Function spinLoopHint [src]

Signals to the processor that the caller is inside a busy-wait spin-loop.

Prototype

pub inline fn spinLoopHint() void

Example

 test spinLoopHint {
    for (0..10) |_| {
        spinLoopHint();
    }
}

Source

  pub inline fn spinLoopHint() void {
    switch (builtin.target.cpu.arch) {
        // No-op instruction that can hint to save (or share with a hardware-thread)
        // pipelining/power resources
        // https://software.intel.com/content/www/us/en/develop/articles/benefitting-power-and-performance-sleep-loops.html
        .x86,
        .x86_64,
        => asm volatile ("pause"),

        // No-op instruction that serves as a hardware-thread resource yield hint.
        // https://stackoverflow.com/a/7588941
        .powerpc,
        .powerpcle,
        .powerpc64,
        .powerpc64le,
        => asm volatile ("or 27, 27, 27"),

        // `isb` appears more reliable for releasing execution resources than `yield`
        // on common aarch64 CPUs.
        // https://bugs.java.com/bugdatabase/view_bug.do?bug_id=8258604
        // https://bugs.mysql.com/bug.php?id=100664
        .aarch64,
        .aarch64_be,
        => asm volatile ("isb"),

        // `yield` was introduced in v6k but is also available on v6m.
        // https://www.keil.com/support/man/docs/armasm/armasm_dom1361289926796.htm
        .arm,
        .armeb,
        .thumb,
        .thumbeb,
        => {
            const can_yield = comptime std.Target.arm.featureSetHasAny(builtin.target.cpu.features, .{
                .has_v6k, .has_v6m,
            });
            if (can_yield) {
                asm volatile ("yield");
            }
        },

        // The 8-bit immediate specifies the amount of cycles to pause for. We can't really be too
        // opinionated here.
        .hexagon,
        => asm volatile ("pause(#1)"),

        .riscv32,
        .riscv64,
        => if (comptime std.Target.riscv.featureSetHas(builtin.target.cpu.features, .zihintpause)) {
            asm volatile ("pause");
        },

        else => {},
    }
}  