Instana tracer implementation

vendor/github.com/opentracing/basictracer-go/debug.go

@@ -0,0 +1,78 @@
+package basictracer
+
+import (
+	"bytes"
+	"fmt"
+	"runtime"
+	"strconv"
+	"sync"
+)
+
+const debugGoroutineIDTag = "_initial_goroutine"
+
+type errAssertionFailed struct {
+	span *spanImpl
+	msg  string
+}
+
+// Error implements the error interface.
+func (err *errAssertionFailed) Error() string {
+	return fmt.Sprintf("%s:\n%+v", err.msg, err.span)
+}
+
+func (s *spanImpl) Lock() {
+	s.Mutex.Lock()
+	s.maybeAssertSanityLocked()
+}
+
+func (s *spanImpl) maybeAssertSanityLocked() {
+	if s.tracer == nil {
+		s.Mutex.Unlock()
+		panic(&errAssertionFailed{span: s, msg: "span used after call to Finish()"})
+	}
+	if s.tracer.options.DebugAssertSingleGoroutine {
+		startID := curGoroutineID()
+		curID, ok := s.raw.Tags[debugGoroutineIDTag].(uint64)
+		if !ok {
+			// This is likely invoked in the context of the SetTag which sets
+			// debugGoroutineTag.
+			return
+		}
+		if startID != curID {
+			s.Mutex.Unlock()
+			panic(&errAssertionFailed{
+				span: s,
+				msg:  fmt.Sprintf("span started on goroutine %d, but now running on %d", startID, curID),
+			})
+		}
+	}
+}
+
+var goroutineSpace = []byte("goroutine ")
+var littleBuf = sync.Pool{
+	New: func() interface{} {
+		buf := make([]byte, 64)
+		return &buf
+	},
+}
+
+// Credit to @bradfitz:
+// https://github.com/golang/net/blob/master/http2/gotrack.go#L51
+func curGoroutineID() uint64 {
+	bp := littleBuf.Get().(*[]byte)
+	defer littleBuf.Put(bp)
+	b := *bp
+	b = b[:runtime.Stack(b, false)]
+	// Parse the 4707 out of "goroutine 4707 ["
+	b = bytes.TrimPrefix(b, goroutineSpace)
+	i := bytes.IndexByte(b, ' ')
+	if i < 0 {
+		panic(fmt.Sprintf("No space found in %q", b))
+	}
+	b = b[:i]
+	n, err := strconv.ParseUint(string(b), 10, 64)
+	if err != nil {
+		panic(fmt.Sprintf("Failed to parse goroutine ID out of %q: %v", b, err))
+	}
+	return n
+}