util/agents/usb_hid_relay: fix concurrent access

labgrid/util/agents/usb_hid_relay.py

@@ -11,6 +11,10 @@
 - Turn digital output on and off
 """
 
+import errno
+from contextlib import contextmanager
+from time import monotonic, sleep
+
 import usb.core
 import usb.util
 
@@ -26,18 +30,35 @@ def __init__(self, **args):
             raise ValueError("Device not found")
 
         if self._dev.idVendor == 0x16C0:
-            self.set_output = self.set_output_dcttech
-            self.get_output = self.get_output_dcttech
+            self._set_output = self._set_output_dcttech
+            self._get_output = self._get_output_dcttech
         elif self._dev.idVendor == 0x5131:
-            self.set_output = self.set_output_lcus
-            self.get_output = self.get_output_lcus
+            self._set_output = self._set_output_lcus
+            self._get_output = self._get_output_lcus
         else:
             raise ValueError(f"Unknown vendor/protocol for VID {self._dev.idVendor:x}")
 
         if self._dev.is_kernel_driver_active(0):
             self._dev.detach_kernel_driver(0)
 
-    def set_output_dcttech(self, number, status):
+    @contextmanager
+    def _claimed(self):
+        timeout = monotonic() + 1.0
+        while True:
+            try:
+                usb.util.claim_interface(self._dev, 0)
+                break
+            except usb.core.USBError as e:
+                if monotonic() > timeout:
+                    raise e
+                if e.errno == errno.EBUSY:
+                    sleep(0.01)
+                else:
+                    raise e
+        yield
+        usb.util.release_interface(self._dev, 0)
+
+    def _set_output_dcttech(self, number, status):
         assert 1 <= number <= 8
         req = [0xFF if status else 0xFD, number]
         self._dev.ctrl_transfer(
@@ -48,7 +69,7 @@ def set_output_dcttech(self, number, status):
             req,  # payload
         )
 
-    def get_output_dcttech(self, number):
+    def _get_output_dcttech(self, number):
         assert 1 <= number <= 8
         resp = self._dev.ctrl_transfer(
             usb.util.CTRL_TYPE_CLASS | usb.util.CTRL_RECIPIENT_DEVICE | usb.util.ENDPOINT_IN,
@@ -59,7 +80,7 @@ def get_output_dcttech(self, number):
         )
         return bool(resp[7] & (1 << (number - 1)))
 
-    def set_output_lcus(self, number, status):
+    def _set_output_lcus(self, number, status):
         assert 1 <= number <= 8
         ep_in = self._dev[0][(0, 0)][0]
         ep_out = self._dev[0][(0, 0)][1]
@@ -68,13 +89,18 @@ def set_output_lcus(self, number, status):
         ep_out.write(req)
         ep_in.read(64)
 
-    def get_output_lcus(self, number):
+    def _get_output_lcus(self, number):
         assert 1 <= number <= 8
         # we have no information on how to read the current value
         return False
 
-    def __del__(self):
-        usb.util.release_interface(self._dev, 0)
+    def set_output(self, number, status):
+        with self._claimed():
+            self._set_output(number, status)
+
+    def get_output(self, number):
+        with self._claimed():
+            self._get_output(number)
 
 
 _relays = {}