Circling round the distributed tracing apis

We roll back some of our usage of distributed tracing, but
in exchange get an API that works for both OpenTracing and
OpenCensus. The next step will be to push the changes back
into use within the Node, and make sure that we can see
something sensible coming out of Jaeger.

java/client/src/org/openqa/selenium/remote/tracing/BUCK

@@ -4,7 +4,7 @@ java_library(
     srcs = glob(["*.java"]),
     exported_deps = [
         # Required for the "register" API
-        "//third_party/java/opencensus:opencensus-api",
+        "//third_party/java/opencensus:opencensus",
         "//third_party/java/opentracing:opentracing-api",
     ],
     deps = [

java/client/src/org/openqa/selenium/remote/tracing/BUILD.bazel

@@ -2,14 +2,16 @@ java_library(
     name = "tracing",
     srcs = glob(["*.java"]),
     visibility = [
+        "//java/client/src/org/openqa/selenium:__subpackages__",
+        "//java/client/test/org/openqa/selenium:__subpackages__",
         "//java/server/src/org/openqa/selenium:__subpackages__",
         "//java/server/test/org/openqa/selenium:__subpackages__",
     ],
     deps = [
         "//java/client/src/org/openqa/selenium/remote",
         "//third_party/java/contrib:opentracing-tracerresolver",
         "//third_party/java/guava",
-        "//third_party/java/opencensus:opencensus-api",
+        "//third_party/java/opencensus",
         "//third_party/java/opentracing:opentracing-api",
         "//third_party/java/opentracing:opentracing-noop",
         "//third_party/java/opentracing:opentracing-util",

java/client/src/org/openqa/selenium/remote/tracing/DistributedTracer.java

@@ -17,54 +17,17 @@
 
 package org.openqa.selenium.remote.tracing;
 
-import com.google.common.collect.ImmutableMap;
-import com.google.common.collect.ImmutableSet;
-
-import org.openqa.selenium.BuildInfo;
-
-import io.opentracing.SpanContext;
 import io.opentracing.contrib.tracerresolver.TracerResolver;
 import io.opentracing.noop.NoopTracerFactory;
-import io.opentracing.propagation.Format;
-import io.opentracing.propagation.TextMap;
-import io.opentracing.propagation.TextMapExtractAdapter;
 
-import java.util.Iterator;
-import java.util.LinkedList;
-import java.util.Map;
 import java.util.Objects;
-import java.util.function.BiConsumer;
-import java.util.function.Supplier;
 
 /**
  * Represents an entry point for accessing all aspects of distributed tracing.
  */
-public class DistributedTracer {
-
-  private static volatile DistributedTracer INSTANCE = DistributedTracer.builder()
-//      .registerDetectedTracers()
-      .build();
-  private static final ThreadLocal<LinkedList<Span>> ACTIVE_SPANS =
-      ThreadLocal.withInitial(LinkedList::new);
-  private final ImmutableSet<io.opencensus.trace.Tracer> ocTracers;
-  private final ImmutableSet<io.opentracing.Tracer> otTracers;
-
-  private DistributedTracer(
-      ImmutableSet<io.opencensus.trace.Tracer> ocTracers,
-      ImmutableSet<io.opentracing.Tracer> otTracers) {
-    this.ocTracers = Objects.requireNonNull(ocTracers);
-    this.otTracers = Objects.requireNonNull(otTracers);
-  }
-
-  public static DistributedTracer getInstance() {
-    return INSTANCE;
-  }
-
-  public synchronized static void setInstance(DistributedTracer distributedTracer) {
-    INSTANCE = distributedTracer;
-  }
+public interface DistributedTracer {
 
-  public static Builder builder() {
+  static Builder builder() {
     return new Builder();
   }
 
@@ -77,143 +40,49 @@ public static Builder builder() {
    * @param parent The parent span. If this is {@code null}, then the span is
    *               assumed to be independent.
    */
-  public Span createSpan(String operation, Span parent) {
-    if (parent != null) {
-      Span child = parent.createChild(operation);
-      setActiveSpan(child);
-      return child;
-    }
-
-    ImmutableSet.Builder<Span> spans = ImmutableSet.builder();
-
-    for (io.opencensus.trace.Tracer tracer : ocTracers) {
-      spans.add(new OpenCensusSpan(this, tracer, null, "root"));
-    }
-
-    for (io.opentracing.Tracer tracer : otTracers) {
-      spans.add(new OpenTracingSpan(this, tracer, null, "root"));
-    }
-
-    Span child = new CompoundSpan(this, spans.build());
-    child.addTraceTag("selenium-version", new BuildInfo().getReleaseLabel());
-    child.addTag("selenium-client", "java");
-    setActiveSpan(child);
-    return child;
-  }
+  Span createSpan(String operation, Span parent);
 
