Function membarrier

pub unsafe fn membarrier(cmd: i32, flags: u32, cpuid: i32) -> Result<i32, i32> 

Available on crate feature dep_nc only.

Issue memory barriers on a set of threads.

@cmd: Takes command values defined in enum membarrier_cmd. @flags: Currently needs to be 0. For future extensions.

If this system call is not implemented, -ENOSYS is returned. If the command specified does not exist, not available on the running kernel, or if the command argument is invalid, this system call returns -EINVAL. For a given command, with flags argument set to 0, this system call is guaranteed to always return the same value until reboot.

All memory accesses performed in program order from each targeted thread is guaranteed to be ordered with respect to sys_membarrier(). If we use the semantic barrier() to represent a compiler barrier forcing memory accesses to be performed in program order across the barrier, and smp_mb() to represent explicit memory barriers forcing full memory ordering across the barrier, we have the following ordering table for each pair of barrier(), sys_membarrier() and smp_mb():

The pair ordering is detailed as (O: ordered, X: not ordered):

                       barrier()   smp_mb() sys_membarrier()
       barrier()          X           X            O
       smp_mb()           X           O            O
       sys_membarrier()   O           O            O