content: /*
   * Copyright (C) 2022 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package androidx.test.platform.tracing;
  
  import androidx.annotation.NonNull;
  import androidx.annotation.RestrictTo;
  import com.google.errorprone.annotations.MustBeClosed;
  import java.io.Closeable;
  
  /**
   * {@link Tracer} provides an API implemented by wrappers around common tracing libraries, such as
   * AndroidX Tracing. Tracer wrappers should be registered with {@link Tracing#registerTracer}.
   *
   * <p>A trace tracks the progression of various actions during testing. Each action is wrapped in a
   * "span". A span starts when the {@link #beginSpan(String)} method is called and ends when the
   * {@link Span#close()} method is called.
   *
   * <p>Traces are recursive. Within a specific span, nested spans are created by invoking {@link
   * Span#beginChildSpan(String)} and end when a corresponding {@link Span#close()} method is called.
   * Nested spans must be entirely constrained within their parent span.
   *
   * <p>The {@link Span} interface implements {@link Closeable} to encourage its use in a try-resource
   * block and ensure that the {@link Span#close()} method is always properly called. Example of
   * usage:
   *
   * <pre>
   *   class MyCustomTracingLibraryTracer implements Tracer {}
   *   Tracer tracer = new MyCustomTracingLibraryTracer();
   *   Tracing.getInstance().registerTracer(tracer);
   *   try(Span span = Tracing.getInstance().beginSpan("Some Action")) {
   *     ...action to be traced...
   *   }
   * </pre>
   *
   * @hide
   */
  @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
  public interface Tracer {
  
    /**
     * Starts a new time span to track progression of some action.
     *
     * <p>The implementation must return a {@link Span} object which the caller must use later to
     * close and end the span.
     *
     * @param name A name describing the action performed.
     * @return A new span object that the caller must invoke later to close the span.
     */
    @NonNull
    @MustBeClosed
    Span beginSpan(@NonNull String name);
  
    /**
     * Span is a helper object denoting an ongoing time span and providing a way for the caller to
     * close and end the span to record the end of the action being traced.
     *
     * <p>The Span interface implements {@link Closeable} to encourage its use in a try-resource block
     * and ensure that the {@link #close()} method is always properly called.
     */
    interface Span extends Closeable {
      /**
       * Starts a new time span nested in a parent span, to track progression of some inner action.
       *
       * <p>The implementation must return a {@link Span} object which the caller must use later to
       * close and end the span.
       *
       * <p>Multiple child spans can be created for the same parent span. It is expected that the
       * child spans do not overlap.
       *
       * @param name A name describing the inner action performed.
       * @return A new span object that the caller must invoke later to close the span.
       */
      @NonNull
      @MustBeClosed
      Span beginChildSpan(@NonNull String name);
  
      /**
       * Closes and ends this span.
       *
       * <p>Callers must not interact any further with this span.
       */
      @Override
      void close();
    }
  }
  