Hi Cory,
On 13/10/09 3:47 PM, Cory Riddell wrote:
As I understand it, basically every core has it's own cache. So, if some
data is shared between multiple threads, it may be loaded into multiple
caches all at once. If one thread makes a change, the value cached by
the other core/thread is now stale. Synchronizing flushes the caches, so
any pending writes are made to the main store. The next time anybody
tries to read that value, it won't be in their cache and the data will
be read from the main store.
Just to clarify:
Yes, CPUs usually have their own caches and data can be different in the different caches.
However, this isn't what synchronization is solving. This problem (cache coherency) is
handled by the hardware.
The reason you need to do locking is because two threads (which may or may not run on
separate cores) might alter the same data in ways so that the result is no longer sane.
Cheers,
/ulrich
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