Tracer is the interface for Span creation and interaction with the in-process context.

Users may choose to use manual or automatic Context propagation. Because of that this class offers APIs to facilitate both usages.

The automatic context propagation is done using io.opentelemetry.context.Context which is a gRPC independent implementation for in-process Context propagation mechanism which can carry scoped-values across API boundaries and between threads. Users of the library must propagate the io.opentelemetry.context.Context between different threads.

Example usage with automatic context propagation:

class MyClass {
  private static final Tracer tracer =
    openTelemetry.getTracer("instrumentation-library-name", "1.0.0");
  void doWork() {
    Span span = tracer.spanBuilder("MyClass.DoWork").startSpan();
    try (Scope ignored = span.makeCurrent()) {
      Span.current().addEvent("Starting the work.");
      doWorkInternal();
      Span.current().addEvent("Finished working.");
    } finally {
      span.end();
    }
  }
}

Example usage with manual context propagation:

class MyClass {
  private static final Tracer tracer =
    openTelemetry.getTracer("instrumentation-library-name", "1.0.0");
  void doWork(Span parent) {
    Span childSpan = tracer.spanBuilder("MyChildSpan")
        setParent(parent).startSpan();
    childSpan.addEvent("Starting the work.");
    try {
      doSomeWork(childSpan); // Manually propagate the new span down the stack.
    } finally {
      // To make sure we end the span even in case of an exception.
      childSpan.end();  // Manually end the span.
    }
  }
}