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const std = @import("std");
const assert = std.debug.assert;
const is_darwin = @import("builtin").target.isDarwin();
pub const Time = struct {
const Self = @This();
/// Hardware and/or software bugs can mean that the monotonic clock may regress.
/// One example (of many): https://bugzilla.redhat.com/show_bug.cgi?id=448449
/// We crash the process for safety if this ever happens, to protect against infinite loops.
/// It's better to crash and come back with a valid monotonic clock than get stuck forever.
monotonic_guard: u64 = 0,
/// A timestamp to measure elapsed time, meaningful only on the same system, not across reboots.
/// Always use a monotonic timestamp if the goal is to measure elapsed time.
/// This clock is not affected by discontinuous jumps in the system time, for example if the
/// system administrator manually changes the clock.
pub fn monotonic(self: *Self) u64 {
const m = blk: {
// Uses mach_continuous_time() instead of mach_absolute_time() as it counts while suspended.
// https://developer.apple.com/documentation/kernel/1646199-mach_continuous_time
// https://opensource.apple.com/source/Libc/Libc-1158.1.2/gen/clock_gettime.c.auto.html
if (is_darwin) {
const darwin = struct {
const mach_timebase_info_t = std.os.darwin.mach_timebase_info_data;
extern "c" fn mach_timebase_info(info: *mach_timebase_info_t) std.os.darwin.kern_return_t;
extern "c" fn mach_continuous_time() u64;
};
const now = darwin.mach_continuous_time();
var info: darwin.mach_timebase_info_t = undefined;
if (darwin.mach_timebase_info(&info) != 0) @panic("mach_timebase_info() failed");
return (now * info.numer) / info.denom;
}
// The true monotonic clock on Linux is not in fact CLOCK_MONOTONIC:
// CLOCK_MONOTONIC excludes elapsed time while the system is suspended (e.g. VM migration).
// CLOCK_BOOTTIME is the same as CLOCK_MONOTONIC but includes elapsed time during a suspend.
// For more detail and why CLOCK_MONOTONIC_RAW is even worse than CLOCK_MONOTONIC,
// see https://github.com/ziglang/zig/pull/933#discussion_r656021295.
var ts: std.os.timespec = undefined;
std.os.clock_gettime(std.os.CLOCK_BOOTTIME, &ts) catch @panic("CLOCK_BOOTTIME required");
break :blk @as(u64, @intCast(ts.tv_sec)) * std.time.ns_per_s + @as(u64, @intCast(ts.tv_nsec));
};
// "Oops!...I Did It Again"
if (m < self.monotonic_guard) @panic("a hardware/kernel bug regressed the monotonic clock");
self.monotonic_guard = m;
return m;
}
/// A timestamp to measure real (i.e. wall clock) time, meaningful across systems, and reboots.
/// This clock is affected by discontinuous jumps in the system time.
pub fn realtime(_: *Self) i64 {
// macos has supported clock_gettime() since 10.12:
// https://opensource.apple.com/source/Libc/Libc-1158.1.2/gen/clock_gettime.3.auto.html
var ts: std.os.timespec = undefined;
std.os.clock_gettime(std.os.CLOCK_REALTIME, &ts) catch unreachable;
return @as(i64, ts.tv_sec) * std.time.ns_per_s + ts.tv_nsec;
}
pub fn tick(_: *Self) void {}
};
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