Threads vs Async: Has Asyncio Solved Concurrency? by Jacob Unna

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1 PyCon ZA 2020 Has Asyncio Solved Concurrency?

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2 Jacob Unna Software Engineer @ Deloitte Analytics & Cognitive [email protected] @JacobUnna

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3 What is Concurrency?

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4 Concurrency in Python − Threads − Asyncio

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5 Concurrency in Python − Threads − Asyncio − How do they work? − Which is better? − Does asyncio spell the end for threads?

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6 Scheduling

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7 Scheduling

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9 Cooperative Scheduling Asyncio

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10 Cooperative scheduling • Can be implemented at the application level • Everything must be non-blocking

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11 Cooperative scheduling • Can be implemented at the application level • Everything must be non-blocking Cooperation

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12 Preemptive Scheduling Threads

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13 Preemptive scheduling • Run any two bits of code at the same time • Handled by the operating system − Wouldn't be possible using pure Python − Operating system preempts running code i.e. freezes it mid-flow and switches the CPU's attention to something else • Doesn't get stuck on uncooperative code

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14 Today's Agenda − How do threads and asyncio work? − Which is better? − Does asyncio spell the end for threads?

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15 Which is better? Threads Asyncio Overhead when switching task High Low

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16 Which is better? Threads Asyncio Overhead when switching task High Low Easy to reason about No Yes

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17 Which is better? Threads Asyncio Overhead when switching task High Low Easy to reason about No Yes Handle blocking code Yes No

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18 Which is better? Threads Asyncio Overhead when switching task High Low Easy to reason about No Yes Handle blocking code Yes No

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19 Today's Agenda − How do threads and asyncio work? − Which is better? − Does asyncio spell the end for threads?

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20 Which is better? • Cheap • Safe • Easy to use • Can cut through solid wood

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21 Can I do this with asyncio? Decision flow Use asyncio Use threads Yes No

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22 Asyncio ≠ Cooperative Scheduling

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23 Because cooperative scheduling takes place at the application level, it is easy to create new frameworks

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24 Because cooperative scheduling takes place at the application level, it is easy to create new frameworks (Relative to creating a new operating system)