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Java concurrency in practice

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Every Java developer knows that multithreading is the root of all evil and it is quite hard to write correct code for concurrent environment. But what tasks do exist in real commercial development except running code in asynchronous way? In this talk I will present several tasks from my real projects and solutions we designed for them. This talk is very application oriented and allows participants to extend their vision of concurrent programming.

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Concurrency in practice Mikalai Alimenkou http://xpinjection.com @xpinjection

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Java concurrency in practice

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Disclaimer This is all my personal experience

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You could follow my slides http://slidesha.re/1vCS9dx

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Lets start from practical tasks!

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Java concurrency in practice

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#1. Graceful shutdown SERVICE 1 SERVICE 2 DB async jobs long batch operations

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Shared boolean flag

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#2. Retry on error task

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Configurable retry until done

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#3. Concurrent task executor TASK EXECUTOR SERVICE add task wait for tasks completion

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Submit tasks in single thread

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Limit concurrent tasks

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Wait for single or all tasks

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Get results and reduce count

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#4. Resource locking RESOURCE A THREAD 1 THREAD 2 WAIT THREAD 3 RESOURCE B

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Simple map to store locks

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Count lock usages to remove it

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Reduce synchronization penalty

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#5. Inter-process named locks RESOURCE THREAD 1 THREAD 2 THREAD 3 WAIT WAIT PROCESS 1 PROCESS 2

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Locks are stored in simple map

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On error throw own exception

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#6. Limit resource access rate RESOURCE THREAD 1 THREAD 2 WAIT THREAD 1 THREAD 2 3 REQ/SEC

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Use Semaphore as limiter

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Work with current semaphore

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Reset not used semaphores

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#7. Transparent batching TASK EXECUTOR THREAD 1 add task wait for results THREAD 2 THREAD 3 wait for results add task add task wait for results

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Just add task to task executor

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Tasks processed in batches

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Wait for first item opening batch

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Take full batch for processing

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#8. Resource access control RESOURCE A THREAD 1 THREAD 2 ALLOW FORBID ALLOW THREAD 3 RESOURCE B

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Check if resource access allowed

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Access success is based on time

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Check for successful access

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#9. Sharded quick counters

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LongAdder algorithm

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Lets review useful tools!

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#1. Thread factory builder

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#2. ConcurrentUtils

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#3. TimedSemaphore

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#4. TimeLimiter

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#5. RateLimiter

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#6. Striped

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#7. ListenableFuture

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#8. Uninterruptibles

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#9. CLHQueueLock

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Spin lock implementation

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#10. Disruptor

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#11. ZooKeeper + Curator • Elections • Locks • Barriers • Counters • Caches • Nodes • Queues

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Useful links • https://code.google.com/p/guava-libraries/ • http://commons.apache.org/proper/commons-lang/ • http://dou.ua/lenta/articles/clh-lock/ • http://habrahabr.ru/company/luxoft/blog/157273/ • http://habrahabr.ru/post/130113/ • http://lmax-exchange.github.io/disruptor/ • http://zookeeper.apache.org/ • http://curator.apache.org/ • http://en.wikipedia.org/wiki/Ctrie • https://code.google.com/p/guava-libraries/wiki/ListenableFutureExplained • https://guava-libraries.googlecode.com/files/guava-concurrent-slides.pdf

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And remember…

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@xpinjection http://xpinjection.com mikalai.alimenkou@xpinjection.com

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