,Entry<?>> table = new HashMap<Integer,Entry<?>>();
private final Map<Object,Entry<?>> reverse = new HashMap<Object,Entry<?>>();
/**
* {@link ExportList}s which are actively recording the current
* export operation.
*/
private final ThreadLocal<ExportList> lists = new ThreadLocal<ExportList>();
/**
* For diagnosing problems like JENKINS-20707 where we seem to be unexporting too eagerly,
* record most recent unexported objects up to {@link #UNEXPORT_LOG_SIZE}
*
* New entries are added to the end, and older ones are removed from the beginning.
*/
private final List<Entry<?>> unexportLog = new LinkedList<Entry<?>>();
/**
* Information about one exported object.
*/
private final class Entry<T> {
final int id;
private Class<? super T>[] interfaces;
private T object;
/**
* {@code object.getClass().getName()} kept around so that we can see the type even after it
* gets deallocated.
*/
@Nonnull
private final String objectType;
/**
* Where was this object first exported?
*/
@Nonnull
final CreatedAt allocationTrace;
/**
* Where was this object unexported?
*/
@CheckForNull
ReleasedAt releaseTrace;
/**
* Current reference count.
* Access to {@link ExportTable} is guarded by synchronized block,
* so accessing this field requires no further synchronization.
*/
private int referenceCount;
/**
* This field can be set programmatically to track reference counting
*/
@CheckForNull
private ReferenceCountRecorder recorder;
Entry(@Nonnull T object, Class<? super T>... interfaces) {
this.id = iota++;
this.interfaces = interfaces.clone();
this.object = object;
this.objectType = object.getClass().getName();
this.allocationTrace = new CreatedAt();
table.put(id,this);
reverse.put(object,this);
}
void addRef() {
referenceCount++;
if (recorder!=null)
recorder.onAddRef(null);
}
/**
* Increase reference count so much to effectively prevent de-allocation.
* If the reference counting is correct, we just need to increment by one,
* but this makes it safer even in case of some reference counting errors
* (and we can still detect the problem by comparing the reference count with the magic value.
*/
void pin() {
// only add the magic constant if we are in the range Integer.MIN_VALUE < x < 0x2000000
// this means that over-reference removal will still yield a referece above 0 and repeated pinning
// will not yield a negative reference count.
// e.g. if we had:
// init -> 0x00000000;
// pin -> 0x40000001;
// release -> 0x39999999;
// pin -> 0x79999999;
// addRef -> 0x80000000 => BOOM
// By making the decision point half way, we give the maximum number of releases away from the pinned
// magic value
if (referenceCount<0x20000000)
referenceCount += 0x40000000;
}
/**
* Releases the entry.
* @param callSite
* Optional location that indicates where the actual call site was that triggered the activity,
* in case it was requested from the other side of the channel.
*/
void release(@CheckForNull Throwable callSite) {
if (recorder!=null)
recorder.onRelease(callSite);
if(--referenceCount==0) {
table.remove(id);
reverse.remove(object);
object = null;
releaseTrace = new ReleasedAt(callSite);
unexportLog.add(this);
while (unexportLog.size()>UNEXPORT_LOG_SIZE)
unexportLog.remove(0);
}
}
private String interfaceNames() {
StringBuilder buf = new StringBuilder(10 + getInterfaces().length * 128);
String sep = "[";
for (Class<? super T> clazz: getInterfaces()) {
buf.append(sep).append(clazz.getName());
sep = ", ";
}
buf.append("]");
return buf.toString();
}
/**
* Dumps the contents of the entry.
*/
void dump(PrintWriter w) throws IOException {
w.printf("#%d (ref.%d) : object=%s type=%s interfaces=%s%n", id, referenceCount, object, objectType, interfaceNames());
allocationTrace.printStackTrace(w);
if (releaseTrace!=null) {
releaseTrace.printStackTrace(w);
}
if (recorder!=null) {
recorder.dump(w);
}
}
String dump() {
try {
StringWriter sw = new StringWriter();
PrintWriter pw = new PrintWriter(sw);
dump(pw);
pw.close();
return sw.toString();
} catch (IOException e) {
throw new Error(e); // impossible
}
}
synchronized Class<? super T>[] getInterfaces() {
return interfaces;
}
synchronized void setInterfaces(Class<? super T>[] interfaces) {
this.interfaces = interfaces;
}
synchronized void addInterface(Class<? super T> clazz) {
for (Class<? super T> c: interfaces) {
if (c.equals(clazz)) return;
}
Class<? super T>[] replacement = new Class[interfaces.length+1];
System.arraycopy(interfaces, 0, replacement, 0, interfaces.length);
replacement[interfaces.length] = clazz;
interfaces = replacement;
}
}
static class Source extends Exception {
protected final long timestamp = System.currentTimeMillis();
/**
* @param callSite
* Optional location that indicates where the actual call site was that triggered the activity,
* in case it was requested from the other side of the channel.
