Lua - Current time in milliseconds

Question

Is there a common way to get the current time in or with milliseconds?

There is os.time(), but it only provides full seconds.

Answer 1

If you want to benchmark, you can use os.clock as shown by the doc:

local x = os.clock()
local s = 0
for i=1,100000 do s = s + i end
print(string.format("elapsed time: %.2f\n", os.clock() - x))

Answer 2

I made a suitable solution for lua on Windows. I basically did what Kevlar suggested, but with a shared library rather than a DLL. This has been tested using cygwin.

I wrote some lua compatible C code, compiled it to a shared library (.so file via gcc in cygwin), and then loaded it up in lua using package.cpath and require" ". Wrote an adapter script for convenience. Here is all of the source:

first the C code, HighResTimer.c

////////////////////////////////////////////////////////////////
//HighResTimer.c by Cody Duncan
//
//compile with:  gcc -o Timer.so -shared HighResTimer.c -llua5.1
//compiled in cygwin after installing lua (cant remember if I 
//   installed via setup or if I downloaded and compiled lua, 
//   probably the former)
////////////////////////////////////////////////////////////////
#include <windows.h>

typedef unsigned __int64 u64;
double mNanoSecondsPerCount;

#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"


int prevInit = 0;
int currInit = 0;
u64 prevTime = 0;
u64 currTime = 0;
u64 FrequencyCountPerSec;

LARGE_INTEGER frequencyTemp;
static int readHiResTimerFrequency(lua_State *L)
{
    QueryPerformanceFrequency(&frequencyTemp);
    FrequencyCountPerSec = frequencyTemp.QuadPart;
    lua_pushnumber(L, frequencyTemp.QuadPart);
    return 1;
}

LARGE_INTEGER timerTemp;
static int storeTime(lua_State *L)
{
    QueryPerformanceCounter(&timerTemp);

    if(!prevInit)
    {
        prevInit = 1;
        prevTime = timerTemp.QuadPart;
    }
    else if (!currInit)
    {
        currInit = 1;
        currTime = timerTemp.QuadPart;
    }
    else
    {
        prevTime = currTime;
        currTime = timerTemp.QuadPart;
    }

    lua_pushnumber(L, timerTemp.QuadPart);
    return 1;
}

static int getNanoElapsed(lua_State *L)
{
    double mNanoSecondsPerCount = 1000000000/(double)FrequencyCountPerSec;
    double elapsedNano = (currTime - prevTime)*mNanoSecondsPerCount;
    lua_pushnumber(L, elapsedNano);
    return 1;
}


int luaopen_HighResolutionTimer (lua_State *L) {

    static const luaL_reg mylib [] = 
    {
        {"readHiResTimerFrequency", readHiResTimerFrequency},
        {"storeTime", storeTime},
        {"getNanoElapsed", getNanoElapsed},
        {NULL, NULL}  /* sentinel */
    };

    luaL_register(L,"timer",mylib);

    return 1;
}

--

--

Now lets get it loaded up in a lua script, HighResTimer.lua .

Note: I compiled the HighResTimer.c to a shared library, Timer.so

#!/bin/lua
------------------------------------
---HighResTimer.lua by Cody Duncan
---Wraps the High Resolution Timer Functions in
---   Timer.so
------------------------------------

package.cpath = "./Timer.so"     --assuming Timer.so is in the same directory
require "HighResolutionTimer"    --load up the module
timer.readHiResTimerFrequency(); --stores the tickFrequency


--call this before code that is being measured for execution time
function start()
    timer.storeTime();
end

--call this after code that is being measured for execution time
function stop()
    timer.storeTime();
end

--once the prior two functions have been called, call this to get the 
--time elapsed between them in nanoseconds
function getNanosElapsed()
    return timer.getNanoElapsed();
end

--

--

and Finally, utilize the timer, TimerTest.lua .

#!/bin/lua
------------------------------------
---TimerTest.lua by Cody Duncan
---
---HighResTimer.lua and Timer.so must 
---   be in the same directory as 
---   this script.
------------------------------------

require './HighResTimer' 

start();
for i = 0, 3000000 do io.write("") end --do essentially nothing 3million times.
stop();

--divide nanoseconds by 1 million to get milliseconds
executionTime = getNanosElapsed()/1000000; 
io.write("execution time: ", executionTime, "ms\n");

Note: Any comments were written after pasting the source code into the post editor, so technically this is untested, but hopefully the comments didn't befuddle anything. I will be sure to come back and provide a fix if it does.

Answer 3

In standard C lua, no. You will have to settle for seconds, unless you are willing to modify the lua interpreter yourself to have os.time use the resolution you want. That may be unacceptable, however, if you are writing code for other people to run on their own and not something like a web application where you have full control of the environment.

Edit: another option is to write your own small DLL in C that extends lua with a new function that would give you the values you want, and require that dll be distributed with your code to whomever is going to be using it.

Answer 4

in openresty there is a function ngx.req.start_time.

From the docs:

Returns a floating-point number representing the timestamp (including milliseconds as the decimal part) when the current request was created.

Answer 5

I use LuaSocket to get more precision.

require "socket"
print("Milliseconds: " .. socket.gettime()*1000)

This adds a dependency of course, but works fine for personal use (in benchmarking scripts for example).

Answer 6

You can use C function gettimeofday : http://www.opengroup.org/onlinepubs/000095399/functions/gettimeofday.html

Here C library 'ul_time', function sec_usec resides in 'time' global table and returns seconds, useconds. Copy DLL to Lua folder, open it with require 'ul_time'.

http://depositfiles.com/files/3g2fx7dij