Package com.google.gerrit.server.cache

Class PerThreadCache

java.lang.Object

com.google.gerrit.server.cache.PerThreadCache

All Implemented Interfaces:

AutoCloseable

public class PerThreadCache
extends Object
implements AutoCloseable

Caches object instances for a request as ThreadLocal in the serving thread.

This class is intended to cache objects that have a high instantiation cost, are specific to the current request and potentially need to be instantiated multiple times while serving a request.

This is different from the key-value storage in CurrentUser: CurrentUser offers a key-value storage by providing thread-safe get and put methods. Once the value is retrieved through get there is not thread-safety anymore - apart from the retrieved object guarantees. Depending on the implementation of CurrentUser, it might be shared between the request serving thread as well as sub- or background treads.

In comparison to that, this class guarantees thread safety even on non-thread-safe objects as its cache is tied to the serving thread only. While allowing to cache non-thread-safe objects, it has the downside of not sharing any objects with background threads or executors.

Lastly, this class offers a cache, that requires callers to also provide a Supplier in case the object is not present in the cache, while CurrentUser provides a storage where just retrieving stored values is a valid operation.

To prevent OOM errors on requests that would cache a lot of objects, this class enforces an internal limit after which no new elements are cached. All get calls are served by invoking the Supplier after that.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	PerThreadCache.Key<T>	Unique key for key-value mappings stored in PerThreadCache.

Method Summary

Modifier and Type	Method	Description
void	close()
static PerThreadCache	create()
static PerThreadCache	get()
<T> T	get(PerThreadCache.Key<T> key, Supplier<T> loader)	Returns an instance of T that was either loaded from the cache or obtained from the provided Supplier.
static <T> T	getOrCompute(PerThreadCache.Key<T> key, Supplier<T> loader)

Methods inherited from class java.lang.Object

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

Method Detail

create

public static PerThreadCache create()

get

public static PerThreadCache get()

getOrCompute

public static <T> T getOrCompute(PerThreadCache.Key<T> key,
                                 Supplier<T> loader)

get

public <T> T get(PerThreadCache.Key<T> key,
                 Supplier<T> loader)

Returns an instance of T that was either loaded from the cache or obtained from the provided Supplier.

close

public void close()

Specified by:

close in interface AutoCloseable