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Programmatic API

require('0x')(opts) => Promise -> assetPath

The opts argument is an object, with the following properties:

argv (array) – required

Pass the arguments that the spawned Node process should receive.

workingDir (string)

The base directory where profile folders will be placed.

Default: process.cwd()

pathToNodeBinary (string)

The path to any node binary executable. This will be used to run execute the script and arguments supplied in argv.

Default: Node executable according to the PATH environment variable.

name (string)

The name of the flamegraph HTML output file, without the extension.

Default: flamegraph

onPort (string)

Run a given command and then generate the flamegraph. The command as specified has access to a $PORT variable. The $PORT variable is set according to the first port that profiled process opens.

When the load-test completes, the profiled processed will be sent a SIGINT and the flamegraph will be automatically generated.

Default: ''

title (string)

Set the title to display in the flamegraph UI.

Default: argv joined by space

visualizeOnly (string)

Supply a path to a profile folder to build or rebuild visualization from original stacks.

Default: undefined

collectOnly (boolean)

Don't generate the flamegraph, only create the Profile Folder, with relevant outputs.

Default: false

collectDelay (number)

Specify a delay(ms) before collecting data.

Default: 0

mapFrames (function)

A custom mapping function that receives an array of frames and an instance of the Profiler (see stacks-to-json-stack-tree).

Takes the form (frames, profiler) => Array|false.

The frames parameter is an array of objects containing a name property.

Return false to remove the whole stack from the output, or return a modified array to change the output.

onProcessExit (function)

Called with the exit code when the observed process exits.

Default: ()=>{} (noop)

status (function)

Is called with status messages from 0x internals - useful for logging or displaying status in the console.

Default: ()=>{} (noop)

kernelTracing

Use an OS kernel tracing tool (perf on Linux or DTrace on macOS and SmartOS). This will capture native stack frames (C++ modules and Libuv I/O), but may result in missing stacks on Node 8.

See kernel-tracing.md for more information.

Default: false

outputDir (string)

Specify artifact output directory. This can be specified in template form with possible variables being {pid}, {timestamp}, {name} (based on the name option) and {outputDir}(variables must be specified without whitespace, e.g. { pid } is not supported).

Default: {pid}.0x

outputHtml (string)

Specify destination of the generated flamegraph HTML file. This can be specified in template form with possible variables being {pid}, {timestamp}, {name} (based on the name flag) and {outputDir} (variables must be specified without whitespace, e.g. { pid } is not supported). It can also be set to - to send the HTML output to STDOUT.

If either this or name is set to - then the HTML will go to STDOUT.

Default: {outputDir}/{name}.html

treeDebug (boolean)

Save the intermediate tree representation of captured trace output to a JSON file.

Default: false

kernelTracingDebug (boolean)

Show output from DTrace or perf(1) tools.

Default: false

require('0x/lib/ticks-to-tree')(ticks, opts) => Object

Build a stack tree from a list of stack samples (ticks). Useful for building custom visualizations. After a collectOnly run, the ticks data is stored in {pid}.0x/ticks.json. Read it using:

const ticks = JSON.parse(fs.readFileSync('{pid}.0x/ticks.json', 'utf8'))

opts is an object with optional properties:

  • inlined - data about inlined functions. 0x stores this in the meta.json file, which you can read like:

    const { inlined } = JSON.parse(fs.readFileSync('{pid}.0x/meta.json', 'utf8'))

  • mapFrames(frame) - See mapFrames.

  • pathToNodeBinary - Path to the Node.js executable. Defaults to process.execPath, but it's best to set this to the executable used to generate the ticks data, in case of version differences and the like.

This function returns an object with properties:

  • merged - a tree of stack frames, where each node includes both the optimized and unoptimized calls for that frame.
  • unmerged - a tree of stack frames, where each node refers to either the optimized or unoptimized calls.

Each node is an object with at least the following properties:

  • name - The function name.
  • value - The number of ticks samples this frame appeared in.
  • top - The number of ticks samples where this frame appeared at the top of the stack. (higher count = hotter function)
  • children - An array of child node objects.