Schedulers & Threading

Control which threads execute different parts of your reactive pipeline.

Scheduler Types

// Different schedulers for different purposes
Flux<Integer> flux = Flux.range(1, 10);

// Immediate (current thread)
flux.subscribeOn(Schedulers.immediate());

// Single (one dedicated thread)
flux.subscribeOn(Schedulers.single());

// Parallel (fixed worker pool)
flux.parallel()
    .runOn(Schedulers.parallel())
    .subscribe();

// Bounded elastic (for blocking operations)
Mono.fromCallable(() -> blockingIO())
    .subscribeOn(Schedulers.boundedElastic())
    .subscribe();

// Custom scheduler
Scheduler customScheduler = Schedulers.newBoundedElastic(
    10, 100, "custom-pool");

Threading Models

graph TB
    A[Publisher] --> B[subscribeOn]
    B --> C[Scheduler Pool]
    C --> D[Operator 1]
    D --> E[publishOn]
    E --> F[Different Scheduler]
    F --> G[Operator 2]
    G --> H[Subscriber]

subscribeOn vs publishOn

Flux.range(1, 5)
    .subscribeOn(Schedulers.parallel())     // Affects entire chain
    .map(i -> i * 2)                        // Runs on parallel thread
    .publishOn(Schedulers.boundedElastic()) // Changes thread from here
    .map(i -> i + 1)                        // Runs on bounded elastic
    .subscribe();

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