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time: introduce Instant (#10972)

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protty 2022-02-24 17:51:44 -06:00 committed by GitHub
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2 changed files with 161 additions and 128 deletions
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3
lib/std/c/darwin.zig
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@ -64,7 +64,8 @@ pub const fstat = if (native_arch == .aarch64) private.fstat else private.@"fsta
pub const fstatat = if (native_arch == .aarch64) private.fstatat else private.@"fstatat$INODE64";
pub extern "c" fn mach_absolute_time() u64;
pub extern "c" fn mach_timebase_info(tinfo: ?*mach_timebase_info_data) void;
pub extern "c" fn mach_continuous_time() u64;
pub extern "c" fn mach_timebase_info(tinfo: ?*mach_timebase_info_data) kern_return_t;
pub extern "c" fn malloc_size(?*const anyopaque) usize;
pub extern "c" fn posix_memalign(memptr: *?*anyopaque, alignment: usize, size: usize) c_int;

286
lib/std/time.zig
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@ -4,22 +4,23 @@ const assert = std.debug.assert;
const testing = std.testing;
const os = std.os;
const math = std.math;
const is_windows = builtin.os.tag == .windows;
pub const epoch = @import("time/epoch.zig");
/// Spurious wakeups are possible and no precision of timing is guaranteed.
pub fn sleep(nanoseconds: u64) void {
// TODO: opting out of async sleeping?
if (std.io.is_async)
if (std.io.is_async) {
return std.event.Loop.instance.?.sleep(nanoseconds);
}
if (is_windows) {
if (builtin.os.tag == .windows) {
const big_ms_from_ns = nanoseconds / ns_per_ms;
const ms = math.cast(os.windows.DWORD, big_ms_from_ns) catch math.maxInt(os.windows.DWORD);
os.windows.kernel32.Sleep(ms);
return;
}
if (builtin.os.tag == .wasi) {
const w = std.os.wasi;
const userdata: w.userdata_t = 0x0123_45678;
@ -50,6 +51,10 @@ pub fn sleep(nanoseconds: u64) void {
std.os.nanosleep(s, ns);
}
test "sleep" {
sleep(1);
}
/// Get a calendar timestamp, in seconds, relative to UTC 1970-01-01.
/// Precision of timing depends on the hardware and operating system.
/// The return value is signed because it is possible to have a date that is
@ -75,7 +80,7 @@ pub fn milliTimestamp() i64 {
/// before the epoch.
/// See `std.os.clock_gettime` for a POSIX timestamp.
pub fn nanoTimestamp() i128 {
if (is_windows) {
if (builtin.os.tag == .windows) {
// FileTime has a granularity of 100 nanoseconds and uses the NTFS/Windows epoch,
// which is 1601-01-01.
const epoch_adj = epoch.windows * (ns_per_s / 100);
@ -84,12 +89,14 @@ pub fn nanoTimestamp() i128 {
const ft64 = (@as(u64, ft.dwHighDateTime) << 32) | ft.dwLowDateTime;
return @as(i128, @bitCast(i64, ft64) + epoch_adj) * 100;
}
if (builtin.os.tag == .wasi and !builtin.link_libc) {
var ns: os.wasi.timestamp_t = undefined;
const err = os.wasi.clock_time_get(os.wasi.CLOCK.REALTIME, 1, &ns);
assert(err == .SUCCESS);
return ns;
}
var ts: os.timespec = undefined;
os.clock_gettime(os.CLOCK.REALTIME, &ts) catch |err| switch (err) {
error.UnsupportedClock, error.Unexpected => return 0, // "Precision of timing depends on hardware and OS".
