package mtime

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Monotonic clock
Time counters
Monotonic clock raw interface
Error handling
Platform support

mtime
- Mtime
  - Span
mtime.clock
- Mtime_clock

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Monotonic time clock.

Mtime_clock provides access to a system monotonic clock. This time increases monotonically and is not subject to operating system calendar time adjustments.

Only use Mtime_clock.now if you need inter-process time correlation, otherwise prefer Mtime_clock.elapsed and counters.

Consult important information about error handling and platform support.

Monotonic clock

val elapsed : unit -> Mtime.span

elapsed () is the monotonic time span elapsed since the beginning of the program.

Raises Sys_error, see error handling

val now : unit -> Mtime.t

now () is the current system-relative monotonic timestamp. Its absolute value is meaningless.

Raises Sys_error, see error handling

val period : unit -> Mtime.span option

period () is the clock's period as a monotonic time span (if available).

Time counters

type counter

The type for monotonic wall-clock time counters.

val counter : unit -> counter

counter () is a counter counting from now on.

Raises Sys_error, see error handling

val count : counter -> Mtime.span

count c is the monotonic time span elapsed since c was created.

Monotonic clock raw interface

val elapsed_ns : unit -> int64

elapsed_ns () is the unsigned 64-bit integer nanosecond monotonic time span elapsed since the beginning of the program.

Raises Sys_error, see error handling

val now_ns : unit -> int64

now_ns () is an unsigned 64-bit integer nanosecond system-relative monotonic timestamp. The absolute value is meaningless.

Raises Sys_error, see error handling

val period_ns : unit -> int64 option

period_ns () is the clock's period as an unsigned 64-bit integer nanosecond monotonic time span (if available).

Error handling

The functions elapsed, now, counter, elapsed_ns and now_ns raise Sys_error whenever they can't determine the current time or that it doesn't fit in Mtime's range. Usually this exception should only be catched at the toplevel of your program to log it and abort the program. It indicates a serious error condition in the system.

All the other functions, whose functionality is less essential, simply silently return None if they can't determine the information either because it is unavailable or because an error occured.

Platform support

Linux uses clock_gettime with CLOCK_BOOTTIME. This means that sleep time is taken into account.
Platforms with a POSIX clock use clock_gettime with CLOCK_MONOTONIC.
Darwin uses mach_continous_time. This means that sleep time is taken into account.
Windows uses Performance counters.
JavaScript uses performance.now (consult availability) which returns a double floating point value in milliseconds with resolution up to the microsecond.
JavaScript running on Node.js uses the built-in perf_hooks module, which provides an interface compatible to the performance module in browsers.