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package tracer
import (
"errors"
"log"
"os"
"strconv"
"time"
"gopkg.in/DataDog/dd-trace-go.v1/ddtrace"
"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/ext"
"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/internal"
)
var _ ddtrace.Tracer = (*tracer)(nil)
// tracer creates, buffers and submits Spans which are used to time blocks of
// computation. They are accumulated and streamed into an internal payload,
// which is flushed to the agent whenever its size exceeds a specific threshold
// or when a certain interval of time has passed, whichever happens first.
//
// tracer operates based on a worker loop which responds to various request
// channels. It additionally holds two buffers which accumulates error and trace
// queues to be processed by the payload encoder.
type tracer struct {
*config
*payload
flushAllReq chan chan<- struct{}
flushTracesReq chan struct{}
flushErrorsReq chan struct{}
exitReq chan struct{}
payloadQueue chan []*span
errorBuffer chan error
// stopped is a channel that will be closed when the worker has exited.
stopped chan struct{}
// syncPush is used for testing. When non-nil, it causes pushTrace to become
// a synchronous (blocking) operation, meaning that it will only return after
// the trace has been fully processed and added onto the payload.
syncPush chan struct{}
}
const (
// flushInterval is the interval at which the payload contents will be flushed
// to the transport.
flushInterval = 2 * time.Second
// payloadMaxLimit is the maximum payload size allowed and should indicate the
// maximum size of the package that the agent can receive.
payloadMaxLimit = 9.5 * 1024 * 1024 // 9.5 MB
// payloadSizeLimit specifies the maximum allowed size of the payload before
// it will trigger a flush to the transport.
payloadSizeLimit = payloadMaxLimit / 2
)
// Start starts the tracer with the given set of options. It will stop and replace
// any running tracer, meaning that calling it several times will result in a restart
// of the tracer by replacing the current instance with a new one.
func Start(opts ...StartOption) {
if internal.Testing {
return // mock tracer active
}
internal.SetGlobalTracer(newTracer(opts...))
}
// Stop stops the started tracer. Subsequent calls are valid but become no-op.
func Stop() {
internal.SetGlobalTracer(&internal.NoopTracer{})
}
// Span is an alias for ddtrace.Span. It is here to allow godoc to group methods returning
// ddtrace.Span. It is recommended and is considered more correct to refer to this type as
// ddtrace.Span instead.
type Span = ddtrace.Span
// StartSpan starts a new span with the given operation name and set of options.
// If the tracer is not started, calling this function is a no-op.
func StartSpan(operationName string, opts ...StartSpanOption) Span {
return internal.GetGlobalTracer().StartSpan(operationName, opts...)
}
// Extract extracts a SpanContext from the carrier. The carrier is expected
// to implement TextMapReader, otherwise an error is returned.
// If the tracer is not started, calling this function is a no-op.
func Extract(carrier interface{}) (ddtrace.SpanContext, error) {
return internal.GetGlobalTracer().Extract(carrier)
}
// Inject injects the given SpanContext into the carrier. The carrier is
// expected to implement TextMapWriter, otherwise an error is returned.
// If the tracer is not started, calling this function is a no-op.
func Inject(ctx ddtrace.SpanContext, carrier interface{}) error {
return internal.GetGlobalTracer().Inject(ctx, carrier)
}
const (
// payloadQueueSize is the buffer size of the trace channel.
payloadQueueSize = 1000
// errorBufferSize is the buffer size of the error channel.
errorBufferSize = 200
)
func newTracer(opts ...StartOption) *tracer {
c := new(config)
defaults(c)
for _, fn := range opts {
fn(c)
}
if c.transport == nil {
c.transport = newTransport(c.agentAddr, c.httpRoundTripper)
}
if c.propagator == nil {
c.propagator = NewPropagator(nil)
}
t := &tracer{
config: c,
payload: newPayload(),
flushAllReq: make(chan chan<- struct{}),
flushTracesReq: make(chan struct{}, 1),
flushErrorsReq: make(chan struct{}, 1),
exitReq: make(chan struct{}),
payloadQueue: make(chan []*span, payloadQueueSize),
errorBuffer: make(chan error, errorBufferSize),
stopped: make(chan struct{}),
}
go t.worker()
return t
}
// worker receives finished traces to be added into the payload, as well
// as periodically flushes traces to the transport.
func (t *tracer) worker() {
defer close(t.stopped)
ticker := time.NewTicker(flushInterval)
defer ticker.Stop()
for {
select {
case trace := <-t.payloadQueue:
t.pushPayload(trace)
case <-ticker.C:
t.flush()
case done := <-t.flushAllReq:
t.flush()
done <- struct{}{}
case <-t.flushTracesReq:
t.flushTraces()
case <-t.flushErrorsReq:
t.flushErrors()
case <-t.exitReq:
t.flush()
return
}
}
}
func (t *tracer) pushTrace(trace []*span) {
select {
case <-t.stopped:
return
default:
}
select {
case t.payloadQueue <- trace:
default:
t.pushError(&dataLossError{
context: errors.New("payload queue full, dropping trace"),
count: len(trace),
})
}
if t.syncPush != nil {
// only in tests
<-t.syncPush
}
}
func (t *tracer) pushError(err error) {
select {
case <-t.stopped:
return
default:
}
if len(t.errorBuffer) >= cap(t.errorBuffer)/2 { // starts being full, anticipate, try and flush soon
select {
case t.flushErrorsReq <- struct{}{}:
default: // a flush was already requested, skip
}
}
select {
case t.errorBuffer <- err:
default:
// OK, if we get this, our error error buffer is full,
// we can assume it is filled with meaningful messages which
// are going to be logged and hopefully read, nothing better
// we can do, blocking would make things worse.