@ -97,6 +104,18 @@ pub fn nanoTimestamp() i128 {
return (@as(i128, ts.tv_sec) * ns_per_s) + ts.tv_nsec;
}
test "timestamp" {
const margin = ns_per_ms * 50;
const time_0 = milliTimestamp();
sleep(ns_per_ms);
const time_1 = milliTimestamp();
const interval = time_1 - time_0;
try testing.expect(interval > 0);
// Tests should not depend on timings: skip test if outside margin.
if (!(interval < margin)) return error.SkipZigTest;
}
// Divisions of a nanosecond.
pub const ns_per_us = 1000;
pub const ns_per_ms = 1000 * ns_per_us;
@ -127,149 +146,162 @@ pub const s_per_hour = s_per_min * 60;
pub const s_per_day = s_per_hour * 24;
pub const s_per_week = s_per_day * 7;
/// A monotonic high-performance timer.
/// Timer.start() must be called to initialize the struct, which captures
/// the counter frequency on windows and darwin, records the resolution,
/// and gives the user an opportunity to check for the existnece of
/// monotonic clocks without forcing them to check for error on each read.
/// .resolution is in nanoseconds on all platforms but .start_time's meaning
/// depends on the OS. On Windows and Darwin it is a hardware counter
/// value that requires calculation to convert to a meaninful unit.
/// An Instant represents a timestamp with respect to the currently
/// executing program that ticks during suspend and can be used to
/// record elapsed time unlike `nanoTimestamp`.
///
/// It tries to sample the system's fastest and most precise timer available.
/// It also tries to be monotonic, but this is not a guarantee due to OS/hardware bugs.
/// If you need monotonic readings for elapsed time, consider `Timer` instead.
pub const Instant = struct {
timestamp: if (is_posix) os.timespec else u64,
// true if we should use clock_gettime()
const is_posix = switch (builtin.os.tag) {
.wasi => builtin.link_libc,
.windows => false,
else => true,
};
/// Queries the system for the current moment of time as an Instant.
/// This is not guaranteed to be monotonic or steadily increasing, but for most implementations it is.
/// Returns `error.Unsupported` when a suitable clock is not detected.
pub fn now() error{Unsupported}!Instant {
// QPC on windows doesn't fail on >= XP/2000 and includes time suspended.
if (builtin.os.tag == .windows) {
return Instant{ .timestamp = os.windows.QueryPerformanceCounter() };
}
// On WASI without libc, use clock_time_get directly.
if (builtin.os.tag == .wasi and !builtin.link_libc) {
var ns: os.wasi.timestamp_t = undefined;
const rc = os.wasi.clock_time_get(os.wasi.CLOCK.MONOTONIC, 1, &ns);
if (rc != .SUCCESS) return error.Unsupported;
return Instant{ .timestamp = ns };
}
// On darwin, use UPTIME_RAW instead of MONOTONIC as it ticks while suspended.
// On linux, use BOOTTIME instead of MONOTONIC as it ticks while suspended.
// On freebsd derivatives, use MONOTONIC_FAST as currently there's no precision tradeoff.
// On other posix systems, MONOTONIC is generally the fastest and ticks while suspended.
const clock_id = switch (builtin.os.tag) {
.macos, .ios, .tvos, .watchos => os.CLOCK.UPTIME_RAW,
.freebsd, .dragonfly => os.CLOCK.MONOTONIC_FAST,
.linux => os.CLOCK.BOOTTIME,
else => os.CLOCK.MONOTONIC,
};
var ts: os.timespec = undefined;
os.clock_gettime(clock_id, &ts) catch return error.Unsupported;
return Instant{ .timestamp = ts };
}
/// Quickly compares two instances between each other.
pub fn order(self: Instant, other: Instant) std.math.Order {
// windows and wasi timestamps are in u64 which is easily comparible
if (!is_posix) {
return std.math.order(self.timestamp, other.timestamp);
}
var ord = std.math.order(self.timestamp.tv_sec, other.timestamp.tv_sec);
if (ord == .eq) {
ord = std.math.order(self.timestamp.tv_nsec, other.timestamp.tv_nsec);
}
return ord;
}
/// Returns elapsed time in nanoseconds since the `earlier` Instant.
/// This assumes that the `earlier` Instant represents a moment in time before or equal to `self`.
