decimal threading cost?

[Robin Becker]

Does using the decimal module incur a penalty because it imports threading or do
I have to actually start a thread?

 

[Mark Dickinson]

Does using the decimal module incur a penalty because it imports threading or do
I have to actually start a thread?

There is at least one threading-related performance penalty that
doesn't involve the user actually starting a thread: any arithmetic
operation without an explicitly specified context (e.g., as invoked by
one of the standard arithmetic operators) has to make a call to
threading.local() to look up the current (thread-local) context.

I don't know offhand whether this penalty is significant for the
Python version of decimal, though it definitely *is* significant for
decimal-in-C rewrite that's in the works: it would be interesting to
do some timings against a thread-unaware version of decimal.py.

 

[Robin Becker]

There is at least one threading-related performance penalty that
doesn't involve the user actually starting a thread: any arithmetic
operation without an explicitly specified context (e.g., as invoked by
one of the standard arithmetic operators) has to make a call to
threading.local() to look up the current (thread-local) context.

I don't know offhand whether this penalty is significant for the
Python version of decimal, though it definitely *is* significant for
decimal-in-C rewrite that's in the works: it would be interesting to
do some timings against a thread-unaware version of decimal.py.

I guess I was more worried that the import might start the per thread
instruction count check even though I'm in a single thread process.