*/
@SuppressWarnings("ResultOfMethodCallIgnored")
Source(@CheckForNull Throwable callSite) {
super(callSite);
updateOurStackTraceCache();
}
// TODO: We export the objects frequently, The current approach ALWAYS leads
// to creation of two Stacktrace arrays in the memory: the original and the cloned one
// Throwable API. Throwable API allows to workaround it only by using a heavy printStackTrace() method.
// Approach #1: Maybe a manual implementation of getOurStackTrace() and local storage is preferable.
// Approach #2: Consider disabling this logic by default
/**
* Update the internal stacktrace cache.
* Forces the computation of the stack trace in a Java friendly data structure,
* so that the call stack can be seen from the heap dump after the fact.
* @return Cloned version of the inner cache.
*/
@CheckReturnValue(when = When.NEVER)
protected final StackTraceElement[] updateOurStackTraceCache() {
return getStackTrace();
}
}
static class CreatedAt extends Source {
CreatedAt() {
super(null);
}
@Override
public String toString() {
return " Created at "+new Date(timestamp);
}
}
static class ReleasedAt extends Source {
ReleasedAt(@CheckForNull Throwable callSite) {
super(callSite);
}
@Override
public String toString() {
return " Released at "+new Date(timestamp);
}
}
/**
* Captures the list of export, so that they can be unexported later.
* This is tied to a particular thread, so it only records operations
* on the current thread.
* The class is not serializable.
*/
@Restricted(NoExternalUse.class)
@SuppressFBWarnings(value = "SE_BAD_FIELD_INNER_CLASS",
justification = "ExportList is supposed to be serializable as ArrayList, but it is not. "
+ "The issue is ignored since the class does not belong to the public API")
public final class ExportList extends ArrayList<Entry> {
private final ExportList old;
private ExportList() {
old=lists.get();
lists.set(this);
}
void release(Throwable callSite) {
synchronized(ExportTable.this) {
for (Entry e : this)
e.release(callSite);
}
}
void stopRecording() {
lists.set(old);
}
private static final long serialVersionUID = 1L; // we don't actually serialize this class but just to shutup FindBugs
}
/**
* Unique ID generator.
*/
private int iota = 1;
/**
* Starts the recording of the export operations
* and returns the list that captures the result.
*
* @see ExportList#stopRecording()
*/
ExportList startRecording() {
ExportList el = new ExportList();
lists.set(el);
return el;
}
boolean isRecording() {
return lists.get()!=null;
}
/**
* Exports the given object.
*
* <p>
* Until the object is {@link #unexport(Object,Throwable) unexported}, it will
* not be subject to GC.
*
* @return
* The assigned 'object ID'. If the object is already exported,
* it will return the ID already assigned to it.
* {@code 0} if the input parameter is {@code null}.
* @param clazz Class of the object
* @param t Class instance
*/
synchronized <T> int export(@Nonnull Class<T> clazz, @CheckForNull T t) {
return export(clazz, t,true);
}
/**
* Exports the given object.
* @param clazz Class of the object
* @param t Object to be exported
* @param notifyListener
* If false, listener will not be notified. This is used to
* @return
* The assigned 'object ID'. If the object is already exported,
* it will return the ID already assigned to it.
* {@code 0} if the input parameter is {@code null}.
*/
synchronized <T> int export(@Nonnull Class<T> clazz, @CheckForNull T t, boolean notifyListener) {
if(t==null) return 0; // bootstrap classloader
Entry e = reverse.get(t);
if (e == null) {
e = new Entry<T>(t, clazz);
} else {
e.addInterface(clazz);
}
e.addRef();
if(notifyListener) {
ExportList l = lists.get();
if(l!=null) l.add(e);
}
return e.id;
}
/*package*/ synchronized void pin(@Nonnull Object t) {
Entry e = reverse.get(t);
if(e!=null)
e.pin();
}
/**
* Retrieves object by id.
* @param id Object ID
* @return Object
* @throws ExecutionException The requested ID cannot be found.
* The root cause will be diagnosed by {@link #diagnoseInvalidObjectId(int)}.