   /**
-   * Each thread can have one currently active span. This can be accessed via
-   * this method. If there is no currently active span, then a new one will
-   * be created. Should a new span be created, it will be set as the currently
-   * active span.
+   * Get the currently active span, which may be {@code null}.
    */
-  public Span getActiveSpan() {
-    if (ACTIVE_SPANS.get().isEmpty()) {
-      return null;
-    }
-
-    return ACTIVE_SPANS.get().getLast().activate();
-  }
-
-  void setActiveSpan(Span span) {
-    ACTIVE_SPANS.get().add(span);
-  }
-
-  void remove(Span span) {
-    Objects.requireNonNull(span, "Span to remove must not be null");
-
-    ACTIVE_SPANS.get().removeIf(span::equals);
-  }
-
-  public Span extract(String operationName, Iterator<Map.Entry<String, String>> traceTags) {
-    ImmutableMap.Builder<String, String> repeatableTags = ImmutableMap.builder();
-    traceTags.forEachRemaining(item -> repeatableTags.put(item.getKey(), item.getValue()));
+  Span getActiveSpan();
 
-    ImmutableSet.Builder<Span> spans = ImmutableSet.builder();
 
-    TextMapExtractAdapter adapter = new TextMapExtractAdapter(repeatableTags.build());
-    for (io.opentracing.Tracer tracer : otTracers) {
-      SpanContext context = tracer.extract(Format.Builtin.TEXT_MAP, adapter);
+  class Builder {
 
-      spans.add(new OpenTracingSpan(this, tracer, context, operationName));
-    }
-
-    for (io.opencensus.trace.Tracer ocTracer : ocTracers) {
-      // TODO: implement for OpenCensus
-    }
-
-    return new CompoundSpan(this, spans.build()).activate();
-  }
-
-  private static class TextMapAdapter implements TextMap {
-
-    private final BiConsumer<String, String> setter;
-    private final Supplier<Iterator<Map.Entry<String, String>>> getter;
-
-    private TextMapAdapter(
-        BiConsumer<String, String> setter,
-        Supplier<Iterator<Map.Entry<String, String>>> getter) {
-
-      this.setter = setter;
-      this.getter = getter;
-    }
-
-    @Override
-    public Iterator<Map.Entry<String, String>> iterator() {
-      if (getter == null) {
-        throw new UnsupportedOperationException("iterator");
-      }
-      return getter.get();
-    }
-
-    @Override
-    public void put(String key, String value) {
-      if (setter == null) {
-        throw new UnsupportedOperationException("put");
-      }
-      if (key == null || value == null) {
-        return;
-      }
-      setter.accept(key, value);
-    }
-  }
-
-  public static class Builder {
-
-    private ImmutableSet.Builder<io.opencensus.trace.Tracer> ocTracers = ImmutableSet.builder();
-    private ImmutableSet.Builder<io.opentracing.Tracer> otTracers = ImmutableSet.builder();
+    private DistributedTracer tracer;
 
     private Builder() {
       // Only accessible through the parent class
 
-      // Make sure we have at least one tracer, but make it one that does nothing.
-      register(NoopTracerFactory.create());
+      this.tracer = new OpenTracingTracer(NoopTracerFactory.create());
     }
 
-    public Builder registerDetectedTracers() {
-      try {
-        io.opentracing.Tracer tracer = TracerResolver.resolveTracer();
-        if (tracer != null) {
-          register(tracer);
-        }
-      } catch (Exception e) {
-        // Carry on. This is fine.
-      }
+    public Builder use(io.opentracing.Tracer openTracingTracer) {
+      Objects.requireNonNull(openTracingTracer, "Tracer must be set.");
+      tracer = new OpenTracingTracer(openTracingTracer);
       return this;
     }
 
-    public Builder register(io.opentracing.Tracer openTracingTracer) {
-      otTracers.add(Objects.requireNonNull(openTracingTracer, "Tracer must be set."));
+    public Builder use(io.opencensus.trace.Tracer openCensusTracer) {
+      Objects.requireNonNull(openCensusTracer, "Tracer must be set.");
+      tracer = new OpenCensusTracer(openCensusTracer);
       return this;
     }
 
-    public Builder register(io.opencensus.trace.Tracer openCensusTracer) {
-      ocTracers.add(Objects.requireNonNull(openCensusTracer, "Tracer must be set."));
+    public Builder detect() {
+      // Checking the global tracer is futile --- it defaults to a no-op instance.
+      try {
+        this.tracer = new OpenTracingTracer(TracerResolver.resolveTracer());
+      } catch (Throwable e) {
+        // Fine. Leave the tracer as it is.
+      }
+
       return this;
     }
 
     public DistributedTracer build() {
-      return new DistributedTracer(ocTracers.build(), otTracers.build());
+      return tracer;
     }
   }
 }