util.async: Add next-tick configuration

Running woken runners in the next iteration of the event loop prevents
unexpected recursion, unexpected tracebacks, and is generally more
predictable.

The pattern is borrowed from util.promise, where we're now doing the same.

1 files changed, 8 insertions, 2 deletions

diff --git a/util/async.lua b/util/async.lua
index 551a5e5c..ece589cb 100644
--- a/util/async.lua
+++ b/util/async.lua
@@ -13,6 +13,9 @@ end
 
 -- Configurable functions
 local schedule_task = nil; -- schedule_task(seconds, callback)
+local next_tick = function (f)
+	f();
+end
 
 local function runner_from_thread(thread)
 	local level = 0;
@@ -62,8 +65,10 @@ local function runner_continue(thread)
 		-- If state is 'ready', it is our responsibility to update runner.state from 'waiting'.
 		-- We also have to :run(), because the queue might have further items that will not be
 		-- processed otherwise. FIXME: It's probably best to do this in a nexttick (0 timer).
-		runner.state = "ready";
-		runner:run();
+		next_tick(function ()
+			runner.state = "ready";
+			runner:run();
+		end);
 	end
 	return true;
 end
@@ -286,5 +291,6 @@ return {
 	wait_for = wait_for;
 	sleep = sleep;
 
+	set_nexttick = function(new_next_tick) next_tick = new_next_tick; end;
 	set_schedule_function = function (new_schedule_function) schedule_task = new_schedule_function; end;
 };