timeit

Time a snippet.

Usage

var timeit = require( '@stdlib/utils/timeit' );

timeit( code, [options,] clbk )

Times a snippet.

var code = 'var x = Math.pow( Math.random(), 3 );';
code += 'if ( x !== x ) {';
code += 'throw new Error( \'Something went wrong.\' );';
code += '}';

timeit( code, done );

function done( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
    /* e.g., returns
        {
            "iterations": 1000000,
            "repeats": 3,
            "min": [0,135734733],       // [seconds,nanoseconds]
            "elapsed": 0.135734733,     // seconds
            "rate": 7367311.062526641,  // iterations/second
            "times": [                  // raw timing results
                [0,145641393],
                [0,135734733],
                [0,140462721]
            ]
        }
    */
}

The function supports the following options:

  • before: setup code. Default: "".
  • after: cleanup code. Default: "".
  • iterations: number of iterations. If null, the number of iterations is determined by trying successive powers of 10 until the total time is at least 0.1 seconds. Default: 1e6.
  • repeats: number of repeats. Default: 3.
  • asynchronous: boolean indicating whether a snippet is asynchronous. Default: false.

To perform any setup or initialization, provide setup code.

var setup = 'var randu = require( \'@stdlib/random/base/randu\' );';
setup += 'var pow = require( \'@stdlib/math/base/special/pow\' );';

var code = 'var x = pow( randu(), 3 );';
code += 'if ( x !== x ) {';
code += 'throw new Error( \'Something went wrong.\' );';
code += '}';

var opts = {
    'before': setup
};

timeit( code, opts, done );

function done( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
}

To perform any cleanup, provide cleanup code.

var setup = 'var randu = require( \'@stdlib/random/base/randu\' );';
setup += 'var hypot = require( \'@stdlib/math/base/special/hypot\' );';

var code = 'var h = hypot( randu()*10, randu()*10 );';
code += 'if ( h < 0 || h > 200 ) {';
code += 'throw new Error( \'Something went wrong.\' );';
code += '}';

var cleanup = 'if ( h !== h ) {';
cleanup += 'throw new Error( \'Something went wrong.\' );';
cleanup += '}';

var opts = {
    'before': setup,
    'after': cleanup
};

timeit( code, opts, done );

function done( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
}

To time an asynchronous snippet, set the asynchronous option to true.

var code = 'var x = Math.pow( Math.random(), 3 );';
code += 'if ( x !== x ) {';
code += 'var err = new Error( \'Something went wrong.\' );';
code += 'next( err );';
code += '}';
code += 'process.nextTick( next );';

var opts = {
    'iterations': 1e2,
    'asynchronous': true
};

timeit( code, opts, done );

function done( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
}

If asynchronous is true, the implementation assumes that before, after, and code snippets are all asynchronous. Accordingly, these snippets should invoke a next( [error] ) callback once complete. For example, given the following snippet,

setTimeout( done, 0 );

function done( error ) {
    if ( error ) {
        return next( error );
    }
    next();
}

the implementation wraps the snippet within a function having the following signature

function wrapped( state, next ) {
    setTimeout( done, 0 );

    function done( error ) {
        if ( error ) {
            return next( error );
        }
        next();
    }
}

The state parameter is simply an empty {} which allows the before, after, and code snippets to share state.

function before( state, next ) {
    state.counter = 0;
}

function code( state, next ) {
    setTimeout( done, 0 );

    function done( error ) {
        if ( error ) {
            return next( error );
        }
        state.counter += 1;
        next();
    }
}

function after( state, next ) {
    var err;
    if ( state.counter !== state.counter ) {
        err = new Error( 'Something went wrong!' );
        return next( err );
    }
    next();
}

Notes

  • Snippets always run in strict mode.
  • Always verify results. Doing so prevents the compiler from performing dead code elimination and other optimization techniques, which would render timing results meaningless.
  • Executed code is not sandboxed and has access to the global state. You are strongly advised against timing untrusted code. To time untrusted code, do so in an isolated environment (e.g., a separate process with restricted access to both global state and the host environment).
  • Wrapping asynchronous code does add overhead, but, in most cases, the overhead should be negligible compared to the execution cost of the timed snippet.
  • Ensure that, when asynchronous is true, the main code snippet is actually asynchronous. If a snippet releases the zalgo, an error complaining about exceeding the maximum call stack size is highly likely.
  • While many benchmark frameworks calculate various statistics over raw timing results (e.g., mean and standard deviation), do not do this. Instead, consider the fastest time an approximate lower bound for how fast an environment can execute a snippet. Slower times are more likely attributable to other processes interfering with timing accuracy rather than attributable to variability in JavaScript's speed. In which case, the minimum time is most likely the only result of interest. When considering all raw timing results, apply common sense rather than statistics.

Examples

var join = require( 'path' ).join;
var readFileSync = require( '@stdlib/fs/read-file' ).sync;
var timeit = require( '@stdlib/utils/timeit' );

var before;
var code;
var opts;

before = readFileSync( join( __dirname, 'examples', 'before.txt' ), 'utf8' );
code = readFileSync( join( __dirname, 'examples', 'code.txt' ), 'utf8' );

opts = {
    'iterations': 1e6,
    'repeats': 5,
    'before': before
};

timeit( code, opts, done );

function done( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
}

CLI

Usage

Usage: timeit [options] [<code>]

Options:

  -h,    --help                Print this message.
  -V,    --version             Print the package version.
         --iterations iter     Number of iterations.
         --repeats repeats     Number of repeats. Default: 3.
         --before setup        Setup code.
         --after cleanup       Cleanup code.
         --async               Time asynchronous code.
         --format fmt          Output format: pretty, csv, json. Default: pretty.

Notes

  • When the output format is csv, the output consists of only raw timing results.
  • If not explicitly provided --iterations, the implementation tries successive powers of 10 until the total time is at least 0.1 seconds.

Examples

$ timeit "$(cat ./examples/code.txt)" --before "$(cat ./examples/before.txt)" --iterations 1000000

iterations: 1000000
repeats: 3
iterations/s: 7261975.851461222
elapsed time: 0.13770357 sec
lower bound: 0.13770357 usec/iteration

To output results as JSON,

$ timeit "$(cat ./examples/code.txt)" --before "$(cat ./examples/before.txt)" --iterations 1000000 --format json
{"iterations":1000000,"repeats":3,"min":[0,132431806],"elapsed":0.132431806,"rate":7551056.1261997735,"times":[[0,142115140],[0,132431806],[0,134808376]]}

To output results as comma-separated values (CSV),

$ timeit "$(cat ./examples/code.txt)" --before "$(cat ./examples/before.txt)" --iterations 1000000 --format csv
seconds,nanoseconds
0,139365407
0,138033545
0,135175834

To use as part of a pipeline,

$ cat ./examples/code.txt | timeit --before "$(cat ./examples/before.txt)" --iterations 1000000

iterations: 1000000
repeats: 3
iterations/s: 7433536.674260073
elapsed time: 0.134525468 sec
lower bound: 0.134525468 usec/iteration

References