C API Thread-Safety

[sbodenstein]

Applications using the C API sometimes require knowledge of the thread-safety of the functions in the C API. For example, it can be useful for a client to run MXNDArrayWaitAll in a separate thread so that the master client thread is free whilst waiting for MXNet to complete its computations.

Could the thread-safety be made official (if the implementation is thread-safe), which means documenting and testing thread-safety (particularly the waiting functions MXNDArrayWaitAll, MXNDArrayWaitToWrite and MXNDArrayWaitToRead)?

[anirudhacharya]

@mxnet-label-bot [C API, Thread Safety]