Python Function Execute Subprocess With Timeout

I have a project that rsync’s data from an RPM repository for a local version of this repo. The issue I was faced with was the remote mirror would sometimes stop the rsync due to overloaded network or other unforeseen issues. I wanted to use rsyncs hashing algorithm to have it start right where it left off so I wrote a function to do this. If 900 seconds was hit it usually meant there was an issue with the transfer. I also want to state here that I observed the rsync stop serving issue on many mirrors so it was not just an issue with the TCP network. I use this in production and it logs each iteration or restart. The function below will also kill the current rsync so multiple copies are not running at the same time. I also only wanted to perform 5 iterations of rsync so I use a while loop here.

Here are the individual rsync commands in the INI configuration.

Here is how I call the execute_jobs_timeout() function:

The function:

Log Snippet showing each command executing:

Python3 Subprocess and Rsync Deadlock Strace Timeout

I recently came across a tough to debug issue where I was calling a shell script from python using the subprocess module, this shell script called rsync, no matter what I would always run into a timeout situation. I fired up strace and noticed that the process was in a timeout state.

select(4, NULL, [3], [3], {60, 0}) = 0 (Timeout)

I looked at the subprocess documentation and apparently using pipes will fill the system pipe buffer.

Warning

This will deadlock when using stdout=PIPE and/or stderr=PIPE and the child process generates enough output to a pipe such that it blocks waiting for the OS pipe buffer to accept more data. Use communicate() to avoid that.

I was baffled, I finally took the approach to eliminate stderr and stdout and just check the return status of the command using run(). Here is what I finally came up with, and all was well.

Hope you find this and it helps you.