Added integration support for DataDog APM Tracing

vendor/gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer/spancontext.go

@@ -0,0 +1,193 @@
+package tracer
+
+import (
+	"sync"
+
+	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace"
+	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/internal"
+)
+
+var _ ddtrace.SpanContext = (*spanContext)(nil)
+
+// SpanContext represents a span state that can propagate to descendant spans
+// and across process boundaries. It contains all the information needed to
+// spawn a direct descendant of the span that it belongs to. It can be used
+// to create distributed tracing by propagating it using the provided interfaces.
+type spanContext struct {
+	// the below group should propagate only locally
+
+	trace   *trace // reference to the trace that this span belongs too
+	span    *span  // reference to the span that hosts this context
+	sampled bool   // whether this span will be sampled or not
+
+	// the below group should propagate cross-process
+
+	traceID uint64
+	spanID  uint64
+
+	mu          sync.RWMutex // guards below fields
+	baggage     map[string]string
+	priority    int
+	hasPriority bool
+}
+
+// newSpanContext creates a new SpanContext to serve as context for the given
+// span. If the provided parent is not nil, the context will inherit the trace,
+// baggage and other values from it. This method also pushes the span into the
+// new context's trace and as a result, it should not be called multiple times
+// for the same span.
+func newSpanContext(span *span, parent *spanContext) *spanContext {
+	context := &spanContext{
+		traceID: span.TraceID,
+		spanID:  span.SpanID,
+		sampled: true,
+		span:    span,
+	}
+	if v, ok := span.Metrics[samplingPriorityKey]; ok {
+		context.hasPriority = true
+		context.priority = int(v)
+	}
+	if parent != nil {
+		context.trace = parent.trace
+		context.sampled = parent.sampled
+		context.hasPriority = parent.hasSamplingPriority()
+		context.priority = parent.samplingPriority()
+		parent.ForeachBaggageItem(func(k, v string) bool {
+			context.setBaggageItem(k, v)
+			return true
+		})
+	}
+	if context.trace == nil {
+		context.trace = newTrace()
+	}
+	// put span in context's trace
+	context.trace.push(span)
+	return context
+}
+
+// SpanID implements ddtrace.SpanContext.
+func (c *spanContext) SpanID() uint64 { return c.spanID }
+
+// TraceID implements ddtrace.SpanContext.
+func (c *spanContext) TraceID() uint64 { return c.traceID }
+
+// ForeachBaggageItem implements ddtrace.SpanContext.
+func (c *spanContext) ForeachBaggageItem(handler func(k, v string) bool) {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	for k, v := range c.baggage {
+		if !handler(k, v) {
+			break
+		}
+	}
+}
+
+func (c *spanContext) setSamplingPriority(p int) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.priority = p
+	c.hasPriority = true
+}
+
+func (c *spanContext) samplingPriority() int {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return c.priority
+}
+
+func (c *spanContext) hasSamplingPriority() bool {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return c.hasPriority
+}
+
+func (c *spanContext) setBaggageItem(key, val string) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.baggage == nil {
+		c.baggage = make(map[string]string, 1)
+	}
+	c.baggage[key] = val
+}
+
+func (c *spanContext) baggageItem(key string) string {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return c.baggage[key]
+}
+
+// finish marks this span as finished in the trace.
+func (c *spanContext) finish() { c.trace.ackFinish() }
+
+// trace holds information about a specific trace. This structure is shared
+// between all spans in a trace.
+type trace struct {
+	mu       sync.RWMutex // guards below fields
+	spans    []*span      // all the spans that are part of this trace
+	finished int          // the number of finished spans
+	full     bool         // signifies that the span buffer is full
+}
+
+var (
+	// traceStartSize is the initial size of our trace buffer,
+	// by default we allocate for a handful of spans within the trace,
+	// reasonable as span is actually way bigger, and avoids re-allocating
+	// over and over. Could be fine-tuned at runtime.
+	traceStartSize = 10
+	// traceMaxSize is the maximum number of spans we keep in memory.
+	// This is to avoid memory leaks, if above that value, spans are randomly
+	// dropped and ignore, resulting in corrupted tracing data, but ensuring
+	// original program continues to work as expected.
+	traceMaxSize = int(1e5)
+)
+
+// newTrace creates a new trace using the given callback which will be called
+// upon completion of the trace.
+func newTrace() *trace {
+	return &trace{spans: make([]*span, 0, traceStartSize)}
+}
+
+// push pushes a new span into the trace. If the buffer is full, it returns
+// a errBufferFull error.
+func (t *trace) push(sp *span) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.full {
+		return
+	}
+	if len(t.spans) >= traceMaxSize {
+		// capacity is reached, we will not be able to complete this trace.
+		t.full = true
+		t.spans = nil // GC
+		if tr, ok := internal.GetGlobalTracer().(*tracer); ok {
+			// we have a tracer we can submit errors too.
+			tr.pushError(&spanBufferFullError{})
+		}
+		return
+	}
+	t.spans = append(t.spans, sp)
+}
+
+// ackFinish aknowledges that another span in the trace has finished, and checks
+// if the trace is complete, in which case it calls the onFinish function.
+func (t *trace) ackFinish() {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.full {
+		// capacity has been reached, the buffer is no longer tracking
+		// all the spans in the trace, so the below conditions will not
+		// be accurate and would trigger a pre-mature flush, exposing us
+		// to a race condition where spans can be modified while flushing.
+		return
+	}
+	t.finished++
+	if len(t.spans) != t.finished {
+		return
+	}
+	if tr, ok := internal.GetGlobalTracer().(*tracer); ok {
+		// we have a tracer that can receive completed traces.
+		tr.pushTrace(t.spans)
+	}
+	t.spans = nil
+	t.finished = 0 // important, because a buffer can be used for several flushes
+}