driver: SigrokDriver avoid deadlock when sigrok-cli process failed

The driver expected that the sigrok-cli is successful and starts
capturing in continuous mode. When the call is unsuccessful,
the driver then waited for the creation of the capture file forever.

Fixed by checking if the sigrok-cli process terminated prematurely
while waiting for the existence of the capture file.

Signed-off-by: Felix Zwettler <Felix.Zwettler@duagon.com>

Author: flxzt

labgrid/driver/sigrokdriver.py

@@ -149,6 +149,16 @@ def capture(self, filename, samplerate="200k"):
         args = self.sigrok.command_prefix + ['test', '-e', filename]
 
         while subprocess.call(args):
+            # in case the sigrok-cli call fails, this would wait forever.
+            # to avoid this, we also check the spawned sigrok process
+            if self._process.poll() is not None:
+                ret = self._process.returncode
+                if ret != 0:
+                    stdout, stderr = self._process.communicate()
+                    self.logger.debug("sigrok-cli call terminated prematurely with non-zero return-code")
+                    self.logger.debug("stdout: %s", stdout)
+                    self.logger.debug("stderr: %s", stderr)
+                    raise ExecutionError(f"sigrok-cli call terminated prematurely with return-code '{ret}'.")
             sleep(0.1)
 
         self._running = True