I need to provide synchronization to some members of a structure.
If the structure is something like this
struct SharedStruct {
int Value1;
int Value2;
}
and I have a global variable
SharedStruct obj;
I want that the write from a processor
obj.Value1 = 5; // Processor B
to be immediately visible to the other processors, so that when I test the value
if(obj.Value1 == 5) { DoSmth(); } // Processor A
else DoSmthElse();
to get the new value, not some old value from the cache.
First I though that if I use volatile when writing/reading the values, it is enough. But I read that volatile can't solve this kind o issues.
The members are guaranteed to be properly aligned on 2/4/8 byte boundaries, and writes should be atomic in this case, but I'm not sure how the cache could interfere with this.
Using memory barriers (mfence, sfence, etc.) would be enough ? Or some interlocked operations are required ?
Or maybe something like
lock mov addr, REGISTER
?
The easiest would obviously be some locking mechanism, but speed is critical and can't afford locks :(
Edit
Maybe I should clarify a bit. The value is set only once (behaves like a flag). All the other threads need just to read it. That's why I think that it may be a way to force the read of this new value without using locks.
Thanks in advance!