when subprocess throws error, try to get system message; make sure error code prints correctly

[mitzimorris]

Summary:

When a subprocess fails, the error code is an unsigned int (?) but is printed as a signed int - error codes > 127 become negative, e.g. '-11'. add mode logic to get system error message for the error code and cast return code to prevent manglinag.

Description:

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Additional Information:

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Current Version:

[mitzimorris]

still how to interpret return codes above 127. e.g., running CmdStan via bash shell with segfault terminated by signal -6 is reported as return code 134 - 128 + 6 or ???
in any case, PR #358 will improve error reporting.

[mitzimorris]

maybe this is the answer to some problems: https://stackoverflow.com/a/13789263

[ahartikainen]

np.uint8(np.int8(-6)) == 250 ?

[mitzimorris]

hi @ahartikainen - context?

https://docs.python.org/3/library/subprocess.html#subprocess.CompletedProcess.returncode
question: on which architectures are posix threads used? or never?

[ahartikainen]

Hah, nevermind. So '-11' -> 11 on posix systems?

[mitzimorris]

so it would seem.