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Author serhiy.storchaka
Recipients mark.dickinson, serhiy.storchaka, tehybel, terry.reedy
Date 2016-08-28.04:35:22
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This is a toy example that exposes the problem, but the problem itself is not a toy problem. The key point is that calculating slice indices cause executing Python code and releases GIL. In multithread program a sequence can be changed not in toy __index__ method, but in other thread, in legitimate code. This is very hardly reproducible bug.

Variants B are not efficient. To determine the size of a sequence we should call its __len__() method. This is less efficient than using macros Py_SIZE() or PyUnicode_GET_LENGTH(). And it is not always possible to pass a sequence. In multidimensional array there is no such sequence (see for example _testbuffer.ndarray).
Date User Action Args
2016-08-28 04:35:23serhiy.storchakasetrecipients: + serhiy.storchaka, terry.reedy, mark.dickinson, tehybel
2016-08-28 04:35:23serhiy.storchakasetmessageid: <>
2016-08-28 04:35:23serhiy.storchakalinkissue27867 messages
2016-08-28 04:35:22serhiy.storchakacreate