Open
Conversation
…r dispatcher Replace runBlocking with direct suspend calls in getDeviceScreen and takeScreenshot. Use Mutex instead of synchronized to support suspension within the critical section. This avoids tying up Ktor dispatcher threads on the SSE hot path.
pedro18x
approved these changes
Apr 14, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Summary
viewHierarchy(),deviceInfo(), andtakeScreenshot()callssynchronized(DeviceService)with coroutine Mutex - synchronized can't be used with suspend functions since it locks a thread, but a suspend function may resume on a different thread. Mutex provides the same mutual exclusion but suspends the coroutine instead of blocking the thread.Why
getDeviceScreenis called from the/api/device-screen/sseendpoint inside respondBytesWriter, which is already a suspend context. Using runBlocking here blocks a Ktor dispatcher thread for the duration of each device call. Under concurrent SSE connections, this ties up threads unnecessarily. Since all the underlying Maestro methods are already suspend (from #3162), we can just call them directly.