io.opencensus.trace

Class SpanBuilder

java.lang.Object

io.opencensus.trace.SpanBuilder

public abstract class SpanBuilder
extends Object

SpanBuilder is used to construct Span instances which define arbitrary scopes of code that are sampled for distributed tracing as a single atomic unit.

This is a simple example where all the work is being done within a single scope and a single thread and the Context is automatically propagated:

 class MyClass {
   private static final Tracer tracer = Tracing.getTracer();
   void doWork {
     // Create a Span as a child of the current Span.
     try (Scope ss = tracer.spanBuilder("MyChildSpan").startScopedSpan()) {
       tracer.getCurrentSpan().addAnnotation("my annotation");
       doSomeWork();  // Here the new span is in the current Context, so it can be used
                      // implicitly anywhere down the stack.
     }
   }
 }
 

There might be cases where you do not perform all the work inside one static scope and the Context is automatically propagated:

 class MyRpcServerInterceptorListener implements RpcServerInterceptor.Listener {
   private static final Tracer tracer = Tracing.getTracer();
   private Span mySpan;

   public MyRpcInterceptor() {}

   public void onRequest(String rpcName, Metadata metadata) {
     // Create a Span as a child of the remote Span.
     mySpan = tracer.spanBuilderWithRemoteParent(
         getTraceContextFromMetadata(metadata), rpcName).startSpan();
   }

   public void onExecuteHandler(ServerCallHandler serverCallHandler) {
     try (Scope ws = tracer.withSpan(mySpan)) {
       tracer.getCurrentSpan().addAnnotation("Start rpc execution.");
       serverCallHandler.run();  // Here the new span is in the current Context, so it can be
                                 // used implicitly anywhere down the stack.
     }
   }

   // Called when the RPC is canceled and guaranteed onComplete will not be called.
   public void onCancel() {
     // IMPORTANT: DO NOT forget to ended the Span here as the work is done.
     mySpan.end(EndSpanOptions.builder().setStatus(Status.CANCELLED));
   }

   // Called when the RPC is done and guaranteed onCancel will not be called.
   public void onComplete(RpcStatus rpcStatus) {
     // IMPORTANT: DO NOT forget to ended the Span here as the work is done.
     mySpan.end(EndSpanOptions.builder().setStatus(rpcStatusToCanonicalTraceStatus(status));
   }
 }
 

This is a simple example where all the work is being done within a single scope and the Context is manually propagated:

 class MyClass {
   private static final Tracer tracer = Tracing.getTracer();
   void DoWork(Span parent) {
     Span childSpan = tracer.spanBuilderWithExplicitParent("MyChildSpan", parent).startSpan();
     childSpan.addAnnotation("my annotation");
     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.
     }
   }
 }
 

If your Java version is less than Java SE 7, see startSpan() and startScopedSpan() for usage examples.

Since:

0.5

Constructor Summary

Constructors

Constructor and Description
SpanBuilder()

Method Summary

Modifier and Type	Method and Description
abstract SpanBuilder	setParentLinks(List<Span> parentLinks) Sets the List of parent links.
abstract SpanBuilder	setRecordEvents(boolean recordEvents) Sets the option Span.Options.RECORD_EVENTS for the newly created Span.
abstract SpanBuilder	setSampler(Sampler sampler) Sets the Sampler to use.
SpanBuilder	setSpanKind(Span.Kind spanKind) Sets the Span.Kind for the newly created Span.
Scope	startScopedSpan() Starts a new span and sets it as the current span.
abstract Span	startSpan() Starts a new Span.
<V> V	startSpanAndCall(Callable<V> callable) Starts a new span and calls the given Callable with the newly created Span as the current Span, and ends the Span after the Callable is called.
void	startSpanAndRun(Runnable runnable) Starts a new span and runs the given Runnable with the newly created Span as the current Span, and ends the Span after the Runnable is run.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

SpanBuilder

public SpanBuilder()

Method Detail

setSampler

public abstract SpanBuilder setSampler(Sampler sampler)

Sets the Sampler to use. If not set, the implementation will provide a default.

Parameters:

sampler - the Sampler to use when determining sampling for a Span.

Returns:

this.

Since:

0.5

setParentLinks

public abstract SpanBuilder setParentLinks(List<Span> parentLinks)

Sets the List of parent links. Links are used to link Spans in different traces. Used (for example) in batching operations, where a single batch handler processes multiple requests from different traces.

Parameters:

parentLinks - new links to be added.

Returns:

this.

Throws:

NullPointerException - if parentLinks is null.

Since:

0.5

setRecordEvents

public abstract SpanBuilder setRecordEvents(boolean recordEvents)

Sets the option Span.Options.RECORD_EVENTS for the newly created Span. If not called, the implementation will provide a default.

