Hi,
On 09/30/2009 01:53 PM, Charlie Dickens wrote:
Hi,
if I have a class A that contains a boolean variable named x, is it safe
to read and change it from different threads without using locks?
Is it guaranteed that A.x will be always True or False, and not any
other weird value that that causes it to be inconsistent (assuming I
only set it to True or False) ?
The guarantee for A.x being only True or False, is independent of whether you
use locks or not. It depends entirely on code that assigns to A.x.
I have a = A()
first thread does:
if a.x is True :
pass
2nd thread does:
a.x = False
is it safe?
what if you have code like this:
Thread 1
if a.x is True:
doSomething()
Thread 2
a.x == False
..and thread 2 executes *after* thread 1's 'if' condition but *before*
doSomething(). If that behavior is acceptable in your application, you possibly
don't even need a.x.
and what if x was a dict ? especially if the only values that are set in
the dictionary are simple: booleans, integers, floats, strings
Same logic applies.
hth,
cheers,
- steve
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