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/**
* Copyright 2022 the original author or authors.
*
* 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
*
* https://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 io.micrometer.tracing;
import io.micrometer.common.lang.Nullable;
import io.micrometer.tracing.propagation.Propagator;
import java.io.Closeable;
import java.util.Map;
/**
* This API was heavily influenced by Brave. Parts of its documentation were taken
* directly from Brave.
*
* Using a tracer, you can create a root span capturing the critical path of a request.
* Child spans can be created to allocate latency relating to outgoing requests.
*
* When tracing single-threaded code, just run it inside a scoped span:
{@code
* // Start a new trace or a span within an existing trace representing an operation
* ScopedSpan span = tracer.startScopedSpan("encode");
* try {
* // The span is in "scope" so that downstream code such as loggers can see trace IDs
* return encoder.encode();
* } catch (RuntimeException | Error e) {
* span.error(e); // Unless you handle exceptions, you might not know the operation failed!
* throw e;
* } finally {
* span.end();
* }
* }
*
* When you need more features, or finer control, use the {@linkplain Span} type:
*
{@code
* // Start a new trace or a span within an existing trace representing an operation
* Span span = tracer.nextSpan().name("encode").start();
* // Put the span in "scope" so that downstream code such as loggers can see trace IDs
* try (SpanInScope ws = tracer.withSpanInScope(span)) {
* return encoder.encode();
* } catch (RuntimeException | Error e) {
* span.error(e); // Unless you handle exceptions, you might not know the operation failed!
* throw e;
* } finally {
* span.end(); // note the scope is independent of the span. Always finish a span.
* }
* }
*
* Both of the above examples report the exact same span on finish!
*
* @author OpenZipkin Brave Authors
* @author Marcin Grzejszczak
* @see Span
* @see ScopedSpan
* @see Propagator
* @since 1.0.0
*/
public interface Tracer extends BaggageManager {
/**
* A noop implementation.
*/
Tracer NOOP = new Tracer() {
@Override
public Span nextSpan() {
return Span.NOOP;
}
@Override
public Span nextSpan(Span parent) {
return Span.NOOP;
}
@Override
public SpanInScope withSpan(Span span) {
return () -> {
};
}
@Override
public ScopedSpan startScopedSpan(String name) {
return ScopedSpan.NOOP;
}
@Override
public Span.Builder spanBuilder() {
return Span.Builder.NOOP;
}
@Override
public TraceContext.Builder traceContextBuilder() {
return TraceContext.Builder.NOOP;
}
@Override
public CurrentTraceContext currentTraceContext() {
return CurrentTraceContext.NOOP;
}
@Override
public SpanCustomizer currentSpanCustomizer() {
return SpanCustomizer.NOOP;
}
@Override
public Span currentSpan() {
return Span.NOOP;
}
@Override
public Map getAllBaggage() {
return BaggageManager.NOOP.getAllBaggage();
}
@Override
public Baggage getBaggage(String name) {
return Baggage.NOOP;
}
@Override
public Baggage getBaggage(TraceContext traceContext, String name) {
return Baggage.NOOP;
}
@Override
public Baggage createBaggage(String name) {
return Baggage.NOOP;
}
@Override
public Baggage createBaggage(String name, String value) {
return Baggage.NOOP;
}
};
/**
* This creates a new span based on the current span in scope. If there's no such span
* a new trace will be created.
* @return a child span or a new trace if no span was present
*/
Span nextSpan();
/**
* This creates a new span whose parent is {@link Span}. If parent is {@code null}
* then will create act as {@link #nextSpan()}.
* @param parent parent span
* @return a child span for the given parent, {@code null} if context was empty.
*/
Span nextSpan(@Nullable Span parent);
/**
* Makes the given span the "current span" and returns an object that exits that scope
* on close. Calls to {@link #currentSpan()} and {@link #currentSpanCustomizer()} will
* affect this span until the return value is closed.
*
* The most convenient way to use this method is via the try-with-resources idiom.
*
* When tracing in-process commands, prefer {@link #startScopedSpan(String)} which
* scopes by default.
*
* Note: While downstream code might affect the span, calling this method, and calling
* close on the result have no effect on the input. For example, calling close on the
* result does not finish the span. Not only is it safe to call close, you must call
* close to end the scope, or risk leaking resources associated with the scope.
* @param span span to place into scope or null to clear the scope
* @return scope with span in it
*/
Tracer.SpanInScope withSpan(@Nullable Span span);
/**
* Returns a new child span if there's a {@link #currentSpan()} or a new trace if
* there isn't. The result is the "current span" until {@link ScopedSpan#end()} ()} is
* called.
*
* Here's an example:
{@code
* ScopedSpan span = tracer.startScopedSpan("encode");
* try {
* // The span is in "scope" so that downstream code such as loggers can see trace IDs
* return encoder.encode();
* } catch (RuntimeException | Error e) {
* span.error(e); // Unless you handle exceptions, you might not know the operation failed!
* throw e;
* } finally {
* span.end();
* }
* }
* @param name of the span in scope
* @return span in scope
*/
ScopedSpan startScopedSpan(String name);
/**
* In some cases (e.g. when dealing with
* {@link Propagator#extract(Object, Propagator.Getter)}'s we want to create a span
* that has not yet been started, yet it's heavily configurable (some options are not
* possible to be set when a span has already been started). We can achieve that by
* using a builder.
* @return a span builder
*/
Span.Builder spanBuilder();
/**
* Builder for {@link TraceContext}.
* @return a trace context builder
*/
TraceContext.Builder traceContextBuilder();
/**
* Returns the {@link CurrentTraceContext}.
* @return current trace context
*/
CurrentTraceContext currentTraceContext();
/**
* Allows to customize the current span in scope.
* @return current span customizer
*/
@Nullable
SpanCustomizer currentSpanCustomizer();
/**
* Retrieves the current span in scope or {@code null} if one is not available.
* @return current span in scope
*/
@Nullable
Span currentSpan();
/**
* Scope of a span. Needs to be closed so that resources are let go (e.g. MDC is
* cleared).
*/
interface SpanInScope extends Closeable {
@Override
void close();
}
}