service() fails to run inside later::with_temp_loop()

[RLesur]

Originally posted in rstudio/pagedown#150

This issue is related to later >= 1.0.0 which introduces private event loops.

The first observation is that httpuv uses only the global event loop even if startServer() is called inside later::with_temp_loop().

The problem is that service() does not execute the callbacks registered in the global loop when called inside later::with_temp_loop().
This comes from the fact that later::run_now() executes the callbacks registered in the current loop.

httpuv/R/httpuv.R

Lines 588 to 615 in 57e1d71

	service <- function(timeoutMs = ifelse(interactive(), 100, 1000)) {
	# In all cases, call `run_now` with `all = FALSE` so that if there is a lot of
	# incoming traffic (relative to the time it takes to process it) we give the
	# owning event loop opportunities to do housekeeping in between httpuv related
	# callbacks.
	if (is.na(timeoutMs)) {
	# NA means to run non-blocking
	run_now(0, all = FALSE)
	} else if (timeoutMs == 0 || timeoutMs == Inf) {
	.globals$paused <- FALSE
	# In interactive sessions, wait for a max of 0.1 seconds for better
	# responsiveness when the user sends an interrupt (like Esc in RStudio.)
	check_time <- if (interactive()) 0.1 else Inf
	while (!.globals$paused) {
	run_now(check_time, all = FALSE)
	}
	} else {
	# No need to check for .globals$paused because if run_now() executes
	# anything, it will return immediately.
	run_now(timeoutMs / 1000, all = FALSE)
	}
	# Some code expects service() to return TRUE (#123)
	TRUE
	}

For now, the workaround is to use later::with_loop(later::global_loop(), httpuv::service()) instead of httpuv::service().