When transferring files in a Multipeer Session, using the Progress instances (returned by either sendResource in the sender or the delegate method session(didStartReceiving:) on the receiver) in a SwiftUI ProgressView will eventually cause a crash (EXC_BAD_ACCESS in swift_retain on com.apple.MCSession.syncQueue)
I have created a small sample project that demonstrates the problem. It can be found at: https://github.com/eidria/Multipeer-Progress-Demo.git. A screen shot of the stack trace from a crash (crash.jpg) is in the “Images” folder.
STEPS TO REPRODUCE Run the sample on two different hosts connected to the same network (project contains both iOS & macOS targets, bug manifests in any combination). When the second instance comes up, they will automatically find and connect to each other. When the “Send Files” button is enabled, clicking it will cause the sender to repeatedly send the file “Image.HEIC” from the “Images” folder to the receiver, which deletes it upon receipt of a successful transfer (i.e. delegate call back is called with a nil error). Subsequent transfers are triggered when the sender receives notice that the prior send completed successfully. Eventually, after some (usually small) number of files have been transferred, either the sender or receiver will crash in the middle of a transfer, with EXC_BAD_ACCESS in swift_retain on com.apple.MCSession.syncQueue.
Commenting out the ProgressView in the file FileTransferView.swift will allow the apps to run in perpetuity.
Hi @navvadassity,
I believe this is the result of a system bug involving either ProgressView (defined as @preconcurrency), Progress (defined as @unchecked Sendable) and Swift Concurrency (e.g., async tasks). Please submit a bug report via Feedback Assistant and respond here with the Feedback ID.
In addition, please ensure your report includes the description above, including the source code for the demo app screenshots and error logs uploaded as attachments.
Cheers,
Paris X Pinkney | WWDR | DTS Engineer
