E&S CVS Commit: PEAK - Change to binding.Once: if the object's dict contains 'NOT_FOUND' as the

pje at eby-sarna.com pje at eby-sarna.com
Sat Feb 22 11:22:00 EST 2003

Module Name:	PEAK
Committed By:	pje
Date:		Sat Feb 22 16:21:48 UTC 2003

Modified Files:
	PEAK/src/peak/binding: _once.c _once.pyx

Log Message:
Change to binding.Once: if the object's dict contains 'NOT_FOUND' as the
bound attribute's value, 'AttributeError' is raised upon access.  This lets
you override a bound attribute value and declare it non-existent, and it
also ensures that a circularly defined attribute will result in an error

Unfortunately, an error will also result if two threads attempt
to access and compute the bound attribute "at the same time".  But this
is a slight improvement over the situation prior to this change, where a
race condition would cause the "losing" thread to silently return
'NOT_FOUND', possibly causing the problem to lurk awhile.

The existence of this race condition is a potentially serious problem with
the use of lazy attribute bindings in class objects (which are shared
between threads), and it may be that we will need to require some type of
locking for such bindings.  :(

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