Package io.netty.util

Class ResourceLeakDetector.DefaultResourceLeak<T>

java.lang.Object

java.lang.ref.Reference<Object>

java.lang.ref.WeakReference<Object>

io.netty.util.ResourceLeakDetector.DefaultResourceLeak<T>

All Implemented Interfaces:

ResourceLeak, ResourceLeakTracker<T>

Enclosing class:

ResourceLeakDetector<T>

private static final class ResourceLeakDetector.DefaultResourceLeak<T>
extends WeakReference<Object>
implements ResourceLeakTracker<T>, ResourceLeak

Field Summary

Fields

Modifier and Type	Field	Description
private final Set<ResourceLeakDetector.DefaultResourceLeak<?>>	allLeaks
private int	droppedRecords
private static final AtomicIntegerFieldUpdater<ResourceLeakDetector.DefaultResourceLeak<?>>	droppedRecordsUpdater
private ResourceLeakDetector.TraceRecord	head
private static final AtomicReferenceFieldUpdater<ResourceLeakDetector.DefaultResourceLeak<?>,ResourceLeakDetector.TraceRecord>	headUpdater
private final int	trackedHash

Constructor Summary

Constructors

Constructor	Description
DefaultResourceLeak(Object referent, ReferenceQueue<Object> refQueue, Set<ResourceLeakDetector.DefaultResourceLeak<?>> allLeaks, Object initialHint)

Method Summary

Modifier and Type	Method	Description
boolean	close()	Close the leak so that ResourceLeakDetector does not warn about leaked resources.
boolean	close(T trackedObject)	Close the leak so that ResourceLeakTracker does not warn about leaked resources.
(package private) boolean	dispose()
private String	generateReport(ResourceLeakDetector.TraceRecord oldHead)
(package private) String	getReportAndClearRecords()
private static void	reachabilityFence0(Object ref)	Ensures that the object referenced by the given reference remains strongly reachable, regardless of any prior actions of the program that might otherwise cause the object to become unreachable; thus, the referenced object is not reclaimable by garbage collection at least until after the invocation of this method.
void	record()	Records the caller's current stack trace so that the ResourceLeakDetector can tell where the leaked resource was accessed lastly.
void	record(Object hint)	Records the caller's current stack trace and the specified additional arbitrary information so that the ResourceLeakDetector can tell where the leaked resource was accessed lastly.
private void	record0(Object hint)	This method works by exponentially backing off as more records are present in the stack.
String	toString()

Methods inherited from class java.lang.ref.Reference

clear, clone, enqueue, get, isEnqueued, reachabilityFence, refersTo

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Details

headUpdater

private static final AtomicReferenceFieldUpdater<ResourceLeakDetector.DefaultResourceLeak<?>,ResourceLeakDetector.TraceRecord> headUpdater

droppedRecordsUpdater

private static final AtomicIntegerFieldUpdater<ResourceLeakDetector.DefaultResourceLeak<?>> droppedRecordsUpdater

head

private volatile ResourceLeakDetector.TraceRecord head

droppedRecords

private volatile int droppedRecords

allLeaks

private final Set<ResourceLeakDetector.DefaultResourceLeak<?>> allLeaks

trackedHash

private final int trackedHash

Constructor Details

DefaultResourceLeak

DefaultResourceLeak(Object referent,
 ReferenceQueue<Object> refQueue,
 Set<ResourceLeakDetector.DefaultResourceLeak<?>> allLeaks,
 Object initialHint)

Method Details

record

public void record()

Description copied from interface: ResourceLeakTracker

Records the caller's current stack trace so that the ResourceLeakDetector can tell where the leaked resource was accessed lastly. This method is a shortcut to record(null).

Specified by:

record in interface ResourceLeak

Specified by:

record in interface ResourceLeakTracker<T>

record

public void record(Object hint)

Description copied from interface: ResourceLeakTracker

Records the caller's current stack trace and the specified additional arbitrary information so that the ResourceLeakDetector can tell where the leaked resource was accessed lastly.

Specified by:

record in interface ResourceLeak

Specified by:

record in interface ResourceLeakTracker<T>

record0

private void record0(Object hint)

This method works by exponentially backing off as more records are present in the stack. Each record has a 1 / 2^n chance of dropping the top most record and replacing it with itself. This has a number of convenient properties:

1. The current record is always recorded. This is due to the compare and swap dropping the top most record, rather than the to-be-pushed record.
2. The very last access will always be recorded. This comes as a property of 1.
3. It is possible to retain more records than the target, based upon the probability distribution.
4. It is easy to keep a precise record of the number of elements in the stack, since each element has to know how tall the stack is.

In this particular implementation, there are also some advantages. A thread local random is used to decide if something should be recorded. This means that if there is a deterministic access pattern, it is now possible to see what other accesses occur, rather than always dropping them. Second, after ResourceLeakDetector.TARGET_RECORDS accesses, backoff occurs. This matches typical access patterns, where there are either a high number of accesses (i.e. a cached buffer), or low (an ephemeral buffer), but not many in between. The use of atomics avoids serializing a high number of accesses, when most of the records will be thrown away. High contention only happens when there are very few existing records, which is only likely when the object isn't shared! If this is a problem, the loop can be aborted and the record dropped, because another thread won the race.

dispose

boolean dispose()

close

public boolean close()

Description copied from interface: ResourceLeak

Close the leak so that ResourceLeakDetector does not warn about leaked resources.

Specified by:

close in interface ResourceLeak

Returns:

true if called first time, false if called already

close

public boolean close(T trackedObject)

Description copied from interface: ResourceLeakTracker

Close the leak so that ResourceLeakTracker does not warn about leaked resources. After this method is called a leak associated with this ResourceLeakTracker should not be reported.

Specified by:

close in interface ResourceLeakTracker<T>

Returns:

true if called first time, false if called already

reachabilityFence0

private static void reachabilityFence0(Object ref)

Ensures that the object referenced by the given reference remains strongly reachable, regardless of any prior actions of the program that might otherwise cause the object to become unreachable; thus, the referenced object is not reclaimable by garbage collection at least until after the invocation of this method.

Recent versions of the JDK have a nasty habit of prematurely deciding objects are unreachable. see: https://stackoverflow.com/questions/26642153/finalize-called-on-strongly-reachable-object-in-java-8 The Java 9 method Reference.reachabilityFence offers a solution to this problem.

This method is always implemented as a synchronization on ref, not as Reference.reachabilityFence for consistency across platforms and to allow building on JDK 6-8. It is the caller's responsibility to ensure that this synchronization will not cause deadlock.

Parameters:

ref - the reference. If null, this method has no effect.

See Also:

• Reference.reachabilityFence(java.lang.Object)

toString

public String toString()

Overrides:

toString in class Object

getReportAndClearRecords

String getReportAndClearRecords()

generateReport

private String generateReport(ResourceLeakDetector.TraceRecord oldHead)