No thread yield when using synchronous processes?

[Philipp Stephani]

Hi,

it seems like Emacs doesn't yield when using synchronous processes:

(make-thread (lambda () (call-process "sleep" nil nil nil "5s")))

⇒ Emacs freezes for 5 seconds.

Is there a reason for this behavior? The manual claims that Emacs
yields when waiting for process output, but that only seems to be the
case for asynchronous processes. It's of course possible to simulate
synchronous processes with asynchronous processes, but the
asynchronous process API is more difficult to use.

Thanks,
Philipp