/
tracer.go
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/
tracer.go
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// Unless explicitly stated otherwise all files in this repository are licensed
// under the Apache License Version 2.0.
// This product includes software developed at Datadog (https://www.datadoghq.com/).
// Copyright 2016 Datadog, Inc.
package tracer
import (
"encoding/json"
"fmt"
"net/http"
"os"
"strconv"
"sync"
"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"
"gopkg.in/DataDog/dd-trace-go.v1/internal/log"
)
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 *config
// features holds the capabilities of the agent and determines some
// of the behaviour of the tracer.
features *agentFeatures
// stats specifies the concentrator used to compute statistics, when client-side
// stats are enabled.
stats *concentrator
// traceWriter is responsible for sending finished traces to their
// destination, such as the Trace Agent or Datadog Forwarder.
traceWriter traceWriter
// out receives traces to be added to the payload.
out chan []*span
// flush receives a channel onto which it will confirm after a flush has been
// triggered and completed.
flush chan chan<- struct{}
// stop causes the tracer to shut down when closed.
stop chan struct{}
// stopOnce ensures the tracer is stopped exactly once.
stopOnce sync.Once
// wg waits for all goroutines to exit when stopping.
wg sync.WaitGroup
// prioritySampling holds an instance of the priority sampler.
prioritySampling *prioritySampler
// pid of the process
pid string
// These integers track metrics about spans and traces as they are started,
// finished, and dropped
spansStarted, spansFinished, tracesDropped int64
// Records the number of dropped P0 traces and spans.
droppedP0Traces, droppedP0Spans uint64
// rulesSampling holds an instance of the rules sampler. These are user-defined
// rules for applying a sampling rate to spans that match the designated service
// or operation name.
rulesSampling *rulesSampler
}
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
// concurrentConnectionLimit specifies the maximum number of concurrent outgoing
// connections allowed.
concurrentConnectionLimit = 100
)
// statsInterval is the interval at which health metrics will be sent with the
// statsd client; replaced in tests.
var statsInterval = 10 * time.Second
// 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
}
t := newTracer(opts...)
if t.config.HasFeature("discovery") {
t.loadAgentFeatures()
}
internal.SetGlobalTracer(t)
if t.config.logStartup {
logStartup(t)
}
}
// Stop stops the started tracer. Subsequent calls are valid but become no-op.
func Stop() {
internal.SetGlobalTracer(&internal.NoopTracer{})
log.Flush()
}
// 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)
}
// payloadQueueSize is the buffer size of the trace channel.
const payloadQueueSize = 1000
func newUnstartedTracer(opts ...StartOption) *tracer {
c := newConfig(opts...)
envRules, err := samplingRulesFromEnv()
if err != nil {
log.Warn("DIAGNOSTICS Error(s) parsing DD_TRACE_SAMPLING_RULES: %s", err)
}
if envRules != nil {
c.samplingRules = envRules
}
sampler := newPrioritySampler()
var writer traceWriter
if c.logToStdout {
writer = newLogTraceWriter(c)
} else {
writer = newAgentTraceWriter(c, sampler)
}
t := &tracer{
config: c,
traceWriter: writer,
out: make(chan []*span, payloadQueueSize),
stop: make(chan struct{}),
flush: make(chan chan<- struct{}),
rulesSampling: newRulesSampler(c.samplingRules),
prioritySampling: sampler,
pid: strconv.Itoa(os.Getpid()),
features: &agentFeatures{},
stats: newConcentrator(c, defaultStatsBucketSize),
}
return t
}
func newTracer(opts ...StartOption) *tracer {
t := newUnstartedTracer(opts...)
c := t.config
t.config.statsd.Incr("datadog.tracer.started", nil, 1)
if c.runtimeMetrics {
log.Debug("Runtime metrics enabled.")
t.wg.Add(1)
go func() {
defer t.wg.Done()
t.reportRuntimeMetrics(defaultMetricsReportInterval)
}()
}
t.wg.Add(1)
go func() {
defer t.wg.Done()
tick := t.config.tickChan
if tick == nil {
ticker := time.NewTicker(flushInterval)
defer ticker.Stop()
tick = ticker.C
}
t.worker(tick)
}()
t.wg.Add(1)
go func() {
defer t.wg.Done()
t.reportHealthMetrics(statsInterval)
}()
t.stats.Start()
return t
}
// Flush flushes any buffered traces. Flush is in effect only if a tracer
// is started. Users do not have to call Flush in order to ensure that
// traces reach Datadog. It is a convenience method dedicated to a specific
// use case described below.
//
// Flush is of use in Lambda environments, where starting and stopping
// the tracer on each invokation may create too much latency. In this
// scenario, a tracer may be started and stopped by the parent process
// whereas the invokation can make use of Flush to ensure any created spans
// reach the agent.
func Flush() {
if t, ok := internal.GetGlobalTracer().(*tracer); ok {
t.flushSync()
}
}
// flushSync triggers a flush and waits for it to complete.
func (t *tracer) flushSync() {
done := make(chan struct{})
t.flush <- done
<-done
}
// agentFeatures holds information about the trace-agent's capabilities.
type agentFeatures struct {
mu sync.RWMutex
// DropP0s reports whether it's ok for the tracer to not send any
// P0 traces to the agent.
DropP0s bool
// V05 reports whether it's ok to use the /v0.5/traces endpoint format.
V05 bool // TODO(x): Not yet implemented
// Stats reports whether the agent can receive client-computed stats on
// the /v0.6/stats endpoint.
