# subscribe(on:options:) Specifies the scheduler on which to perform subscribe, cancel, and request operations. ``` func subscribe(on scheduler: S, options: S.SchedulerOptions? = nil) -> Publishers.SubscribeOn where S : Scheduler ``` ## Parameters `scheduler` The scheduler used to send messages to upstream publishers. `options` Options that customize the delivery of elements. ## Return Value A publisher which performs upstream operations on the specified scheduler. ## Discussion In contrast with [`receive(on:options:)`](/documentation/Combine/Publisher/receive(on:options:)), which affects downstream messages, [`subscribe(on:options:)`](/documentation/Combine/Publisher/subscribe(on:options:)) changes the execution context of upstream messages. In the following example, the [`subscribe(on:options:)`](/documentation/Combine/Publisher/subscribe(on:options:)) operator causes `ioPerformingPublisher` to receive requests on `backgroundQueue`, while the [`receive(on:options:)`](/documentation/Combine/Publisher/receive(on:options:)) causes `uiUpdatingSubscriber` to receive elements and completion on `RunLoop.main`. ``` let ioPerformingPublisher == // Some publisher. let uiUpdatingSubscriber == // Some subscriber that updates the UI. ioPerformingPublisher .subscribe(on: backgroundQueue) .receive(on: RunLoop.main) .subscribe(uiUpdatingSubscriber) ``` Using [`subscribe(on:options:)`](/documentation/Combine/Publisher/subscribe(on:options:)) also causes the upstream publisher to perform [`cancel()`](/documentation/Combine/Cancellable/cancel()) using the specfied scheduler. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)