Make ThreadPool.join respect the loop.min_sleep_time value.

Setting the size was already doing so. By not using the hardcoded value, this prevents a UserWarning from the libuv backend.

Also rename the attribute to  and implement it for all loops.
Add this to the ILoop interface, and test that all loop implementations correctly implement it with zope.interface.verify.verifyObject.

Fixes #1321.

CHANGES.rst

@@ -63,6 +63,10 @@
   if the socket was already in use. Now the correct socket.error
   should be raised.
 
+- Fix :meth:`gevent.threadpool.ThreadPool.join` raising a
+  `UserWarning` when using the libuv backend. Reported in
+  :issue:`1321` by ZeroNet.
+
 1.3.7 (2018-10-12)
 ==================
 

src/gevent/_interfaces.py

@@ -46,6 +46,13 @@ class ILoop(Interface):
 
     default = Attribute("Boolean indicating whether this is the default loop")
 
+    approx_timer_resolution = Attribute(
+        "Floating point number of seconds giving (approximately) the minimum "
+        "resolution of a timer (and hence the minimun value the sleep can sleep for). "
+        "On libuv, this is fixed by the library, but on libev it is just a guess "
+        "and the actual value is system dependent."
+    )
+
     def run(nowait=False, once=False):
         """
         Run the event loop.

src/gevent/libev/corecext.pyx

@@ -392,6 +392,7 @@ cdef public class loop [object PyGeventLoopObject, type PyGeventLoop_Type]:
     # the libev internal pointer to 0, and ev_is_default_loop will
     # no longer work.
     cdef bint _default
+    cdef readonly double approx_timer_resolution
 
     def __cinit__(self, object flags=None, object default=None, libev.intptr_t ptr=0):
         self.starting_timer_may_update_loop_time = 0
@@ -440,6 +441,8 @@ cdef public class loop [object PyGeventLoopObject, type PyGeventLoop_Type]:
 
     def __init__(self, object flags=None, object default=None, libev.intptr_t ptr=0):
         self._callbacks = CallbackFIFO()
+        # See libev.corecffi for this attribute.
+        self.approx_timer_resolution = 0.00001
 
     cdef _run_callbacks(self):
         cdef callback cb
@@ -745,6 +748,15 @@ cdef public class loop [object PyGeventLoopObject, type PyGeventLoop_Type]:
         # Explicitly not EV_USE_SIGNALFD
         raise AttributeError("sigfd")
 
+try:
+    from zope.interface import classImplements
+except ImportError:
+    pass
+else:
+    # XXX: This invokes the side-table lookup, we would
+    # prefer to have it stored directly on the class.
+    from gevent._interfaces import ILoop
+    classImplements(loop, ILoop)
 
 # about readonly _flags attribute:
 # bit #1 set if object owns Python reference to itself (Py_INCREF was

src/gevent/libev/corecffi.py

@@ -208,6 +208,17 @@ _events_to_str = _watchers._events_to_str # exported
 class loop(AbstractLoop):
     # pylint:disable=too-many-public-methods
 
+    # libuv parameters simply won't accept anything lower than 1ms
+    # (0.001s), but libev takes fractional seconds. In practice, on
+    # one machine, libev can sleep for very small periods of time:
+    #
+    # sleep(0.00001) -> 0.000024
+    # sleep(0.0001)  -> 0.000156
+    # sleep(0.001)   -> 0.00136 (which is comparable to libuv)
+
+    approx_timer_resolution = 0.00001
+
+
     error_handler = None
 
     _CHECK_POINTER = 'struct ev_check *'

src/gevent/libuv/loop.py

@@ -79,9 +79,10 @@ def supported_backends():
 @implementer(ILoop)
 class loop(AbstractLoop):
 
-    # XXX: Undocumented. Maybe better named 'timer_resolution'? We can't
-    # know this in general on libev
-    min_sleep_time = 0.001 # 1ms
+    # libuv parameters simply won't accept anything lower than 1ms. In
+    # practice, looping on gevent.sleep(0.001) takes about 0.00138 s
+    # (+- 0.000036s)
+    approx_timer_resolution = 0.001 # 1ms
 
     error_handler = None
 

src/gevent/tests/test__hub.py

@@ -21,6 +21,7 @@
 
 import re
 import time
+import unittest
 
 import gevent.testing as greentest
 import gevent.testing.timing
@@ -316,5 +317,16 @@ class TestPeriodicMonitoringThread(greentest.TestCase):
         self.assertIn('PeriodicMonitoringThread', data)
 
 
+class TestLoopInterface(unittest.TestCase):
+
+    def test_implemensts_ILoop(self):
+        from zope.interface import verify
+        from gevent._interfaces import ILoop
+
+        loop = get_hub().loop
+
+        verify.verifyObject(ILoop, loop)
+
+
 if __name__ == '__main__':
     greentest.main()

src/gevent/threadpool.py

@@ -114,7 +114,7 @@ class ThreadPool(GroupMappingMixin):
             self.manager.kill()
         while self._size < size:
             self._add_thread()
-        delay = getattr(self.hub.loop, 'min_sleep_time', 0.0001) # For libuv
+        delay = self.hub.loop.approx_timer_resolution
         while self._size > size:
             while self._size - size > self.task_queue.unfinished_tasks:
                 self.task_queue.put(None)
@@ -150,7 +150,7 @@ class ThreadPool(GroupMappingMixin):
 
     def join(self):
         """Waits until all outstanding tasks have been completed."""
-        delay = 0.0005
+        delay = max(0.0005, self.hub.loop.approx_timer_resolution)
         while self.task_queue.unfinished_tasks > 0:
             sleep(delay)
             delay = min(delay * 2, .05)