search for: get_value_when_ready

struct { volatile int flag; int value; } s; int get_value_when_ready() { while (s.flag) ; __sync_synchronize(); return s.value; } This is "valid" legacy code on some processors, yet it's not valid to replace __sync_synchronize with an atomic_thread_fence because, in theory, LLVM could hoist the load of s.value. In practice it currently doesn'...

2013/7/31 JF Bastien <jfb at google.com>: > Hi, > > TL;DR: should we add a new memory ordering to fences? > > > ``fence seq_cst`` is currently use to represent two things: > - GCC-style builtin ``__sync_synchronize()`` [0][1]. > - C11/C++11's sequentially-consistent thread fence > ``std::atomic_thread_fence(std::memory_order_seq_cst)`` [2]. > > As far

...mory model would apply, and I don't think the instructions emitted would change at all on the platforms I'm familiar with. Jeffrey On Wed, Jul 31, 2013 at 4:15 PM, JF Bastien <jfb at google.com> wrote: > struct { > volatile int flag; > int value; > } s; > > int get_value_when_ready() { > while (s.flag) ; > __sync_synchronize(); > return s.value; > } > > This is "valid" legacy code on some processors, yet it's not valid to > replace __sync_synchronize with an atomic_thread_fence because, in > theory, LLVM could hoist the load of s.va...

Hi, TL;DR: should we add a new memory ordering to fences? ``fence seq_cst`` is currently use to represent two things: - GCC-style builtin ``__sync_synchronize()`` [0][1]. - C11/C++11's sequentially-consistent thread fence ``std::atomic_thread_fence(std::memory_order_seq_cst)`` [2]. As far as I understand: - The former orders all memory and emits an actual fence instruction. - The