Add an extra tick for explicit timeouts below resolution — to avoid infinite sleeps

docs/nuances.rst

@@ -237,7 +237,12 @@ Time arguments are converted to the internal integer form
 and back to the floating-point form when needed.
 
 The ``resolution`` (``float``) setting is the minimum supported time step.
-All time steps smaller than that are rounded to the nearest value.
+All time steps smaller than that are rounded to the nearest higher value,
+i.e., they make an extra tick of the clock. This is needed to avoid looptime
+freezing forever in a loop caused by asyncio sleeps below the resolution,
+which would otherwise (no extra tick) cause the clock moving by 0 ticks,
+thus never satisfying the asyncio's logic of reaching the target time,
+which does the math in floating point values.
 
 The default is 1 microsecond, i.e., ``0.000001`` (``1e-6``), which is good enough
 for typical unit-tests while keeping the integers smaller than 32 bits

looptime/_internal/loops.py

@@ -340,6 +340,18 @@ def __sync(
                 overtime = True
                 real_step = self.__end - self.__now
 
+        # If the original timeout is truly smaller than the resolution, add 1x clock tick.
+        # If bigger, assume it is a floating point precision error in asyncio and will be gone.
+        # But do not ceil() the time! This will expose the floating point precision errors as ticks.
+        # In particular, issue #35: asyncio.sleep(1e-7) could freeze forever,
+        # since we moved the integer clock by 0 ticks (round(1e-7/resolution)=round(0.1)=0),
+        # but asyncio.BaseLoop._run_once() slept for the remaining time in floating point math,
+        # and therefore could not reach its own target time to stop properly.
+        if not overtime:
+            if real_step is not None and timeout is not None:
+                if 0 < timeout < self.__int2time(1):
+                    real_step += 1
+
         # Normally, the real-clock step is the same as the loop-time step.
         real_timeout = self.__int2time(real_step)
 

tests/test_time_moves.py

@@ -163,3 +163,13 @@ def test_backward_time_moves_raises_and_keeps_the_time(looptime_loop):
             warnings.filterwarnings('error', category=looptime.TimeWarning)
             looptime_loop.setup_looptime(start=123)
     assert looptime_loop.time() == 456  # unmodified
+
+
+# Issue #35: freezes forever with certain sleeps below resolution.
+@pytest.mark.parametrize('sleep', [
+    0.0000001,
+    1.0000001,
+])
+def test_timeouts_below_resolution(looptime_loop, sleep):
+    looptime_loop.setup_looptime(resolution=1e-6)  # the same as in asyncio.BaseLoop._run_once()
+    looptime_loop.run_until_complete(asyncio.sleep(sleep))