Pause error #321
Pause error #321
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…an a thread to fix segfaults; set a max pause parameter to avoid data issues when LSL's StreamInlet's buffer is too small for the amount of data.
…uture versions of the library
| self.inlet = StreamInlet( | ||
| stream_info, | ||
| max_buflen=4 * self.max_buffer_len, # TODO: revisit this value | ||
| max_buflen=MAX_PAUSE_SECONDS + 5, |
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To help with later debugging, I would advocate adding the 5 to the max pause seconds or making it a class variable _max_buffer_paddingor similar.
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| self.inlet.open_stream(timeout=5.0) |
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or perhaps a timeout variable
bcipy/config.py
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| @@ -51,5 +51,6 @@ | |||
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| # misc configuration | |||
| WAIT_SCREEN_MESSAGE = 'Press Space to start or Esc to exit' | |||
| MAX_PAUSE_SECONDS = 360 | |||
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Is this a variable we would ever want to configure in the parameters? I can imagine it being an experiment control along with max # of pauses. This pattern works well if not.
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Good question. I think my preference is to leave it here until it comes up.
bcipy/helpers/task.py
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| elapsed_seconds = time.time() - pause_start | ||
| if elapsed_seconds >= MAX_PAUSE_SECONDS: | ||
| log.info("Pause exceeded the allowed time. Ending task.") |
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Let's add the MAX_PAUSE_SECONDS to the error message to help with debugging
I added a bug ticket for the failing MacOS builds: https://www.pivotaltracker.com/story/show/187517298 |
Overview
Ticket
https://www.pivotaltracker.com/story/show/187261791
Contributions
Discussion
Segfault issue
The LSL library has methods which must be run on the main thread of execution on linux/Mac computers. Running them in a separate thread was causing segfaults to occur. By refactoring to use multiprocessing, each of the objects that use LSL are essentially acting as the main thread, which resolves this issue. Note that we should do a timing test to confirm that the static offsets are still the same.
Pause bug
Previously we calculated the max buffer for LSL based on the maximum possible duration of an inquiry. However, we did not account for pause length. I was making the assumption that the LSL buffer would continue to accumulate data and only retain the latest (like what would happen in a ring buffer data structure). However, LSL has undefined behavior when the StreamInlet
max_buflenis exceeded. When you attempt to retrieve data after this maximum is exceeded some of the data is missing and what is returned may not even be in monotonic order. I was able to replicate this behavior without using BciPy in thelsl_buffer_test.pyscript. This script will allow us to test future versions of LSL in case we want to change our approach. Currently, the resolution is to set a fixed maximum buffer size in the configuration that accounts for the maximum amount of time we may want to pause during a session. If this is exceeded the task gracefully shuts down.Test