util.async: New library to provide support around coroutine-based non-blocking functions

1 files changed, 115 insertions, 0 deletions

diff --git a/util/async.lua b/util/async.lua
new file mode 100644
index 00000000..9036a876
--- /dev/null
+++ b/util/async.lua
@@ -0,0 +1,115 @@
+local log = require "util.logger".init("util.async");
+
+local function runner_continue(thread)
+	-- ASSUMPTION: runner is in 'waiting' state (but we don't have the runner to know for sure)
+	if coroutine.status(thread) ~= "suspended" then -- This should suffice
+		return false;
+	end
+	local ok, state, runner = coroutine.resume(thread);
+	if not ok then
+		local level = 0;
+		while debug.getinfo(thread, level, "") do level = level + 1; end
+		ok, runner = debug.getlocal(thread, level-1, 1);
+		local error_handler = runner.watchers.error;
+		if error_handler then error_handler(runner, debug.traceback(thread, state)); end
+	elseif state == "ready" then
+		-- 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();
+	end
+	return true;
+end
+
+function waiter(num)
+	local thread = coroutine.running();
+	if not thread then
+		error("Not running in an async context, see http://prosody.im/doc/developers/async");
+	end
+	num = num or 1;
+	return function ()
+		coroutine.yield("wait");
+	end, function ()
+		num = num - 1;
+		if num == 0 then
+			if not runner_continue(thread) then
+				error("done() called without wait()!");
+			end
+		end
+	end;
+end
+
+local runner_mt = {};
+runner_mt.__index = runner_mt;
+
+local function runner_create_thread(func, self)
+	local thread = coroutine.create(function (self)
+		while true do
+			func(coroutine.yield("ready", self));
+		end
+	end);
+	assert(coroutine.resume(thread, self)); -- Start it up, it will return instantly to wait for the first input
+	return thread;
+end
+
+local empty_watchers = {};
+function runner(func, watchers, data)
+	return setmetatable({ func = func, thread = false, state = "ready", notified_state = "ready",
+		queue = {}, watchers = watchers or empty_watchers, data = data }
+	, runner_mt);
+end
+
+function runner_mt:run(input)
+	if input ~= nil then
+		table.insert(self.queue, input);
+	end
+	if self.state ~= "ready" then
+		return true, self.state, #self.queue;
+	end
+
+	local q, thread = self.queue, self.thread;
+	if not thread or coroutine.status(thread) == "dead" then
+		thread = runner_create_thread(self.func, self);
+		self.thread = thread;
+	end
+
+	local n, state, err = #q, self.state, nil;
+	self.state = "running";
+	while n > 0 and state == "ready" do
+		local consumed;
+		for i = 1,n do
+			local input = q[i];
+			local ok, new_state = coroutine.resume(thread, input);
+			if not ok then
+				consumed, state, err = i, "ready", debug.traceback(thread, new_state);
+				self.thread = nil;
+				break;
+			elseif state == "wait" then
+				consumed, state = i, "waiting";
+				break;
+			end
+		end
+		if not consumed then consumed = n; end
+		if q[n+1] ~= nil then
+			n = #q;
+		end
+		for i = 1, n do
+			q[i] = q[consumed+i];
+		end
+		n = #q;
+	end
+	self.state = state;
+	if state ~= self.notified_state then
+		self.notified_state = state;
+		local handler = self.watchers[state];
+		if handler then handler(self, err); end
+	end
+	return true, state, n;
+end
+
+function runner_mt:enqueue(input)
+	table.insert(self.queue, input);
+end
+
+return { waiter = waiter, runner = runner };