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From: Reece Dunn (msclrhd_at_[hidden])
Date: 2004-09-20 06:11:57

Peter Dimov wrote:
>John Maddock wrote:
>>>I'm interested in getting something like "needs_lock" below into the
>>>normal traits, perhaps as part of boost thread. It informs you
>>>whether of not an operation on such a contiguous block needs a lock
>>>to be atomic.
>>>For example, on ia32 32 bit aligned ops are atomic, on ia64 it is 64
>>>bit. doubles on ia32 need locking to be atomic, on ia64 they don't.
>>>sizeof(void*) works generically for these two platforms as is
>>>included in the code below. A default, safety first implementation
>>>might return true always for needs lock, or perhaps, true for all
>>>sizeof's greater than a byte.
>>Is it the case that we could actually rely on this? I thought for
>>example that on IA32 operations were only atomic and thread safe when
>>the assembly is prefixed by LOCK?
>AFAIK reads and ordinary writes are atomic without LOCK. Read-modify-write
>operations need LOCK.

The Win32 API provides InterlockedXXX for atomic operations on long data
types, e.g. InterlockedIncrement. I am not sure about other OS's, but it
should be possible to define an atomic_long class:

   class atomic_long
      private: long val;
         inline atomic_long & operator++()
            InterlockedIncrement( &val );
            return( *this );
         // ...


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