}
}
// StartSpan creates, starts, and returns a new Span with the given `operationName`.
func (t *tracer) StartSpan(operationName string, options ...ddtrace.StartSpanOption) ddtrace.Span {
var opts ddtrace.StartSpanConfig
for _, fn := range options {
fn(&opts)
}
var startTime int64
if opts.StartTime.IsZero() {
startTime = now()
} else {
startTime = opts.StartTime.UnixNano()
}
var context *spanContext
if opts.Parent != nil {
if ctx, ok := opts.Parent.(*spanContext); ok {
context = ctx
}
}
id := random.Uint64()
// span defaults
span := &span{
Name: operationName,
Service: t.config.serviceName,
Resource: operationName,
Meta: map[string]string{},
Metrics: map[string]float64{},
SpanID: id,
TraceID: id,
ParentID: 0,
Start: startTime,
}
if context != nil {
// this is a child span
span.TraceID = context.traceID
span.ParentID = context.spanID
if context.hasSamplingPriority() {
span.Metrics[samplingPriorityKey] = float64(context.samplingPriority())
}
if context.span != nil {
// it has a local parent, inherit the service
context.span.RLock()
span.Service = context.span.Service
context.span.RUnlock()
}
}
span.context = newSpanContext(span, context)
if context == nil || context.span == nil {
// this is either a root span or it has a remote parent, we should add the PID.
span.SetTag(ext.Pid, strconv.Itoa(os.Getpid()))
}
// add tags from options
for k, v := range opts.Tags {
span.SetTag(k, v)
}
// add global tags
for k, v := range t.config.globalTags {
span.SetTag(k, v)
}
if context == nil {
// this is a brand new trace, sample it
t.sample(span)
}
return span
}
// Stop stops the tracer.
func (t *tracer) Stop() {
select {
case <-t.stopped:
return
default:
t.exitReq <- struct{}{}
<-t.stopped
}
}
// Inject uses the configured or default TextMap Propagator.
func (t *tracer) Inject(ctx ddtrace.SpanContext, carrier interface{}) error {
return t.config.propagator.Inject(ctx, carrier)
}
// Extract uses the configured or default TextMap Propagator.
func (t *tracer) Extract(carrier interface{}) (ddtrace.SpanContext, error) {
return t.config.propagator.Extract(carrier)
}
// flushTraces will push any currently buffered traces to the server.
func (t *tracer) flushTraces() {
if t.payload.itemCount() == 0 {
return
}
size, count := t.payload.size(), t.payload.itemCount()
if t.config.debug {
log.Printf("Sending payload: size: %d traces: %d\n", size, count)
}
rc, err := t.config.transport.send(t.payload)
if err != nil {
t.pushError(&dataLossError{context: err, count: count})
}
if err == nil && t.config.prioritySampling != nil {
t.config.prioritySampling.readRatesJSON(rc) // TODO: handle error?
}
t.payload.reset()
}
// flushErrors will process log messages that were queued
func (t *tracer) flushErrors() {
logErrors(t.errorBuffer)
}
func (t *tracer) flush() {
t.flushTraces()
t.flushErrors()
}
// forceFlush forces a flush of data (traces and services) to the agent.
// Flushes are done by a background task on a regular basis, so you never
// need to call this manually, mostly useful for testing and debugging.
func (t *tracer) forceFlush() {
done := make(chan struct{})
t.flushAllReq <- done
<-done
}
// pushPayload pushes the trace onto the payload. If the payload becomes
// larger than the threshold as a result, it sends a flush request.
func (t *tracer) pushPayload(trace []*span) {
if err := t.payload.push(trace); err != nil {
t.pushError(&traceEncodingError{context: err})
}
if t.payload.size() > payloadSizeLimit {
// getting large
select {
case t.flushTracesReq <- struct{}{}:
default:
// flush already queued
}
}
if t.syncPush != nil {
// only in tests
t.syncPush <- struct{}{}
}
}
// sampleRateMetricKey is the metric key holding the applied sample rate. Has to be the same as the Agent.
const sampleRateMetricKey = "_sample_rate"
// Sample samples a span with the internal sampler.
func (t *tracer) sample(span *span) {
sampler := t.config.sampler
sampled := sampler.Sample(span)
span.context.sampled = sampled
if !sampled {
return
}
if rs, ok := sampler.(RateSampler); ok && rs.Rate() < 1 {
// the span was sampled using a rate sampler which wasn't all permissive,
// so we make note of the sampling rate.
span.Lock()
defer span.Unlock()
if span.finished {
// we don't touch finished span as they might be flushing
return
}
span.Metrics[sampleRateMetricKey] = rs.Rate()
}
if t.config.prioritySampling != nil {
t.config.prioritySampling.apply(span)
}
}
|