Added configurable wait func (#108)

Author: pylessard

doc/source/isotp/implementation.rst

@@ -252,6 +252,18 @@ The transport layer ``params`` parameter must be a dictionary with the following
 
    Sets the name of the logger from the ``logging`` module used to log info and debug information
 
+.. _param_wait_func:
+
+.. attribute:: wait_func
+   :annotation: (callable)
+
+   **default: "time.sleep"**
+
+   Defines a waiting function used to create the necessary delay between consecutive frames during a transmission, dictated by the receiver STMin. 
+   Expected signature is ``my_wait_func(delay:float) -> None``
+
+   Defaults value is the system ``sleep`` function, which can have a coarse granularity, depending on the scheduler policy. 
+
 -----
 
 .. _rate_limiter_section:
@@ -407,6 +419,9 @@ Using the approach described above, a message can be read from the link-layer an
 40us latency is far better than the latency caused by calls to ``time.sleep()`` required with v1.x. Considering that a CAN bus running at 500kbps has a message duration of about 230us,
 the latency is in the acceptable range.
 
+Finally, the delay between consecutive frames is dictated by a user-definable function passed with the :ref:`wait_func<param_wait_func>` parameter. By default, the wait function is the system ``sleep`` function.
+On machines where the ``sleep`` function has a coarse granularity and a high resolution timer is available, it is possible to pass a busy-wait function to this parameter.
+
 --------
 
 .. _backward_compatibility:

isotp/protocol.py

@@ -321,6 +321,7 @@ class Params:
         listen_mode: bool
         blocking_send: bool
         logger_name: str
+        wait_func: Callable[[float], None]
 
         def __init__(self):
             self.stmin = 0
@@ -342,6 +343,7 @@ def __init__(self):
             self.listen_mode = False
             self.blocking_send = False
             self.logger_name = TransportLayer.LOGGER_NAME
+            self.wait_func = time.sleep
 
         def set(self, key: str, val: Any, validate: bool = True) -> None:
             param_alias: Dict[str, str] = {
@@ -464,6 +466,14 @@ def validate(self) -> None:
             if not isinstance(self.logger_name, str):
                 raise ValueError('logger_name must be a string')
 
+            if not callable(self.wait_func):
+                raise ValueError('wait_func should be a callable')
+
+            try:
+                self.wait_func(0.001)
+            except Exception as e:
+                raise ValueError("Given wait_func raised an exception %s" % e)
+
     class RxState(enum.Enum):
         IDLE = 0
         WAIT_CF = 1
@@ -1557,7 +1567,7 @@ def _main_thread_fn(self) -> None:
                     delay = self.next_cf_delay()
                     assert delay is not None    # Confirmed by is_tx_transmitting_cf()
                     if delay > 0:
-                        time.sleep(delay)   # If we are transmitting CFs, no need to call rxfn, we can stream those CF with short sleep
+                        self.params.wait_func(delay)   # If we are transmitting CFs, no need to call rxfn, we can stream those CF with short sleep
                     if not self.events.stop_requested.is_set():
                         super().process(do_rx=False, do_tx=True)
                 else:

test/test_transport_layer_logic.py

@@ -1670,6 +1670,20 @@ def test_params_bad_values(self):
         params['logger_name'] = 'asd'
         self.create_layer(params)
 
+        for val in ['asd', 1.1, None]:
+            with self.assertRaises(ValueError):
+                params['wait_func'] = val
+                self.create_layer(params)
+
+        def wait_func_bad_signature():
+            pass
+
+        with self.assertRaises(ValueError):
+            params['wait_func'] = val
+            self.create_layer(params)
+
+        params['wait_func'] = time.sleep
+
 # Check the behavior of the transport layer. Sequenece of CAN frames, timings, etc.