Guava Overview Part 2 Bucharest JUG #2

Guava Overview. Part 2 Andrei Savu / Bucharest JUG #2 asavu @ axemblr.com

About meFounding Partner @ Axemblr.comApache Whirr PMC Memberjclouds committerConnect with me on LinkedIn

@ AxemblrBuilding a tool and a platform for managingApache Hadoop clusters on cloud infrastructureAxemblr Tool for Cloudera CDH3 http://axemblr.com/toolAxemblr Service for Apache Hadoop http://axemblr.com/service

Plan● What is Guava?● Caches● Concurrency Services

Quick Intro

What is Guava?Open-source version of Googles core Javalibraries[...] carefully designed, tested, optimized andused in production at GoogleYou dont need to write them, test them, oroptimize them: you can just use them.

What is Guava? (cont)Battle-tested in production at GoogleStaggering numbers of unit tests. >110.000 asof January 2012 (generated)Lives near the bottom of the stack, right on topof the JDK itself

Caches

Caches - When to use?When a value is either● expensive to compute● expensive to retrieveMore or less similar to ConcurrentMap +automatic eviction

Caches - When to use? (cont)● spend memory to improve speed● keys are queried multiple times● your application would work if every value was evicted immediately● you have less data than RAM

Caches - Example #1

Caches - Example #2

Caches - Example #3cache.put(key, value)A Cache can be accessed as a Map:Cache.asMap() returns a ConcurrentMap

Caches - Eviction #1By size CacheBuilder.maximumSize(long)By custom weight CacheBuilder.weigher(Weigher) CacheBuilder.maximumWeight(long)

Caches - Eviction #2By time expireAfterAccess(long, TimeUnit) expireAfterWrite(long, TimeUnit)

Caches - Eviction #3Reference-based eviction CacheBuilder.weakKeys() CacheBuilder.weakValues() CacheBuilder.softValues()Note: all of them are using == for equality and*not* equals()

Caches - Eviction #4Explicit Cache.invalidate(key) Cache.invalidateAll(keys) Cache.invalidateAll()

Caches - Removal ListenersCacheBuilder .removalListener(RemovalListener)Be aware of long running listeners. They areblocking the queue.RemovalListeners .asynchronous(RemovalListener, Executor)

Caches - CleanupAutomatic eviction happens on writesExplicit Cache.cleanup()(you can put this in a thread)

Caches - RefreshLoadingCache.refresh(K)CacheLoader.reload(K, V)(if the new value can be computed from the oldone)

Cache - StatisticsCacheBuilder.recordStats()CacheStats Cache.stats() hitRate() averageLoadPenalty() evictionCount()

Service

What is this?Object with operational stateStart and stop methodsE.g. web servers, RPC servers, timers etc.Non-trivial if multiple threads are involved.

Lifecycle● Service.State.NEW to● Service.State.STARTING to● Service.State.RUNNING to● Service.State.STOPPING to● Service.State.TERMINATEDOn failure:● Service.State.FAILEDA stopped service may not be restarted.

Lifecycle #2asynchronously: start - returns ListenableFuture stopsynchronously startAndWait stopAndWait

Implementations

AbstractIdleServiceHas nothing to run:

AbstractExecutionThreadService

AbstractScheduledServiceSimilar to AbstractExecutionThreadServiceOverride runOneIterationImplement scheduler() newFixedRateSchedule(initialDelay, delay,TimeUnit) newFixedDelaySchedule(initialDelay, delay,TimeUnit)

Next?Functional IdiomsRangesI/OHashingMathReflectionConcurrency (ListenableFuture)EventBusSee Guava Wiki

Thanks! Questions?Andrei Savu / asavu @ axemblr.com

Guava Overview Part 2 Bucharest JUG #2

by Andrei Savu on Jun 21, 2012

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