Stats bool
}
// Load returns the current features.
func (f *agentFeatures) Load() agentFeatures {
f.mu.RLock()
out := *f
f.mu.RUnlock()
return out
}
// Store stores the new features.
func (f *agentFeatures) Store(newf agentFeatures) {
f.mu.Lock()
f.DropP0s = newf.DropP0s
f.V05 = newf.V05
f.Stats = newf.Stats
f.mu.Unlock()
}
// loadAgentFeatures queries the trace-agent for its capabilities and updates
// the tracer's behaviour.
func (t *tracer) loadAgentFeatures() {
if t.config.logToStdout {
// there is no agent
return
}
resp, err := http.Get(fmt.Sprintf("http://%s/info", t.config.agentAddr))
if err != nil {
log.Error("Loading features: %v", err)
return
}
if resp.StatusCode == http.StatusNotFound {
// agent is older than 7.28.0, features not discoverable
t.features.Store(agentFeatures{})
return
}
defer resp.Body.Close()
type infoResponse struct {
Endpoints []string `json:"endpoints"`
ClientDropP0s bool `json:"client_drop_p0s"`
}
var info infoResponse
if err := json.NewDecoder(resp.Body).Decode(&info); err != nil {
log.Error("Decoding features: %v", err)
return
}
f := agentFeatures{DropP0s: info.ClientDropP0s}
for _, endpoint := range info.Endpoints {
switch endpoint {
case "/v0.6/stats":
f.Stats = true
case "/v0.5/traces":
f.V05 = true
}
}
t.features.Store(f)
}
// worker receives finished traces to be added into the payload, as well
// as periodically flushes traces to the transport.
func (t *tracer) worker(tick <-chan time.Time) {
for {
select {
case trace := <-t.out:
t.traceWriter.add(trace)
case <-tick:
t.config.statsd.Incr("datadog.tracer.flush_triggered", []string{"reason:scheduled"}, 1)
t.traceWriter.flush()
case done := <-t.flush:
t.config.statsd.Incr("datadog.tracer.flush_triggered", []string{"reason:invoked"}, 1)
t.traceWriter.flush()
// TODO(x): In reality, the traceWriter.flush() call is not synchronous
// when using the agent traceWriter. However, this functionnality is used
// in Lambda so for that purpose this mechanism should suffice.
done <- struct{}{}
case <-t.stop:
loop:
// the loop ensures that the payload channel is fully drained
// before the final flush to ensure no traces are lost (see #526)
for {
select {
case trace := <-t.out:
t.traceWriter.add(trace)
default:
break loop
}
}
return
}
}
}
func (t *tracer) pushTrace(trace []*span) {
select {
case <-t.stop:
return
default:
}
select {
case t.out <- trace:
default:
log.Error("payload queue full, dropping %d traces", len(trace))
}
}
// 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 := opts.SpanID
if id == 0 {
id = random.Uint64()
}
// span defaults
span := &span{
Name: operationName,
Service: t.config.serviceName,
Resource: operationName,
SpanID: id,
TraceID: id,
Start: startTime,
taskEnd: startExecutionTracerTask(operationName),
noDebugStack: t.config.noDebugStack,
}
if t.config.hostname != "" {
span.setMeta(keyHostname, t.config.hostname)
}
if context != nil {
// this is a child span
span.TraceID = context.traceID
span.ParentID = context.spanID
if p, ok := context.samplingPriority(); ok {
span.setMetric(keySamplingPriority, float64(p))
}
if context.span != nil {
// local parent, inherit service
context.span.RLock()
span.Service = context.span.Service
context.span.RUnlock()
} else {
// remote parent
if context.origin != "" {
// mark origin
span.setMeta(keyOrigin, context.origin)
}
}
}
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.setMeta(ext.Pid, t.pid)
if _, ok := opts.Tags[ext.ServiceName]; !ok && t.config.runtimeMetrics {
// this is a root span in the global service; runtime metrics should
// be linked to it:
span.setMeta("language", "go")
}
}
// 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 || context.span == nil || context.span.Service != span.Service {
span.setMetric(keyTopLevel, 1)
// all top level spans are measured. So the measured tag is redundant.
delete(span.Metrics, keyMeasured)
}
if t.config.version != "" && span.Service == t.config.serviceName {
span.SetTag(ext.Version, t.config.version)
}
if t.config.env != "" {
span.SetTag(ext.Environment, t.config.env)
}
if context == nil {
// this is a brand new trace, sample it
t.sample(span)
}
log.Debug("Started Span: %v, Operation: %s, Resource: %s, Tags: %v, %v", span, span.Name, span.Resource, span.Meta, span.Metrics)
return span
}
// Stop stops the tracer.
func (t *tracer) Stop() {
t.stopOnce.Do(func() {
close(t.stop)
t.config.statsd.Incr("datadog.tracer.stopped", nil, 1)
})
t.stats.Stop()
t.wg.Wait()
t.traceWriter.stop()
t.config.statsd.Close()
}
// 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)
}
// 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) {
if _, ok := span.context.samplingPriority(); ok {
// sampling decision was already made
return
}
sampler := t.config.sampler
if !sampler.Sample(span) {
span.context.drop = true
return
}
if rs, ok := sampler.(RateSampler); ok && rs.Rate() < 1 {
span.setMetric(sampleRateMetricKey, rs.Rate())
}
if t.rulesSampling.apply(span) {
return
}
t.prioritySampling.apply(span)
}