traceback_ancestors.go

     1  // Copyright 2018 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  package main
     6  
     7  import (
     8  	"bytes"
     9  	"fmt"
    10  	"runtime"
    11  	"strings"
    12  )
    13  
    14  func init() {
    15  	register("TracebackAncestors", TracebackAncestors)
    16  }
    17  
    18  const numGoroutines = 3
    19  const numFrames = 2
    20  
    21  func TracebackAncestors() {
    22  	w := make(chan struct{})
    23  	recurseThenCallGo(w, numGoroutines, numFrames, true)
    24  	<-w
    25  	printStack()
    26  	close(w)
    27  }
    28  
    29  var ignoreGoroutines = make(map[string]bool)
    30  
    31  func printStack() {
    32  	buf := make([]byte, 1024)
    33  	for {
    34  		n := runtime.Stack(buf, true)
    35  		if n < len(buf) {
    36  			all := string(buf[:n])
    37  			var saved string
    38  
    39  			// Delete any ignored goroutines, if present.
    40  			for all != "" {
    41  				var g string
    42  				g, all, _ = strings.Cut(all, "\n\n")
    43  
    44  				if strings.HasPrefix(g, "goroutine ") {
    45  					id, _, _ := strings.Cut(strings.TrimPrefix(g, "goroutine "), " ")
    46  					if ignoreGoroutines[id] {
    47  						continue
    48  					}
    49  				}
    50  				if saved != "" {
    51  					saved += "\n\n"
    52  				}
    53  				saved += g
    54  			}
    55  
    56  			fmt.Print(saved)
    57  			return
    58  		}
    59  		buf = make([]byte, 2*len(buf))
    60  	}
    61  }
    62  
    63  func recurseThenCallGo(w chan struct{}, frames int, goroutines int, main bool) {
    64  	if frames == 0 {
    65  		// Signal to TracebackAncestors that we are done recursing and starting goroutines.
    66  		w <- struct{}{}
    67  		<-w
    68  		return
    69  	}
    70  	if goroutines == 0 {
    71  		// Record which goroutine this is so we can ignore it
    72  		// in the traceback if it hasn't finished exiting by
    73  		// the time we printStack.
    74  		if !main {
    75  			ignoreGoroutines[goroutineID()] = true
    76  		}
    77  
    78  		// Start the next goroutine now that there are no more recursions left
    79  		// for this current goroutine.
    80  		go recurseThenCallGo(w, frames-1, numFrames, false)
    81  		return
    82  	}
    83  	recurseThenCallGo(w, frames, goroutines-1, main)
    84  }
    85  
    86  func goroutineID() string {
    87  	buf := make([]byte, 128)
    88  	runtime.Stack(buf, false)
    89  	prefix := []byte("goroutine ")
    90  	var found bool
    91  	if buf, found = bytes.CutPrefix(buf, prefix); !found {
    92  		panic(fmt.Sprintf("expected %q at beginning of traceback:\n%s", prefix, buf))
    93  	}
    94  	id, _, _ := bytes.Cut(buf, []byte(" "))
    95  	return string(id)
    96  }
    97
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