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From: "\"Kirill Korotaev\" " <>
Subject: atomic_set & gcc. atomicity question
Date: Thu, 31 Jul 2003 14:00:06 +0400	[thread overview]
Message-ID: <> (raw)


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?


             reply	other threads:[~2003-07-31 10:00 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-07-31 10:00 "Kirill Korotaev"  [this message]
2003-07-31 10:46 ` atomic_set & gcc. atomicity question Raj Inguva

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