The x86 architecture supports additional memory ordering flags to mark critical sections for hardware lock elision. These must be specified in addition to an existing memory order to atomic intrinsics.
__ATOMIC_HLE_ACQUIRE
Start lock elision on a lock variable.
Memory order must be __ATOMIC_ACQUIRE
or stronger.
__ATOMIC_HLE_RELEASE
End lock elision on a lock variable.
Memory order must be __ATOMIC_RELEASE
or stronger.
When a lock acquire fails, it is required for good performance to abort
the transaction quickly. This can be done with a _mm_pause
.
#include <immintrin.h> // For _mm_pause int lockvar; /* Acquire lock with lock elision */ while (__atomic_exchange_n(&lockvar, 1, __ATOMIC_ACQUIRE|__ATOMIC_HLE_ACQUIRE)) _mm_pause(); /* Abort failed transaction */ ... /* Free lock with lock elision */ __atomic_store_n(&lockvar, 0, __ATOMIC_RELEASE|__ATOMIC_HLE_RELEASE);