Structured Concurrency in Java: The what and the why

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Alignment indicator 29 June 2023 Balkrishna Rawool Structured Concurrency in Java The what and the why

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2 Balkrishna Rawool IT Chapter Lead, ING Bank @BalaRawool

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3 Project Loom Purpose: Ø Supporting easy-to-use, high-throughput lightweight concurrency and new programming models for it Features: Ø Virtual Threads: It will be finalized in Java 21 JEP - 444 Ø Structured Concurrency: Preview – JEP - 453 Ø Scoped Values: Preview – JEP - 446

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4 (Platform) Threads JVM OS Platform Threads Platform Threads: Ø Abstraction over OS threads Ø Limited scalability (when using thread-per-request model) Ø Need for pooling

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5 Virtual Threads JVM OS Platform Threads Virtual Threads: Ø Lightweight user threads Ø Highly scalable Ø No need for pooling Virtual Threads

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Alignment indicator How to create virtual threads? Demo

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7 Virtual Thread Scheduler Platform Thread Virtual Threads

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8 Virtual Threads continued… PT 1 VT 1 VT 2 VT 3 VT 4 VT 1 VT 1 VT 2 VT 2 VT 3 VT 3 VT 4 VT 4 VT 1 VT 2 VT 3 VT 1 VT 2 VT 4 VT 3 VT 4

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9 Use virtual threads to model (business) tasks.

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10 Virtual threads enable Structured Concurrency

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11 Programs → Structured Programming Concurrent programs → Structured Concurrency

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12 Structured Concurrency: Continued Principle: Ø When flow of execution splits into multiple concurrent flows, they rejoin in the same code block Benefits: Ø Error handling with short-circuiting Ø Cancellation propagation Ø Clarity Ø Observability

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13 Structured Concurrency: Examples All these can be modelled using StructuredTaskScope.

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14 CompletableFuture Ø Provides API for asynchronous processing Ø Chain multiple stages to create pipeline Ø Callbacks

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Alignment indicator CompletableFuture API vs Structured Concurrency API Demo

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16 Use case 1: Event Management Reserve Venue Book Hotel Buy Supplies

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17 Use case 2: Weather Service Get Weather From Source 1 Get Weather From Source 2 Get Weather From Source 3

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18 Use case 1: Banking Portal Get Savings Data Get Loans Data Get Customer Data Calculate Offer

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Shutdown policies Ø ShutdownOnFailure Stops when one of the tasks “fail” Cancels other tasks Useful when you want that all tasks must complete successfully Ø ShutdownOnSuccess Stops when one of the tasks “succeed” Cancels other tasks Useful when you want any one of the tasks to complete successfully Ø Custom Extend StructuredTaskScope Override handleComplete() Useful when you want custom logic/ some tasks to complete successfully 19

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Be aware of Pinning! 20 Ø When virtual thread is executing a synchronized code-block or method, it gets pinned Ø Problem if you’re doing long-running/ blocking operations inside synchronized Ø Identify cases with JFR (JDK Flight Recorder) Ø Use re-entrant lock

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Join us at 21 ing.jobs/tech

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Questions and Feedback 22 ? Contact points: @ balkrishna.rawool@ing.com @BalaRawool in/balkrishnarawool /balkrishnarawool

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