# Module `iota::clock` APIs for accessing time from move calls, via the Clock: a unique shared object that is created at 0x6 during genesis. - [Struct `Clock`](#iota_clock_Clock) - [Constants](#@Constants_0) - [Function `timestamp_ms`](#iota_clock_timestamp_ms) - [Function `create`](#iota_clock_create) - [Function `consensus_commit_prologue`](#iota_clock_consensus_commit_prologue)

use iota::address;
use iota::hex;
use iota::object;
use iota::transfer;
use iota::tx_context;
use std::ascii;
use std::bcs;
use std::option;
use std::string;
use std::vector;

## Struct `Clock` Singleton shared object that exposes time to Move calls. This object is found at address 0x6, and can only be read (accessed via an immutable reference) by entry functions. Entry Functions that attempt to accept Clock by mutable reference or value will fail to verify, and honest validators will not sign or execute transactions that use Clock as an input parameter, unless it is passed by immutable reference.

public struct Clock has key

Fields

id: iota::object::UID
timestamp_ms: u64: The clock's timestamp, which is set automatically by a system transaction every time consensus commits a schedule, or by iota::clock::increment_for_testing during testing.

## Constants Sender is not @0x0 the system address.

const ENotSystemAddress: u64 = 0;

## Function `timestamp_ms` The clock's current timestamp as a running total of milliseconds since an arbitrary point in the past.

public fun timestamp_ms(clock: &iota::clock::Clock): u64

Implementation

public fun timestamp_ms(clock: &Clock): u64 {
    clock.timestamp_ms
}

## Function `create` Create and share the singleton Clock -- this function is called exactly once, during genesis.

fun create(ctx: &iota::tx_context::TxContext)

Implementation

fun create(ctx: &TxContext) {
    assert!(ctx.sender() == @0x0, ENotSystemAddress);
    transfer::share_object(Clock {
        id: object::clock(),
        // Initialised to zero, but set to a real timestamp by a
        // system transaction before it can be witnessed by a move
        // call.
        timestamp_ms: 0,
    })
}

## Function `consensus_commit_prologue`

fun consensus_commit_prologue(clock: &mut iota::clock::Clock, timestamp_ms: u64, ctx: &iota::tx_context::TxContext)

Implementation

fun consensus_commit_prologue(clock: &mut Clock, timestamp_ms: u64, ctx: &TxContext) {
    // Validator will make a special system call with sender set as 0x0.
    assert!(ctx.sender() == @0x0, ENotSystemAddress);
    clock.timestamp_ms = timestamp_ms
}