feat(trace): named tracer factory prototype 2

[mayurkale22]

Which problem is this PR solving?

• Original PR: feature(trace): adds named tracer factory #420

• This is my take (just a prototype) on named tracers for Implement Named Tracers #403.

• The factories (TracerFactory and MeterFactory) need to be a singleton object as ubiquitous points to request Tracer and Meter instances.

• I just updated the basic example to show the actual usage.

/cc @bg451

[bg451]

I take it that this would be applied to all tracers in the set and to all new tracers created afterwards?

[mayurkale22]

Yes, correct.

[codecov-io]

Codecov Report

Merging #434 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #434      +/-   ##
==========================================
- Coverage   95.88%   95.87%   -0.02%     
==========================================
  Files         108      108              
  Lines        5347     5333      -14     
  Branches      433      435       +2     
==========================================
- Hits         5127     5113      -14     
  Misses        220      220

Impacted Files	Coverage Δ
...opentelemetry-base/test/resources/resource.test.ts	100% <0%> (ø)	⬆️

[danielkhan]

Are there good reasons for the redundancy between BasicTracerFactory and NodeTracerFactory? This looks like a case where inheritance might make sense but maybe I miss something here.

[OlivierAlbertini]

LGTM

[dyladan]

The duplication between BasicTracerFactory and NodeTracerFactory seems like a good candidate for inheritance

class AbstractTracerFactory<T extends types.Tracer> implements types.TracerFactory {
  private static _singletonInstance: types.TracerFactory;
  private readonly _tracers: Map<String, T> = new Map();

  protected abstract create(): T;

  getTracer(name: string = "", version?: string): T {
    const key = name + (version != undefined ? version : "");
    if (this._tracers.has(key)) return this._tracers.get(key)!;

    const tracer = this.create();
    this._tracers.set(key, tracer);
    return tracer;
  }

  static get instance(): types.TracerFactory {
    return this._singletonInstance || (this._singletonInstance = new this());
  }
}

class NodeTracerFactory extends AbstractTracerFactory<NodeTracer> {
  protected create() {
    return new NodeTracer();
  }
}

class BasicTracerFactory extends AbstractTracerFactory<BasicTracer> {
  protected create() {
    return new BasicTracer();
  }
}

[mayurkale22]

Hey @dyladan original PR is #420, feel free to add comments on that. @bg451 has already merged changes from this to #420. Please ignore this PR, will close it soon.

[mayurkale22]

Closing this in favor of #420