Support time.sleep

[rth]

As mentioned in #97

noticed that time.sleep() is a no op in the pyodide's cpython webassembly runtime. As cpython implements it using select.select()'s timeout, it's not really a surprise that it's not supported by pyodide.

It would be good to provide a different implementation for time.sleep since sync code cannot use await asyncio.sleep

For instance, emscripten's musl has __clock_nanosleep but this might need threading enabled.

Other possible solutions were discussed in #97

[rth]

I haven't looked too long at it previously (and could be wrong) but as far as I understand it's a problem that is harder than it sounds essentially the same as sync IO and #2664. Because

• if we could have time.sleep working (and allowing other tasks on the event loop to run) we could convert an async call to sync by polling with something like,

  future = asyncio.run_coroutine_threadsafe(coro, loop)
  while not future.done():
      sleep(duration)

• and the other way around if we had the ability to call async functions inside sync functions we could just use asyncio.sleep here

For instance emscripten_sleep requires asyncify

xref pyscript/pyscript#324 cc @antocuni

[antocuni]

Right, I think I overlooked the problem and I agree that it's basically as hard as sync IO. The discussion is a bit hard to follow because it's spread out into many slightly-different-but-related issues; my comment on the pyscript issue might be relevant, because it shows why solutions like unthrow doesn't work IMHO:
pyscript/pyscript#324 (comment)

[joemarshall]

I just chucked an example solution using atomics in #3142. Works without cross site isolation too.

[ryanking13]

Emscripten now uses busy wait for time.sleep. Closing as resolved.