On 04/05/2013 01:33 PM, Bjorn Lindgren wrote: > > On Fri, 5 Apr 2013, Andrew Haley wrote: > >> On 04/05/2013 12:39 PM, Bjorn Lindgren wrote: >>> I would like to know if the built-in __atomic_* function calls are always >>> garanteed to succeed? If for example multiple threads on different >>> sockets/cores call the __atomic function on a globaly shared variable at >>> same time, are the calls then queued and executed? >> >> I can't tell exactly what this question means. I think you're asking if, >> for example, an atomic_fetch-and-modify might fail to modify its target. >> The answer is no: while the cmpxchg fails it will retry. > > Well, that was what I wanted to find out, do I need error handling if the > event of a colliction (two cores exectuing CMPXCHG within the same clock > cycles), the instruction will be automaticly retried until it succeeds? Correct. > Is that true for the x86 asm implementations of __atomic_*_fetch / > __atomic_fetch_* calls too, that they are retried? Which x86 asm implementations do you mean? We're talking about GCC here, and it has builtins. > As I understand each core has it's own context and instruction > pipeline so a __atomic function call collision could > occur across cores. Indeed it could, but this is all too vague for me. Some builtins can fail, some can't. Those that can fail indicate failure with a status code. Andrew.
