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diff --git a/src/runtime/trace/trace.go b/src/runtime/trace/trace.go
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+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package trace contains facilities for programs to generate traces
+// for the Go execution tracer.
+//
+// # Tracing runtime activities
+//
+// The execution trace captures a wide range of execution events such as
+// goroutine creation/blocking/unblocking, syscall enter/exit/block,
+// GC-related events, changes of heap size, processor start/stop, etc.
+// When CPU profiling is active, the execution tracer makes an effort to
+// include those samples as well.
+// A precise nanosecond-precision timestamp and a stack trace is
+// captured for most events. The generated trace can be interpreted
+// using `go tool trace`.
+//
+// Support for tracing tests and benchmarks built with the standard
+// testing package is built into `go test`. For example, the following
+// command runs the test in the current directory and writes the trace
+// file (trace.out).
+//
+//	go test -trace=trace.out
+//
+// This runtime/trace package provides APIs to add equivalent tracing
+// support to a standalone program. See the Example that demonstrates
+// how to use this API to enable tracing.
+//
+// There is also a standard HTTP interface to trace data. Adding the
+// following line will install a handler under the /debug/pprof/trace URL
+// to download a live trace:
+//
+//	import _ "net/http/pprof"
+//
+// See the [net/http/pprof] package for more details about all of the
+// debug endpoints installed by this import.
+//
+// # User annotation
+//
+// Package trace provides user annotation APIs that can be used to
+// log interesting events during execution.
+//
+// There are three types of user annotations: log messages, regions,
+// and tasks.
+//
+// [Log] emits a timestamped message to the execution trace along with
+// additional information such as the category of the message and
+// which goroutine called [Log]. The execution tracer provides UIs to filter
+// and group goroutines using the log category and the message supplied
+// in [Log].
+//
+// A region is for logging a time interval during a goroutine's execution.
+// By definition, a region starts and ends in the same goroutine.
+// Regions can be nested to represent subintervals.
+// For example, the following code records four regions in the execution
+// trace to trace the durations of sequential steps in a cappuccino making
+// operation.
+//
+//	trace.WithRegion(ctx, "makeCappuccino", func() {
+//
+//	   // orderID allows to identify a specific order
+//	   // among many cappuccino order region records.
+//	   trace.Log(ctx, "orderID", orderID)
+//
+//	   trace.WithRegion(ctx, "steamMilk", steamMilk)
+//	   trace.WithRegion(ctx, "extractCoffee", extractCoffee)
+//	   trace.WithRegion(ctx, "mixMilkCoffee", mixMilkCoffee)
+//	})
+//
+// A task is a higher-level component that aids tracing of logical
+// operations such as an RPC request, an HTTP request, or an
+// interesting local operation which may require multiple goroutines
+// working together. Since tasks can involve multiple goroutines,
+// they are tracked via a [context.Context] object. [NewTask] creates
+// a new task and embeds it in the returned [context.Context] object.
+// Log messages and regions are attached to the task, if any, in the
+// Context passed to [Log] and [WithRegion].
+//
+// For example, assume that we decided to froth milk, extract coffee,
+// and mix milk and coffee in separate goroutines. With a task,
+// the trace tool can identify the goroutines involved in a specific
+// cappuccino order.
+//
+//	ctx, task := trace.NewTask(ctx, "makeCappuccino")
+//	trace.Log(ctx, "orderID", orderID)
+//
+//	milk := make(chan bool)
+//	espresso := make(chan bool)
+//
+//	go func() {
+//	        trace.WithRegion(ctx, "steamMilk", steamMilk)
+//	        milk <- true
+//	}()
+//	go func() {
+//	        trace.WithRegion(ctx, "extractCoffee", extractCoffee)
+//	        espresso <- true
+//	}()
+//	go func() {
+//	        defer task.End() // When assemble is done, the order is complete.
+//	        <-espresso
+//	        <-milk
+//	        trace.WithRegion(ctx, "mixMilkCoffee", mixMilkCoffee)
+//	}()
+//
+// The trace tool computes the latency of a task by measuring the
+// time between the task creation and the task end and provides
+// latency distributions for each task type found in the trace.
+package trace
+
+import (
+	"io"
+	"runtime"
+	"sync"
+	"sync/atomic"
+)
+
+// Start enables tracing for the current program.
+// While tracing, the trace will be buffered and written to w.
+// Start returns an error if tracing is already enabled.
+func Start(w io.Writer) error {
+	tracing.Lock()
+	defer tracing.Unlock()
+
+	if err := runtime.StartTrace(); err != nil {
+		return err
+	}
+	go func() {
+		for {
+			data := runtime.ReadTrace()
+			if data == nil {
+				break
+			}
+			w.Write(data)
+		}
+	}()
+	tracing.enabled.Store(true)
+	return nil
+}
+
+// Stop stops the current tracing, if any.
+// Stop only returns after all the writes for the trace have completed.
+func Stop() {
+	tracing.Lock()
+	defer tracing.Unlock()
+	tracing.enabled.Store(false)
+
+	runtime.StopTrace()
+}
+
+var tracing struct {
+	sync.Mutex // gate mutators (Start, Stop)
+	enabled    atomic.Bool
+}