[LAU] Simple, easy multithreaded circular buffer library for Linux?

[Joern Nettingsmeier]

Fons Adriaensen wrote:
> On Fri, Oct 17, 2008 at 08:06:55PM +0200, Joern Nettingsmeier wrote:
> 
>> excuse my chiming in here, i'm not really much of a c programmer... but
>> how can this
>>   -  rb->read_ptr += n1;
>>   -  rb->read_ptr &= rb->size_mask;
>>   +  rb->read_ptr = (rb->read_ptr + n1) & rb->size_mask;
>> fix anything?
>>
>> iiuc, both versions are equivalent. a context switch could happen just
>> as well after the parenthesis has been computed..!?
>> putting stuff on one line doesn't make it atomic. maybe you are now
>> getting another compiler optimization that helps to hide the bug?
> 
> The idea is that it is very unlikely that the compiler
> would store the intermediate result in rb->read_ptr,
> and so this value is updated only once.

i see. but what about the other scenario:
thread A reads read_ptr.
thread B runs and increments it.
thread A increases the old (wrong) read_ptr value by one and writes a
wrong value.

isn't that a problem here?

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