Julia Threads

Julia Threads

Use Julia Base.Threads tools to parallelize CPU work while preserving thread safety.

Start Julia with the Right Thread Configuration

Use CLI flags or env vars before launch:

julia --threads 4
export JULIA_NUM_THREADS=4

Check runtime layout:

Threads.nthreads(:default)
Threads.nthreads(:interactive)
Threads.threadid()

Use threadpools for responsiveness and interactive tasks.

Pick the Execution Primitive

• Use Threads.@threads for parallel loops over iteration spaces.
• Use Threads.@spawn for task-based parallel decomposition.
• Use @spawn :interactive ... for latency-sensitive tasks.

For reduction-style work, avoid shared mutable accumulators; split work into independent chunks and combine results after fetch.

Enforce Data-Race Freedom

Treat race freedom as a hard requirement:

• Protect shared mutable state with ReentrantLock, @lock, or lock(... do ...).
• Prefer Base.Lockable to bind lock + protected object.
• Use Threads.Atomic / atomic_* for primitive shared counters and similar patterns.
• Use per-field atomics (@atomic, @atomicswap, @atomicreplace, @atomiconce) when field-level ordering is required.

Handle Migration and Runtime Caveats

• Do not assume threadid() stays constant inside a task.
• Avoid per-thread buffers indexed by threadid() unless migration constraints are handled.
• Expect @spawn scheduling order to be nondeterministic.
• Insert GC.safepoint() in long compute-bound loops if needed to prevent GC starvation.
• Avoid parallel top-level include/eval of types/modules/methods.

Reference

• references/threading-patterns.md - thread setup, safety, and synchronization patterns

Related Skills

• julia-async - task/channel concurrency and event scheduling
• julia-tests - validating threaded behavior in tests

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Krastanov
• Source: Krastanov/JuliaLLMAgentSkills
• License: Unlicense

Install and usage instructions live in the source repository linked above.