Global Session

Heimdall tracks a graph of timing and domain-specific stats for performance. Stat collection and monitoring is separated from graph construction to provide control over context detail. Users can create fewer nodes to have reduced performance overhead, or create more nodes to provide more detail.

The graph obviously needs to be global. This is not a problem in the browser, but in node we may have multiple different versions of heimdalljs loaded at once. Each one will have its own Heimdall instance, but will use the same session, saved on process. This means that the session will have a heterogeneous graph of HeimdallNodes. For this reason, versions of heimdalljs that change Session, or the APIs of HeimdallNode or Cookie will use a different property to store their session (process._heimdall_session_<n>). It is quite easy for this to result in lost detail & lost stats, although it is also easy to detect this situation and issue a warning.

API

Heimdall

Creating a Heimdall instance

require('heimdalljs') to access an instance using the globally shared session.

You can create your own instance with its own session, but this is generally reommended only for testing.

var Heimdall = require('heimdalljs/heimdall');
// this will create its own session and not use the global session
var myInstance = new Heimdall();

Properties

• heimdall.current Return the leaf HeimdallNode of the currently active nodes.
• heimdall.root Return the root HeimdallNode

Functions

• heimdall.start(id, Schema) Create a new node with id id. This node becomes the active node. Its parent is the currently active node. Return this node's Cookie.
• heimdall.node(id, [Schema], callback, [context]) Create a new node, invoke callback passing in the newly created node's stats object and then stop the node.
• registerMonitor(name, Schema) register a monitor under namespace name. An error will be thrown if the reserved names own or time are used, or if a monitor with that name has already been registered for this session.
• statsFor(name) return the stats object for the monitor under namespace name.
• configFor(name) return the config object under name. Heimdall does not do anything with these config objects: it is a place for downstream consumers to share config across a heimdall session (see eg heimdalljs-logger).
• toJSON() return the json for the entire graph. This is intended to be written via JSON.stringify and then consumed by downstream apps (see eg broccoli-viz).
• visitPreOrder(callback) sugar for root.visitPreOrder(callback)
• visitPostOrder(callback) sugar for root.visitPostOrder(callback)

HeimdallNode

Identifiers

Properties

• isRoot returns true for the root node, and false for all other nodes.

Functions

• visitPreOrder(callback) visit the subtree rooted at this node with a depth-first pre-order traversal.
• visitPostOrder(callback) visit the subtree rooted at this node with a depth-first post-order traversal.
• forEachChild(callback) invoke callback for each child of this node (but not other descendants).
• remove remove this node from its parent. May only be called on an inactive, non-root node. Intended for long-running applications to free up memory after saving a subgraph via toJSONSubgraph.
• toJSON() Return the serialized representation of this ndoe.
• toJSONSubgraph() Return the serialized representation of the subtree rooted at this node.

Cookie

Functions

• stop() stop the node associated with this cookie. May only be called on the current node.
• resume() resume a stopped node. This is useful for nodes that are restarted asynchronously.

Example Usage

Simple

var heimdall = require('heimdall');

function BroccoliNodeSchema() {
  this.builds = 0;
}


heimdall.node('broccoli', function () {
  heimdall.node('node:babel', BroccoliNodeSchema, function (h) {
    h.builds++;

    heimdall.node('node:persistent-filter', BroccoliNodeSchema, function (h) {
      h.builds++;
    });

    heimdall.node('node:caching-writer', BroccoliNodeSchema, function (h) {
      h.builds++;
    });
  });
});

{
  "nodes": [{
    "id": 0,
    "name": "broccoli",
    "stats": {
      "cpu": {
        "self": 10,
      },
    },
    "children": {
      "start": [1],
      "end": [1],
    },
  }, {
    "id": 1,
    "name": "node:babel",
    "stats": {
      "builds": 1,
      "cpu": {
        "self": 20,
      },
    },
    "children": {
      "start": [2, 3],
      "end": [2, 3],
    },
  }, {
    "id": 2,
    "name": "node:persistent-filter",
    "stats": {
      "builds": 1,
      "cpu": {
        "self": 30,
      },
    },
  }, {
    "id": 3,
    "name": "node:caching-writer",
    "stats": {
      "builds": 1,
      "cpu": {
        "self": 40,
      },
    },
  }],
}

With Monitors

var heimdall = require('heimdall');
var fs = require('fs');

var origLstatSync = fs.lstatSync;
var origMkdirSync = fs.mkdirSync;

heimdall.registerMonitor('fs', function FSSchema() {
  this.lstatCount = 0;
  this.mkdirCount = 0;
});

fs.lstatSync = function () {
  heimdall.statsFor('fs').lstatCount++;
  return origLstatSync.apply(fs, arguments);
}

fs.mkdirSync = function () {
  heimdall.statsFor('fs').mkdirCount++;
  return origMkdirSync.apply(fs, arguments);
}


function BroccoliNodeSchema() {
  this.builds = 0;
}


heimdall.node('broccoli', function () {
  heimdall.node('node:babel', BroccoliNodeSchema, function (h) {
    h.builds++;

    heimdall.node('node:persistent-filter', BroccoliNodeSchema, function (h) {
      h.builds++;
      fs.mkdirSync('./tmp');
    });

    heimdall.node('node:caching-writer', BroccoliNodeSchema, function (h) {
      h.builds++;
      fs.lstatSync('./tmp');
    });
  });
});

{
  "nodes": [{
    "id": 0,
    "name": "broccoli",
    "stats": {
      "cpu": {
        "self": 10,
      },
      "fs": {
        "lstatCount": 0,
        "mkdirCount": 0,
      },
    },
    "children": {
      "start": [1],
      "end": [1],
    },
  }, {
    "id": 1,
    "name": "node:babel",
    "stats": {
      "builds": 1,
      "cpu": {
        "self": 20,
      },
      "fs": {
        "lstatCount": 0,
        "mkdirCount": 0,
      },
    },
    "children": {
      "start": [2, 3],
      "end": [2, 3],
    },
  }, {
    "id": 2,
    "name": "node:persistent-filter",
    "stats": {
      "builds": 1,
      "cpu": {
        "self": 30,
      },
      "fs": {
        "lstatCount": 0,
        "mkdirCount": 1,
      },
    },
  }, {
    "id": 3,
    "name": "node:caching-writer",
    "stats": {
      "builds": 1,
      "cpu": {
        "self": 40,
      },
      "fs": {
        "lstatCount": 1,
        "mkdirCount": 0,
      },
    },
  }],
}

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