kp-channels

One-line summary

A Channel<T> is a coroutine-safe queue used for message-passing between coroutines — the building block for pipelines, fan-out / fan-in, and any coordination that can't be expressed with Flow or shared state alone.

When to use this skill

• Multiple producer coroutines or multiple consumer coroutines that need to coordinate on a stream of values.
• Building a pipeline: stage A produces; stage B transforms; stage C writes. Each stage is its own coroutine connected by channels.
• Fan-out: one producer, many workers (load distribution).
• Fan-in: many producers, one consumer (collecting results).
• When Flow is too constrained — Flow is single-collector-cold; Channel lets multiple coroutines compete for elements.

When NOT to use this skill

• A single producer and a single consumer with no buffering needs → just use a Flow (cold) or suspend fun.
• Sharing observable state with multiple subscribers → StateFlow / SharedFlow (see kp-flow-cold-vs-hot).
• Pure transformations on a stream → Flow operators (see kp-flow-operators).
• Coordination between threads in non-coroutine code → use a java.util.concurrent queue.