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      1 // Copyright 2015 The Go Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 // Go execution tracer.
      6 // The tracer captures a wide range of execution events like goroutine
      7 // creation/blocking/unblocking, syscall enter/exit/block, GC-related events,
      8 // changes of heap size, processor start/stop, etc and writes them to an io.Writer
      9 // in a compact form. A precise nanosecond-precision timestamp and a stack
     10 // trace is captured for most events. A trace can be analyzed later with
     11 // 'go tool trace' command.
     12 package trace
     13 
     14 import (
     15 	"io"
     16 	"runtime"
     17 )
     18 
     19 // Start enables tracing for the current program.
     20 // While tracing, the trace will be buffered and written to w.
     21 // Start returns an error if tracing is already enabled.
     22 func Start(w io.Writer) error {
     23 	if err := runtime.StartTrace(); err != nil {
     24 		return err
     25 	}
     26 	go func() {
     27 		for {
     28 			data := runtime.ReadTrace()
     29 			if data == nil {
     30 				break
     31 			}
     32 			w.Write(data)
     33 		}
     34 	}()
     35 	return nil
     36 }
     37 
     38 // Stop stops the current tracing, if any.
     39 // Stop only returns after all the writes for the trace have completed.
     40 func Stop() {
     41 	runtime.StopTrace()
     42 }
     43