Crash with Deployment on mobile device

[Boya-Na]

Hi,

• Have I written custom code (as opposed to running examples on an unmodified clone of the repository): yes, but just add the wrapper to call streaming related API
• OS Platform and Distribution (e.g., Linux Ubuntu 16.04): arm64 ios 11+ & android sdk 26+
• TensorFlow installed from (our builds, or upstream TensorFlow): DeepSpeech official build
• Bazel version (if compiling from source): 3.1.0

I use the official library for android and build the iOS framework followed by #3436

when call streaming-related functions (feedAudioContent, intermediateDetecode & finishStream) in different threads, it would crash sometimes. For example, in Android, when call feedAudioContent & intermediateDetecode in thread 1 then call finishStream in thread 2, the app would crash. The situation in iOS is similar, when API is called in different threads, it may crash

Is deep speech library thread-safe on mobile devices? How could it be fixed? Thanks so much!

[JanX2]

@Boya-Na Could you please check, if your crashes go away after merging #3527?