/// This also assumes that the time that has passed between both Instants fits inside a u64 (~585 yrs).
pub fn since(self: Instant, earlier: Instant) u64 {
if (builtin.os.tag == .windows) {
// We don't need to cache QPF as it's internally just a memory read to KUSER_SHARED_DATA
// (a read-only page of info updated and mapped by the kernel to all processes):
// https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/ntddk/ns-ntddk-kuser_shared_data
// https://www.geoffchappell.com/studies/windows/km/ntoskrnl/inc/api/ntexapi_x/kuser_shared_data/index.htm
const qpc = self.timestamp - earlier.timestamp;
const qpf = os.windows.QueryPerformanceFrequency();
// 10Mhz (1 qpc tick every 100ns) is a common enough QPF value that we can optimize on it.
// https://github.com/microsoft/STL/blob/785143a0c73f030238ef618890fd4d6ae2b3a3a0/stl/inc/chrono#L694-L701
const common_qpf = 10_000_000;
if (qpf == common_qpf) {
return qpc * (ns_per_s / common_qpf);
}
// Convert to ns using fixed point.
const scale = @as(u64, std.time.ns_per_s << 32) / @intCast(u32, qpf);
const result = (@as(u96, qpc) * scale) >> 32;
return @truncate(u64, result);
}
// WASI timestamps are directly in nanoseconds
if (builtin.os.tag == .wasi and !builtin.link_libc) {
return self.timestamp - earlier.timestamp;
}
// Convert timespec diff to ns
const seconds = @intCast(u64, self.timestamp.tv_sec - earlier.timestamp.tv_sec);
const elapsed = (seconds * ns_per_s) + @intCast(u32, self.timestamp.tv_nsec);
return elapsed - @intCast(u32, earlier.timestamp.tv_nsec);
}
};
/// A monotonic, high performance timer.
///
/// Timer.start() is used to initalize the timer
/// and gives the caller an opportunity to check for the existence of a supported clock.
/// Once a supported clock is discovered,
/// it is assumed that it will be available for the duration of the Timer's use.
///
/// Monotonicity is ensured by saturating on the most previous sample.
/// This means that while timings reported are monotonic,
/// they're not guaranteed to tick at a steady rate as this is up to the underlying system.
pub const Timer = struct {
///if we used resolution's value when performing the
/// performance counter calc on windows/darwin, it would
/// be less precise
frequency: switch (builtin.os.tag) {
.windows => u64,
.macos, .ios, .tvos, .watchos => os.darwin.mach_timebase_info_data,
else => void,
},
resolution: u64,
start_time: u64,
started: Instant,
previous: Instant,
pub const Error = error{TimerUnsupported};
/// At some point we may change our minds on RAW, but for now we're
/// sticking with posix standard MONOTONIC. For more information, see:
/// https://github.com/ziglang/zig/pull/933
const monotonic_clock_id = os.CLOCK.MONOTONIC;
/// Initialize the timer structure.
/// Can only fail when running in a hostile environment that intentionally injects
/// error values into syscalls, such as using seccomp on Linux to intercept
/// `clock_gettime`.
/// Initialize the timer by querying for a supported clock.
/// Returns `error.TimerUnsupported` when such a clock is unavailable.
/// This should only fail in hostile environments such as linux seccomp misuse.
pub fn start() Error!Timer {
// This gives us an opportunity to grab the counter frequency in windows.
// On Windows: QueryPerformanceCounter will succeed on anything >= XP/2000.
// On Posix: CLOCK.MONOTONIC will only fail if the monotonic counter is not
// supported, or if the timespec pointer is out of bounds, which should be
// impossible here barring cosmic rays or other such occurrences of
// incredibly bad luck.
