82 lines
2.4 KiB
Zig
82 lines
2.4 KiB
Zig
const std = @import("std.zig");
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const builtin = @import("builtin");
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const assert = std.debug.assert;
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const time = std.time;
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const linux = std.os.linux;
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const windows = std.os.windows;
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pub const SpinLock = struct {
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lock: u8, // TODO use a bool or enum
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pub const Held = struct {
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spinlock: *SpinLock,
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pub fn release(self: Held) void {
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// TODO: @atomicStore() https://github.com/ziglang/zig/issues/2995
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assert(@atomicRmw(u8, &self.spinlock.lock, .Xchg, 0, .Release) == 1);
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}
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};
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pub fn init() SpinLock {
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return SpinLock{ .lock = 0 };
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}
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pub fn acquire(self: *SpinLock) Held {
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var backoff = Backoff.init();
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while (@atomicRmw(u8, &self.lock, .Xchg, 1, .Acquire) != 0)
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backoff.yield();
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return Held{ .spinlock = self };
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}
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pub fn yieldCpu() void {
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switch (builtin.arch) {
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.i386, .x86_64 => asm volatile("pause" ::: "memory"),
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// .arm, .aarch64 => asm volatile("yield"),
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//
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// Causes CI to fail
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// See: https://github.com/ziglang/zig/pull/3585#issuecomment-549962765
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else => time.sleep(0),
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}
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}
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pub fn yieldThread() void {
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switch (builtin.os) {
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.linux => assert(linux.syscall0(linux.SYS_sched_yield) == 0),
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.windows => _ = windows.kernel32.SwitchToThread(),
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else => time.sleep(1 * time.microsecond),
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}
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}
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/// Provides a method to incrementally yield longer each time its called.
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pub const Backoff = struct {
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iteration: usize,
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pub fn init() @This() {
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return @This(){ .iteration = 0 };
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}
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/// Hybrid yielding from
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/// http://www.1024cores.net/home/lock-free-algorithms/tricks/spinning
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pub fn yield(self: *@This()) void {
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defer self.iteration +%= 1;
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if (self.iteration < 10) {
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yieldCpu();
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} else if (self.iteration < 20) {
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for (([30]void)(undefined)) |_| yieldCpu();
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} else if (self.iteration < 24) {
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yieldThread();
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} else if (self.iteration < 26) {
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time.sleep(1 * time.millisecond);
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} else {
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time.sleep(10 * time.millisecond);
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}
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}
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};
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};
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test "spinlock" {
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var lock = SpinLock.init();
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const held = lock.acquire();
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defer held.release();
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}
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