lkml.org 
[lkml]   [2003]   [Jul]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Subjectatomic_set & gcc. atomicity question
Date
Hi!

Thinking about atomicity of some operations in kernel I've got the following question about atomic_XXX operations.
atomic_set and atomic_read (on i386+ and some others) are simple write to and read from memory, i.e. they are defined as:
#define atomic_set(v,i) (((v)->counter) = (i))
#define atomic_read(v) ((v)->counter)

If we call atomic_set() with constant 2nd argument it's ok - it's a simple write to var. But what if we do atomic_set(var, var1+var2)?
Probably, it can happen that compiler will do "var=var1; var+=var2", can't it? If so, atomic_read() can return intermediate value and write won't seem atomic at all. Who guarentees that compiler won't compile it this way? Optimization? gcc developers?

Kirill

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:47    [from the cache]
©2003-2011 Jasper Spaans