// On Darwin: This cannot fail, as far as I am able to tell.
if (is_windows) {
const freq = os.windows.QueryPerformanceFrequency();
return Timer{
.frequency = freq,
.resolution = @divFloor(ns_per_s, freq),
.start_time = os.windows.QueryPerformanceCounter(),
};
} else if (comptime builtin.target.isDarwin()) {
var freq: os.darwin.mach_timebase_info_data = undefined;
os.darwin.mach_timebase_info(&freq);
return Timer{
.frequency = freq,
.resolution = @divFloor(freq.numer, freq.denom),
.start_time = os.darwin.mach_absolute_time(),
};
} else {
// On Linux, seccomp can do arbitrary things to our ability to call
// syscalls, including return any errno value it wants and
// inconsistently throwing errors. Since we can't account for
// abuses of seccomp in a reasonable way, we'll assume that if
// seccomp is going to block us it will at least do so consistently
var res: os.timespec = undefined;
os.clock_getres(monotonic_clock_id, &res) catch return error.TimerUnsupported;
var ts: os.timespec = undefined;
os.clock_gettime(monotonic_clock_id, &ts) catch return error.TimerUnsupported;
return Timer{
.resolution = @intCast(u64, res.tv_sec) * ns_per_s + @intCast(u64, res.tv_nsec),
.start_time = @intCast(u64, ts.tv_sec) * ns_per_s + @intCast(u64, ts.tv_nsec),
.frequency = {},
};
}
const current = Instant.now() catch return error.TimerUnsupported;
return Timer{ .started = current, .previous = current };
}
/// Reads the timer value since start or the last reset in nanoseconds
pub fn read(self: Timer) u64 {
var clock = clockNative() - self.start_time;
return self.nativeDurationToNanos(clock);
/// Reads the timer value since start or the last reset in nanoseconds.
pub fn read(self: *Timer) u64 {
const current = self.sample();
return current.since(self.started);
}
/// Resets the timer value to 0/now.
pub fn reset(self: *Timer) void {
self.start_time = clockNative();
const current = self.sample();
self.started = current;
}
/// Returns the current value of the timer in nanoseconds, then resets it
/// Returns the current value of the timer in nanoseconds, then resets it.
pub fn lap(self: *Timer) u64 {
var now = clockNative();
var lap_time = self.nativeDurationToNanos(now - self.start_time);
self.start_time = now;
return lap_time;
const current = self.sample();
defer self.started = current;
return current.since(self.started);
}
fn clockNative() u64 {
if (is_windows) {
return os.windows.QueryPerformanceCounter();
/// Returns an Instant sampled at the callsite that is
/// guaranteed to be monotonic with respect to the timer's starting point.
fn sample(self: *Timer) Instant {
const current = Instant.now() catch unreachable;
if (current.order(self.previous) == .gt) {
self.previous = current;
}
if (comptime builtin.target.isDarwin()) {
return os.darwin.mach_absolute_time();
}
var ts: os.timespec = undefined;
os.clock_gettime(monotonic_clock_id, &ts) catch unreachable;
return @intCast(u64, ts.tv_sec) * @as(u64, ns_per_s) + @intCast(u64, ts.tv_nsec);
}
fn nativeDurationToNanos(self: Timer, duration: u64) u64 {
if (is_windows) {
return safeMulDiv(duration, ns_per_s, self.frequency);
}
if (comptime builtin.target.isDarwin()) {
return safeMulDiv(duration, self.frequency.numer, self.frequency.denom);
}
return duration;
return self.previous;
}
};
// Calculate (a * b) / c without risk of overflowing too early because of the
// multiplication.
fn safeMulDiv(a: u64, b: u64, c: u64) u64 {
const q = a / c;
const r = a % c;
// (a * b) / c == (a / c) * b + ((a % c) * b) / c
return (q * b) + (r * b) / c;
}
test "sleep" {
sleep(1);
}
test "timestamp" {
const margin = ns_per_ms * 50;
const time_0 = milliTimestamp();
sleep(ns_per_ms);
const time_1 = milliTimestamp();
const interval = time_1 - time_0;
try testing.expect(interval > 0);
// Tests should not depend on timings: skip test if outside margin.
if (!(interval < margin)) return error.SkipZigTest;
}
test "Timer" {
test "Timer + Instant" {
const margin = ns_per_ms * 150;
var timer = try Timer.start();