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0299-Avoid-Deadlock.md

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Add a Mechanism to Avoid Deadlock

Introduction

This proposal is to avoid deadlock by adding a mechanism that stops Audio Streaming under certain conditions when the app on the mobile device side moves to BACKGROUND.

Motivation

When using SDL Core 4.5, and SDL iOS (v6.3.1 or later), a deadlock may occur when Audio Streaming is played while Video Streaming is stopped. Due to this support (smartdevicelink/sdl_ios#1235) in the current SDL iOS (v6.3.1 or later), Audio Streaming continues to play when the app on the mobile device side moves to BACKGROUND. For this reason (#1235), a deadlock may occur. To avoid the deadlock, it is desirable to add a mechanism where the negotiated RPC spec version is judged by the iOS library and stops Audio Streaming when the app on the mobile device side moves to BACKGROUND.

Proposed solution

The negotiated RPC spec version and the manufacturer name are checked by the iOS library, when the app on the mobile device side moves to BACKGROUND. If the negotiated RPC spec version is 4.5.1 (used in SDL Core v4.5.2) or older and the manufacturer name is not Ford, then Audio Streaming is stopped.

Potential downsides

None

Impact on existing code

This will be a bugfix/patch version change to the iOS Library.

Alternatives considered

  • Update the modified SDL Core to head unit (HU) -> It will be difficult because updating the HU is not realistic.

  • Add an API, which sets whether to use Audio Streaming on the app side or not, to the library and supported by each app vendor -> Deadlock will still occur in unsupported apps because there is no way to enforce.