InterLocked and align

[Ajay Vijay]

The function will not perform any automatic alignment for non-aligned data for you.

Non aligned 'int':

#pragma pack(1) // 1 byte alignment
struct Test
{
   char a;
   int b;
};

Here the variable 'b' at (base+1) offset to the Test struct. If you do not specify #pragma pack directive, compiler will pack the data as per project settings (either 4-byte, or 8-byte is standard). In that case 'b' would be aligned in 4-byte boundary.
Now assume you have a function, that takes int* or int& as an argument:

void f(int*);
...
Test t;
t.b=100;
f( &t.b );

In function 'f' you might access/modify the passed variable. The variable (pointer/reference) is NOT properly-aligned and the x86 CPU will align it for you in 4-byte boundary. 64-bit processor will NOT align!

If you pass 't.b' variable to InterlockedXX function, the passed variable (pointer) is NOT aligned properly, and thus the unpredictable behaviour!