Undefined behaviour of the C-Python tests caused by lazy initialisation of stackless

Originally reported by: Anselm Kruis (Bitbucket: akruis, GitHub: akruis)

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Problem

Since change e5a2ecca2b08 Stackless initializes the stackless subsystem only if application code loads the module stackless. This causes undefined behaviour in the C-Python test suite, if the execution order of the tests gets randomized. Especially some pickling tests are sensitive, because the initialisation of Stackless enables the pickling of additional types.

I observed failures especially with 3.5-slp, but the problem exists in all 3.x branches.

Proposed Solution

I'll import stackless in the module test.support. Nearly every test-module imports this module very early. While I'm at it, I'll also unify the tests for stackless being available.

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• Bitbucket: https://bitbucket.org/stackless-dev/stackless/issue/126

Original comment by Anselm Kruis (Bitbucket: akruis, GitHub: akruis):

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Fixed in changesets:

• 3.3-slp: 3fca818f7f75
• 3.4-slp: a103f282195d
• 3.5-slp: 540d64167ee3

Not yet merged into default-slp.