Fix send_periodic duration (#1713)

* Add test case

* Fix bug

* Improve unittest

* MR feedback

Author: Tbruno25

can/broadcastmanager.py

@@ -297,6 +297,9 @@ def _run(self) -> None:
             win32event.WaitForSingleObject(self.event.handle, 0)
 
         while not self.stopped:
+            if self.end_time is not None and time.perf_counter() >= self.end_time:
+                break
+
             # Prevent calling bus.send from multiple threads
             with self.send_lock:
                 try:
@@ -318,8 +321,7 @@ def _run(self) -> None:
 
             if not USE_WINDOWS_EVENTS:
                 msg_due_time_ns += self.period_ns
-            if self.end_time is not None and time.perf_counter() >= self.end_time:
-                break
+
             msg_index = (msg_index + 1) % len(self.messages)
 
             if USE_WINDOWS_EVENTS:

test/back2back_test.py

@@ -273,6 +273,23 @@ def test_sub_second_timestamp_resolution(self):
         self.bus2.recv(0)
         self.bus2.recv(0)
 
+    def test_send_periodic_duration(self):
+        """
+        Verify that send_periodic only transmits for the specified duration.
+
+        Regression test for #1713.
+        """
+        for params in [(0.01, 0.003), (0.1, 0.011), (1, 0.4)]:
+            duration, period = params
+            messages = []
+
+            self.bus2.send_periodic(can.Message(), period, duration)
+            while (msg := self.bus1.recv(period * 1.25)) is not None:
+                messages.append(msg)
+
+            delta_t = round(messages[-1].timestamp - messages[0].timestamp, 2)
+            assert delta_t <= duration
+
 
 @unittest.skipUnless(TEST_INTERFACE_SOCKETCAN, "skip testing of socketcan")
 class BasicTestSocketCan(Back2BackTestCase):