[Psycopg] [psycopg] #192: Decimal support not safe for use with multiple sub interpreters.

[psycopg]

#192: Decimal support not safe for use with multiple sub interpreters.
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 Reporter:  GrahamDumpleton  |        Owner:  fog          
     Type:  defect           |       Status:  new          
 Priority:  normal           |    Milestone:  PSYCOPG 2.0.6
Component:  psycopg2         |      Version:  2.0.5        
 Severity:  normal           |   Resolution:               
 Keywords:                   |  
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Comment (by piro):

 I have been testing with a per-interpreter cache into psycopg, but the
 incompatibility between the GIL and multi-interps makes me feel the
 solution not a safe one.

 I have a different solution for the adaptation failure reported in your
 discussion: register a Decimal adapter from Python using the following
 code:
 {{{
 from decimal import Decimal
 import psycopg2.extensions as ext

 # Register the Py -> PG type adapter
 ext.register_adapter(Decimal, ext.AsIs)
 }}}

 This way there will be a different adapter for each sub-interpreter and
 adaptation won't fail.

 When adapting from PG to Py you may obtain the Decimal from the wrong
 interpreter. I don't think this is a serious issue, apart that
 {{{isinstance()}}} is no more reliable.

 Psycopg initializes the decimal module only once. If this seems a problem,
 compile psycopg ''without'' decimal support using:
 {{{
 python setup.py build_ext -U HAVE_DECIMAL
 }}}
 and register a PG type for conversion to Python too:
 {{{
 # Register the PG -> Py type adapter
 ext.register_type(ext.new_type(
     (1700,), "DECIMAL",
     lambda val, cur: val and Decimal(val)))
 }}}

 you will obtain instances of the same Decimal class in all the
 interpreters anyway, because the adapters register is another module
 shared structure.

 Because mod_wsgi itself is abandoning the idea of multi-interpreters, i
 agree with Fog about the futility to have psycopg2 multi-interps-safe, or
 to consider this approach reliable at all.

-- 
Ticket URL: <http://www.initd.org/tracker/psycopg/ticket/192#comment:2>
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