// Concurrency/parallelism patterns: race prevention, deadlock avoidance, message passing, async/channels/mutexes/worker pools.
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Document architectural decisions using ADR format. Use during research when choosing approaches, introducing deps/patterns, or changing arch.
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| name | concurrency-and-threading-principles |
| description | Concurrency/parallelism patterns: race prevention, deadlock avoidance, message passing, async/channels/mutexes/worker pools. |
| user-invocable | false |
Multiple threads + shared data + write + no sync = race.
Prevention: locks/mutexes, immutability, message passing, thread-local storage.
Detection: Go=-race, Rust=Miri, C/C++=TSan, Java=JCStress/FindBugs.
Two+ threads waiting for each other. Four conditions (ALL required): mutual exclusion, hold-and-wait, no preemption, circular wait.
Prevention (break any one): lock ordering (same order always), try_lock with timeout, avoid nested locks, lock-free data structures.
Immutable = thread-safe. No sync needed. Share freely. If must change → message passing.
"Share memory by communicating" (Go proverb). Channels/queues instead of shared memory. Reduces lock need. Easier to reason about and test.
Timeouts, retries, circuit breakers. Don't crash app on one thread failure. Supervisors for fault tolerance. Backpressure for producer-consumer.
