Package io.opentelemetry.context.internal.shaded

Class WeakConcurrentMap<K,V>

java.lang.Object

java.lang.ref.ReferenceQueue<K>

io.opentelemetry.context.internal.shaded.AbstractWeakConcurrentMap<K,V,WeakConcurrentMap.LookupKey<K>>

io.opentelemetry.context.internal.shaded.WeakConcurrentMap<K,V>

All Implemented Interfaces:

Iterable<Map.Entry<K,V>>, Runnable

Direct Known Subclasses:

StrictContextStorage.PendingScopes, WeakConcurrentMap.WithInlinedExpunction

public class WeakConcurrentMap<K,V>
extends AbstractWeakConcurrentMap<K,V,WeakConcurrentMap.LookupKey<K>>

A thread-safe map with weak keys. Entries are based on a key's system hash code and keys are considered equal only by reference equality. This class does not implement the Map interface because this implementation is incompatible with the map contract. While iterating over a map's entries, any key that has not passed iteration is referenced non-weakly.

This class has been copied as is from https://github.com/raphw/weak-lock-free/blob/ad0e5e0c04d4a31f9485bf12b89afbc9d75473b3/src/main/java/com/blogspot/mydailyjava/weaklockfree/WeakConcurrentMap.java

This class is internal and is hence not for public use. Its APIs are unstable and can change at any time.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
(package private) static final class	WeakConcurrentMap.LookupKey<K>
static class	WeakConcurrentMap.WithInlinedExpunction<K,V>	A WeakConcurrentMap where stale entries are removed as a side effect of interacting with this map.

Nested classes/interfaces inherited from class io.opentelemetry.context.internal.shaded.AbstractWeakConcurrentMap

AbstractWeakConcurrentMap.WeakKey<K>

Field Summary

Fields

Modifier and Type	Field	Description
private static final AtomicLong	ID
private static final ThreadLocal<WeakConcurrentMap.LookupKey<?>>	LOOKUP_KEY_CACHE	Lookup keys are cached thread-locally to avoid allocations on lookups.
private final boolean	reuseKeys
private final Thread	thread

Fields inherited from class io.opentelemetry.context.internal.shaded.AbstractWeakConcurrentMap

target

Constructor Summary

Constructors

Constructor	Description
WeakConcurrentMap(boolean cleanerThread)
WeakConcurrentMap(boolean cleanerThread, boolean reuseKeys)
WeakConcurrentMap(boolean cleanerThread, boolean reuseKeys, ConcurrentMap<AbstractWeakConcurrentMap.WeakKey<K>,V> target)

Method Summary

Modifier and Type	Method	Description
Thread	getCleanerThread()
protected WeakConcurrentMap.LookupKey<K>	getLookupKey(K key)	Override with care as it can cause lookup failures if done incorrectly.
private static boolean	isPersistentClassLoader(ClassLoader classLoader)	Checks whether the provided ClassLoader may be unloaded like a web application class loader, for example.
protected void	resetLookupKey(WeakConcurrentMap.LookupKey<K> lookupKey)	Resets any reusable state in the lookup key.

Methods inherited from class io.opentelemetry.context.internal.shaded.AbstractWeakConcurrentMap

approximateSize, clear, containsKey, defaultValue, expungeStaleEntries, get, getIfPresent, iterator, put, putIfAbsent, putIfProbablyAbsent, remove, run, toString

Methods inherited from class java.lang.ref.ReferenceQueue

poll, remove, remove

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Field Details

LOOKUP_KEY_CACHE

private static final ThreadLocal<WeakConcurrentMap.LookupKey<?>> LOOKUP_KEY_CACHE

Lookup keys are cached thread-locally to avoid allocations on lookups. This is beneficial as the JIT unfortunately can't reliably replace the WeakConcurrentMap.LookupKey allocation with stack allocations, even though the WeakConcurrentMap.LookupKey does not escape.

ID

private static final AtomicLong ID

thread

private final Thread thread

reuseKeys

private final boolean reuseKeys

Constructor Details

WeakConcurrentMap

public WeakConcurrentMap(boolean cleanerThread)

Parameters:

cleanerThread - true if a thread should be started that removes stale entries.

WeakConcurrentMap

public WeakConcurrentMap(boolean cleanerThread,
 boolean reuseKeys)

Parameters:

cleanerThread - true if a thread should be started that removes stale entries.

reuseKeys - true if the lookup keys should be reused via a ThreadLocal. Note that setting this to true may result in class loader leaks. See isPersistentClassLoader(ClassLoader) for more details.

WeakConcurrentMap

public WeakConcurrentMap(boolean cleanerThread,
 boolean reuseKeys,
 ConcurrentMap<AbstractWeakConcurrentMap.WeakKey<K>,V> target)

Parameters:

cleanerThread - true if a thread should be started that removes stale entries.

reuseKeys - true if the lookup keys should be reused via a ThreadLocal. Note that setting this to true may result in class loader leaks. See isPersistentClassLoader(ClassLoader) for more details.

target - ConcurrentMap implementation that this class wraps.

Method Details

isPersistentClassLoader

private static boolean isPersistentClassLoader(ClassLoader classLoader)

Checks whether the provided ClassLoader may be unloaded like a web application class loader, for example.

If the class loader can't be unloaded, it is safe to use ThreadLocals and to reuse the WeakConcurrentMap.LookupKey. Otherwise, the use of ThreadLocals may lead to class loader leaks as it prevents the class loader this class is loaded by to unload.

Parameters:

classLoader - The class loader to check.

Returns:

true if the provided class loader can be unloaded.

getLookupKey

protected WeakConcurrentMap.LookupKey<K> getLookupKey(K key)

Description copied from class: AbstractWeakConcurrentMap

Override with care as it can cause lookup failures if done incorrectly. The result must have the same Object.hashCode() as the input and be equal to a weak reference of the key. When overriding this, also override AbstractWeakConcurrentMap.resetLookupKey(L).

Specified by:

getLookupKey in class AbstractWeakConcurrentMap<K,V,WeakConcurrentMap.LookupKey<K>>

resetLookupKey

protected void resetLookupKey(WeakConcurrentMap.LookupKey<K> lookupKey)

Description copied from class: AbstractWeakConcurrentMap

Resets any reusable state in the lookup key.

Specified by:

resetLookupKey in class AbstractWeakConcurrentMap<K,V,WeakConcurrentMap.LookupKey<K>>

getCleanerThread

public Thread getCleanerThread()

Returns:

The cleaner thread or null if no such thread was set.