AlFire schrieb:
Hi,
I have a piece of software which uses threads in very massive way - like
hundreds of them generated every second.
there is also a piece of code which maintains the number of outstanding
threads, simply
counter+=1 is executed when before starting the thread and counter-=1
after it finishes.
all is very simple and by the end of the program life I expect the
counter to zero out.
however I am getting values -1, -2, 1 ,2 ,3 and quite often 0 as expected.
I guarded those statement with Lock.{acquire,release} and now it always
returns 0.
But I still can not believe that +=1 is not a thread safe operation.
don't confuse augmented assignment with incrementation as it is offered
by C (if your data-type actually fits into a single addressable memory
spot, that is)
python's += works like this
a += b <=> a = a.__iadd__(b)
Thus you actually get a situation where the expression on the right is
evaluated but not yet assigned - and then another thread can take over
control, computing with the old value of a.
Diez
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