The Mechanism to prevent corruption from multi-threading

[蘇思暢]

Hi everyone,

I am just wondering how APM handles the multi-threading and prevent corruption due to multi-threading.

In this page, http://dev.ardupilot.com/wiki/learning-ardupilot-threading/

It mentions the lockless data structure which is ringbuffer can prevent corruption from multi-threading.

And i read the code of UARTDriver.cpp in AP_HAL_PX4 folder, but _writebuf is just a buffer to store the data to be sent and i don't see how this works to prevent corruption from multi-threading.

Could anyone help me to solve this?

Thanks,

Best Regards

Victor Su

[Randy Mackay]

Victor,

 

      I don’t think I have the full answer for you but my guess is that only one thread ever writes to the UARTs.  So the main thread which is sending the telemetry data down to the GCSs would be writing to the telemetry UARTs but these same UARTs wouldn’t be written to by the background threads doing things like reading sensor data from the IMU.

 

    I think the only exception to this might be the console but I think corruption on the console is ok because it’s not used for communicating with anything, it’s just for logging and display in case some developer happens to be connected to it.

 

-Randy

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[蘇思暢]

Hi Randy,

Thanks for your kind answer. After i posted the question i reviewed the AP_Scheduler and i found all the accessing to the telem1 UART are in the same thread as you mentioned therefore no thread unsafety problem.

Thanks,

Best regards

Victor