*/
@Nonnull
synchronized Object get(int id) throws ExecutionException {
Entry e = table.get(id);
if(e!=null) return e.object;
throw diagnoseInvalidObjectId(id);
}
/**
* Retrieves object by id.
* @param oid Object ID
* @return Object or {@code null} if the ID is missing in the {@link ExportTable}.
* @since TODO
*/
@CheckForNull
synchronized Object getOrNull(int oid) {
Entry<?> e = table.get(oid);
if(e!=null) return e.object;
return null;
}
@Nonnull
synchronized Class[] type(int id) throws ExecutionException {
Entry e = table.get(id);
if(e!=null) return e.getInterfaces();
throw diagnoseInvalidObjectId(id);
}
/**
* Propagate a channel termination error to all the exported objects.
*
* <p>
* Exported {@link Pipe}s are vulnerable to infinite blocking
* when the channel is lost and the sender side is cut off. The reader
* end will not see that the writer has disappeared.
*
* @param e Termination error
*
*/
void abort(@CheckForNull Throwable e) {
List<Entry<?>> values;
synchronized (this) {
values = new ArrayList<Entry<?>>(table.values());
}
for (Entry<?> v : values) {
if (v.object instanceof ErrorPropagatingOutputStream) {
try {
((ErrorPropagatingOutputStream)v.object).error(e);
} catch (Throwable x) {
LOGGER.log(INFO, "Failed to propagate a channel termination error",x);
}
}
}
// clear the references to allow exported objects to get GCed.
// don't bother putting them into #unexportLog because this channel
// is forever closed.
synchronized (this) {
table.clear();
reverse.clear();
}
}
/**
* Creates a diagnostic exception for Invalid object id.
* @param id Object ID
* @return Exception to be thrown
*/
@Nonnull
private synchronized ExecutionException diagnoseInvalidObjectId(int id) {
Exception cause=null;
if (!unexportLog.isEmpty()) {
for (Entry e : unexportLog) {
if (e.id==id)
cause = new Exception("Object was recently deallocated\n"+Util.indent(e.dump()), e.releaseTrace);
}
if (cause==null)
cause = new Exception("Object appears to be deallocated at lease before "+
new Date(unexportLog.get(0).releaseTrace.timestamp));
}
return new ExecutionException("Invalid object ID "+id+" iota="+iota, cause);
}
/**
* Removes the exported object from the table.
* @param t Object to be unexported. {@code null} instances will be ignored.
* @param callSite Stacktrace of the invocation source
*/
synchronized void unexport(@CheckForNull Object t, Throwable callSite) {
if(t==null) return;
Entry e = reverse.get(t);
if(e==null) {
LOGGER.log(SEVERE, "Trying to unexport an object that's not exported: "+t);
return;
}
e.release(callSite);
}
/**
* Removes the exported object for the specified oid from the table.
* Logs error if the object has been already unexported.
*/
void unexportByOid(Integer oid, Throwable callSite) {
unexportByOid(oid, callSite, true);
}
/**
* Removes the exported object for the specified oid from the table.
* @param oid Object ID. If {@code null} the method will do nothing.
* @param callSite Unexport command caller
* @param severeErrorIfMissing Consider missing object as {@link #SEVERE} error. {@link #FINE} otherwise
* @since TODO
*/
synchronized void unexportByOid(@CheckForNull Integer oid, @CheckForNull Throwable callSite, boolean severeErrorIfMissing) {
if(oid==null) return;
Entry e = table.get(oid);
if(e==null) {
Level loggingLevel = severeErrorIfMissing ? SEVERE : FINE;
LOGGER.log(loggingLevel, "Trying to unexport an object that's already unexported", diagnoseInvalidObjectId(oid));
if (callSite!=null)
LOGGER.log(loggingLevel, "2nd unexport attempt is here", callSite);
return;
}
e.release(callSite);
}
/**
* Dumps the contents of the table to a file.
* @throws IOException Output error
*/
synchronized void dump(@Nonnull PrintWriter w) throws IOException {
for (Entry e : table.values()) {
e.dump(w);
}
}
/*package*/ synchronized boolean isExported(Object o) {
return reverse.containsKey(o);
}
/**
* Defines number of entries to be stored in the unexport history.
* @since 2.40
*/
public static int UNEXPORT_LOG_SIZE = Integer.getInteger(ExportTable.class.getName()+".unexportLogSize",1024);
private static final Logger LOGGER = Logger.getLogger(ExportTable.class.getName());
}