The JavaScript heaps are distinct, that's true, but there is a single shared wasm heap which is used from multiple threads. That is enough to implement the pthr

The JavaScript heaps are distinct, that's true, but there is a single shared wasm heap which is used from multiple threads. That is enough to implement the pthreads API. Applications like Photoshop and Google Earth use ptheads on the Web so their compiled C++ is multithreaded, very similar to how it would run natively, and with similar responsiveness and throughput speedups. Though there are some limitations too, see https://emscripten.org/docs/porting/pthreads.html https://emscripten.org/docs/porting/pthreads.html