The WebNN graph building (MLGraphBuilder.build) and execution (MLGraph.compute) are sync APIs. This is required to implement a backend for Wasm-based ML frameworks, such as ONNX Runtime Execution Provider, TensorFlow Lite Delegate and OpenCV.js DNN backend. These frameworks are written in C++ and expect calling synchronous APIs in its backend implementation. To avoid blocking the main thread, the good practice is to call these synchronous APIs in a worker context.

The sync APIs are now exposed in both Window and DedicatedWorker. Should WebNN spec restrict the sync APIs to only exist in workers?

/cc @jyasskin