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concurrency

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A p99 latency spike to 800ms caused by a stop-the-world garbage collection pause, beside generational and concurrent collectors that shrink the stop by spending CPU to avoid it

ConcurrencyDay 58Sep 29, 2026

The Pause Nobody Scheduled

system-design concurrency garbage-collection

Two threads reading 41 and both writing 42 so one increment vanishes, beside a lock that makes threads queue and a compare-and-swap instruction that retries on collision instead of blocking

ConcurrencyDay 57Sep 28, 2026

Don't Take The Lock. Ask Instead.

system-design concurrency locks

Four CPU-bound Python threads funnelled into a single lane by the GIL against I/O-bound threads that release it while waiting, with processes and C extensions as the routes to real parallelism

ConcurrencyDay 56Sep 27, 2026

Four Cores, One Lane

system-design concurrency python

A sequential async method compiled into a state machine that releases its thread at every await and keeps locals on the heap, beside C# rewriting the code and Java rewriting the runtime

ConcurrencyDay 55Sep 26, 2026

The Keyword That Rewrites Our Method

system-design concurrency async-await

Platform threads carrying a megabyte of OS stack each against virtual threads parked on the heap by the Java runtime, letting plain sequential blocking code scale to millions of concurrent requests

ConcurrencyDay 54Sep 25, 2026

Threads That Cost Almost Nothing

system-design concurrency java

Ten thousand threads holding a megabyte of stack each while asleep, against one event loop asking the kernel which sockets have data ready, and the rule that nothing in a handler may ever block

ConcurrencyDay 53Sep 24, 2026

One Thread, Ten Thousand Connections

system-design concurrency event-loop

More Threads, Slower System — system design card, day 14, concurrency

ConcurrencyDay 14Aug 14, 2026

More Threads, Slower System

concurrency context-switching system-design

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