C# multithreading

Question

Can ICollection<T>.Count property getter be considered atomic (and, therefore, threadsafe)?

Thank you.

SLaks · Accepted Answer · 2011-03-31 13:29:24Z

7

It completely depends on the collection; ICollection<T> is just an interface.

Every collection that I know of simply returns an Int32 field in its Count getter, so it usually is atomic.
However, there is never a guarantee that the count didn't change just after you fetched the property.

answered Mar 31, 2011 at 13:29

SLaks

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Femaref · Accepted Answer · 2011-03-31 13:29:22Z

7

No, as you can only make that assumption for implementations, not an interface.

answered Mar 31, 2011 at 13:29

Femaref

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Aliostad · Accepted Answer · 2011-03-31 13:31:21Z

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Atomic would only make sense for implementation and not interface. You could have two implementations: one non-thread-safe implementation one thread safe.
List<T> is not thread safe since it does not use InterLocked.

answered Mar 31, 2011 at 13:31

Aliostad

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1 Comment

LukeH Over a year ago

How would using Interlocked make the List<T> implementation of Count thread-safe? The Count property just returns an int field, which is an atomic read. Of course, there's always the possibility that the count is already stale by the time it's returned to the caller, but that's just as likely if Interlocked was used.

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