On 05/07/17 09:26, Chris Angelico wrote:
On Wed, Jul 5, 2017 at 5:56 PM, pozz <pozzu...@gmail.com> wrote:
It seems it works, but I'm not sure it is the correct way to share the
variable self.cnt. It is only written in the long thread and only read in
the main thread.
Could a single Python instruction be interrupted (in this case, self.cnt =
i)? Should I use a locking mechanism when reading/writing?
What about if the variable is more complex, for example a list or
dictionary? Even in this case, is it safe to avoid locking on a shared
variable if the operation on the variable is performed in a single Python
instruction?
You can be confident that a single assignment will happen atomically.
Even if "self.cnt = i" requires multiple instructions to perform
(which it probably doesn't), there's still going to be some moment
before the change has happened at all, and then some moment when the
change has completely happened, and you won't get a context switch in
between.
Is there a definition of what is or isn't atomic behaviour anywhere? As
an embedded C programmer I definitely wouldn't assume that a high-level
assignment (in all its ref-counting glory) would be atomic without some
hint of proof :-)
--
Rhodri James *-* Kynesim Ltd
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