Parameters:

recordEvents - new value determining if this Span should have events recorded.

Returns:

this.

Since:

0.5

setSpanKind

public SpanBuilder setSpanKind(@Nullable
                               Span.Kind spanKind)

Sets the Span.Kind for the newly created Span. If not called, the implementation will provide a default.

Parameters:

spanKind - the kind of the newly created Span.

Returns:

this.

Since:

0.14

startSpan

public abstract Span startSpan()

Starts a new Span.

Users must manually call Span.end() or Span.end(EndSpanOptions) to end this Span.

Does not install the newly created Span to the current Context.

Example of usage:

 class MyClass {
   private static final Tracer tracer = Tracing.getTracer();
   void DoWork(Span parent) {
     Span childSpan = tracer.spanBuilderWithExplicitParent("MyChildSpan", parent).startSpan();
     childSpan.addAnnotation("my annotation");
     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.
     }
   }
 }
 

Returns:

the newly created Span.

Since:

0.5

startScopedSpan

@MustBeClosed
public final Scope startScopedSpan()

Starts a new span and sets it as the current span.

Enters the scope of code where the newly created Span is in the current Context, and returns an object that represents that scope. When the returned object is closed, the scope is exited, the previous Context is restored, and the newly created Span is ended using Span.end(io.opencensus.trace.EndSpanOptions).

Supports try-with-resource idiom.

Example of usage:

 class MyClass {
   private static final Tracer tracer = Tracing.getTracer();
   void doWork {
     // Create a Span as a child of the current Span.
     try (Scope ss = tracer.spanBuilder("MyChildSpan").startScopedSpan()) {
       tracer.getCurrentSpan().addAnnotation("my annotation");
       doSomeWork();  // Here the new span is in the current Context, so it can be used
                      // implicitly anywhere down the stack. Anytime in this closure the span
                      // can be accessed via tracer.getCurrentSpan().
     }
   }
 }
 

Prior to Java SE 7, you can use a finally block to ensure that a resource is closed (the Span is ended and removed from the Context) regardless of whether the try statement completes normally or abruptly.

Example of usage prior to Java SE7:

 class MyClass {
   private static Tracer tracer = Tracing.getTracer();
   void doWork {
     // Create a Span as a child of the current Span.
     Scope ss = tracer.spanBuilder("MyChildSpan").startScopedSpan();
     try {
       tracer.getCurrentSpan().addAnnotation("my annotation");
       doSomeWork();  // Here the new span is in the current Context, so it can be used
                      // implicitly anywhere down the stack. Anytime in this closure the span
                      // can be accessed via tracer.getCurrentSpan().
     } finally {
       ss.close();
     }
   }
 }
 

WARNING: The try-with-resources feature to auto-close spans as described above can sound very tempting due to its convenience, but it comes with an important and easy-to-miss trade-off: the span will be closed before any catch or finally blocks get a chance to execute. So if you need to catch any exceptions and log information about them (for example), then you do not want to use the try-with-resources shortcut because that logging will not be tagged with the span info of the span it logically falls under, and if you try to retrieve Tracer.getCurrentSpan() then you'll either get the parent span if one exists or BlankSpan if there was no parent span. This can be confusing and seem counter-intuitive, but it's the way try-with-resources works.

Returns:

an object that defines a scope where the newly created Span will be set to the current Context.

Since:

0.5

startSpanAndRun

public final void startSpanAndRun(Runnable runnable)

Starts a new span and runs the given Runnable with the newly created Span as the current Span, and ends the Span after the Runnable is run.

Any error will end up as a Status.UNKNOWN.

 tracer.spanBuilder("MyRunnableSpan").startSpanAndRun(myRunnable);
 

It is equivalent with the following code:

 Span span = tracer.spanBuilder("MyRunnableSpan").startSpan();
 Runnable newRunnable = tracer.withSpan(span, myRunnable);
 try {
   newRunnable.run();
 } finally {
   span.end();
 }
 

Parameters:

runnable - the Runnable to run in the Span.

Since:

0.11.0

startSpanAndCall

public final <V> V startSpanAndCall(Callable<V> callable)
                             throws Exception

Starts a new span and calls the given Callable with the newly created Span as the current Span, and ends the Span after the Callable is called.

Any error will end up as a Status.UNKNOWN.

 MyResult myResult = tracer.spanBuilder("MyCallableSpan").startSpanAndCall(myCallable);
 

It is equivalent with the following code:

 Span span = tracer.spanBuilder("MyCallableSpan").startSpan();
  Callable<MyResult> newCallable = tracer.withSpan(span, myCallable);
 MyResult myResult = null;
 try {
   myResult = newCallable.call();
 } finally {
   span.end();
 }
 );
 

Parameters:

callable - the Callable to run in the Span.

Throws:

Exception

Since:

0.11.0