fix: sync/cond and sync/pool noyields with timeout=0

	* sync/cond: caller now can "check" whether value is present in
	  condvar with cond:recv(0) and it is guarantied that this call
	  never yields
	* sync/pool: caller now can send task with {wait_timeout=0} and
	  be sure, that execution will not yield and will return proper
	  message TASK_WAS_NOT_SCHEDULED if no free workers are
	  available in the pool right now

sync/cond.lua

@@ -52,6 +52,9 @@ function cond:recv(timeout)
 	if not self.lock then
 		self.lock = fiber.cond()
 	end
+	if timeout == 0 then
+		return nil, "Timed out"
+	end
 	self.lock:wait(timeout or self.timeout)
 	self.lock = nil
 	if self.sent then

sync/pool.lua

@@ -362,11 +362,16 @@ function pool:send(func, args, opts)
 
 	self.wg:start()
 
-	while not self.terminate_cb:recv(0) and fiber.time() < deadline do
-		fiber.testcancel()
-		if self.chan:put(task, math.min(1, deadline - fiber.time())) then
-			task.published_at = fiber.time()
-			break
+	if fiber.time() <= deadline then
+		while not self.terminate_cb:recv(0) do
+			fiber.testcancel()
+			if self.chan:put(task, math.min(1, math.max(0, deadline - fiber.time()))) then
+				task.published_at = fiber.time()
+				break
+			end
+			if fiber.time() >= deadline then
+				break
+			end
 		end
 	end
 

test/01-cond.test.lua

@@ -63,4 +63,24 @@ test:deadline(function()
 
 end, 3, 'recv -> send works')
 
+test:deadline(function()
+	local cond = sync.cond()
+	local value = math.random()
+
+	test:noyield(function()
+		local no_val, err = cond:recv(0)
+		test:is(no_val, nil, 'empty cond returns no value')
+		test:is(err, 'Timed out', 'error message is timed out')
+	end)
+
+	cond:send(value)
+
+	test:noyield(function()
+		local recv, err = cond:recv(0)
+		test:is(recv, value, 'value received')
+		test:is(err, nil, 'no error returned')
+	end)
+
+end, 1, 'recv noyields when timeout=0')
+
 test:done_testing()

test/05-pool.test.lua

@@ -353,4 +353,37 @@ test:deadline(function()
 	test:is(waited, 0, "task:wait on cancelled task must return instantly")
 end, 1, "task autocancelled when wait_timeout is too low")
 
+test:deadline(function()
+	local pool = sync.pool.new('pool', 1)
+
+	local executed
+	local task, err
+
+	test:noyield(function()
+		task, err = pool:send(function() executed = true end, {},
+			{ async = true, wait_timeout = 0 })
+		test:is(err, nil, "pool with one worker raises no error on send{wait_timeout=0}")
+	end)
+
+	---@cast task sync.pool.task
+	task:wait()
+	test:is(executed, true, "task was successfully executed")
+
+	-- pool still has free slot
+	test:noyield(function ()
+		task, err = pool:send(function() fiber.yield() executed = true end, {},
+			{ async = true, wait_timeout = 0 })
+
+		test:is(err, nil, "pool with one worker raises no error on send{wait_timeout=0}")
+
+		task, err = pool:send(function() executed = true end, {},
+			{ async = true, wait_timeout = 0 })
+
+		test:is(err, pool.errors.TASK_WAS_NOT_SCHEDULED, "second task was not scheduled")
+	end)
+
+	pool:terminate()
+	pool:wait()
+end, 1, "pool:send allows put with timeout=0")
+
 test:done_testing()