add Tracer level sample rate

Author: flier

examples/grpc_greeter/greeter_client.cc

@@ -94,16 +94,17 @@ class GreeterClient
 
         if (span.parent_id())
             send_header(ZIPKIN_X_PARENT_SPAN_ID, folly::to<std::string>(span.parent_id()));
-
+        if (span.sampled())
+            send_header(ZIPKIN_X_SAMPLED, "1");
         if (span.debug())
             send_header(ZIPKIN_X_FLAGS, "1");
 
-        span << zipkin::TraceKeys::CLIENT_SEND;
+        span << zipkin::TraceKeys::CLIENT_SEND << endpoint;
 
         // The actual RPC.
         Status status = stub_->SayHello(&context, request, &reply);
 
-        span << zipkin::TraceKeys::CLIENT_RECV;
+        span << zipkin::TraceKeys::CLIENT_RECV << endpoint;
 
         // Act upon its status.
         if (status.ok())

examples/simple_proxy/main.c

@@ -212,6 +212,10 @@ void forward_http_request(struct mg_connection *nc, struct http_message *hm)
     {
       p += snprintf(p, end - p, ZIPKIN_X_PARENT_SPAN_ID ": " ZIPKIN_SPAN_ID_FMT CRLF, zipkin_span_parent_id(span));
     }
+    if (zipkin_span_sampled(span))
+    {
+      p += snprintf(p, end - p, ZIPKIN_X_SAMPLED ": 1" CRLF);
+    }
     if (zipkin_span_debug(span))
     {
       p += snprintf(p, end - p, ZIPKIN_X_FLAGS ": 1" CRLF);
@@ -283,6 +287,10 @@ void reply_json_response(struct mg_connection *nc, struct http_message *hm)
     {
       zipkin_span_set_parent_id(span, strtoull(hv->p, NULL, 16));
     }
+    else if (0 == mg_vcmp(hn, ZIPKIN_X_SAMPLED))
+    {
+      zipkin_span_set_sampled(span, strtoul(hv->p, NULL, 10));
+    }
 
     mg_printf(nc, "%s\"%.*s\": \"%.*s\"", (i != 0 ? "," : ""), (int)hn->len, hn->p, (int)hv->len, hv->p);
   }

include/zipkin.h

@@ -114,6 +114,9 @@ zipkin_span_t zipkin_span_parse_trace_id(zipkin_span_t span, const char *str, si
 
 int zipkin_span_debug(zipkin_span_t span);
 
+int zipkin_span_sampled(zipkin_span_t span);
+zipkin_span_t zipkin_span_set_sampled(zipkin_span_t span, int sampled);
+
 zipkin_userdata_t zipkin_span_userdata(zipkin_span_t span);
 zipkin_span_t zipkin_span_set_userdata(zipkin_span_t span, zipkin_userdata_t userdata);
 

src/CApi.cpp

@@ -142,6 +142,17 @@ int zipkin_span_debug(zipkin_span_t span)
 {
     return span ? static_cast<zipkin::Span *>(span)->debug() : false;
 }
+int zipkin_span_sampled(zipkin_span_t span)
+{
+    return span ? static_cast<zipkin::Span *>(span)->sampled() : false;
+}
+zipkin_span_t zipkin_span_set_sampled(zipkin_span_t span, int sampled)
+{
+    if (span)
+        static_cast<zipkin::Span *>(span)->with_sampled(sampled);
+
+    return span;
+}
 zipkin_userdata_t zipkin_span_userdata(zipkin_span_t span)
 {
     if (span)

src/Span.cpp

@@ -230,7 +230,7 @@ const std::string decode(const std::string &encoded_string)
 
 } // namespace base64
 
-Span::Span(Tracer *tracer, const std::string &name, span_id_t parent_id, userdata_t userdata) : m_tracer(tracer)
+Span::Span(Tracer *tracer, const std::string &name, span_id_t parent_id, userdata_t userdata, bool sampled) : m_tracer(tracer)
 {
     if (tracer)
     {
@@ -242,10 +242,10 @@ Span::Span(Tracer *tracer, const std::string &name, span_id_t parent_id, userdat
         }
     }
 
-    reset(name, parent_id, userdata);
+    reset(name, parent_id, userdata, sampled);
 }
 
-void Span::reset(const std::string &name, span_id_t parent_id, userdata_t userdata)
+void Span::reset(const std::string &name, span_id_t parent_id, userdata_t userdata, bool sampled)
 {
     m_span.__isset = _Span__isset();
     m_span.__set_name(name);
@@ -260,6 +260,7 @@ void Span::reset(const std::string &name, span_id_t parent_id, userdata_t userda
     }
 
     m_userdata = userdata;
+    m_sampled = sampled;
 }
 
 void Span::submit(void)

src/Span.h

@@ -538,19 +538,20 @@ class Span
     Tracer *m_tracer;
     ::Span m_span;
     userdata_t m_userdata;
+    bool m_sampled;
 
     static const ::Endpoint host(const Endpoint *endpoint);
 
   public:
     /**
      * \brief Construct a span
      */
-    Span(Tracer *tracer, const std::string &name, span_id_t parent_id = 0, userdata_t userdata = nullptr);
+    Span(Tracer *tracer, const std::string &name, span_id_t parent_id = 0, userdata_t userdata = nullptr, bool sampled = true);
 
     /**
      * \brief Reset a span
      */
-    void reset(const std::string &name, span_id_t parent_id = 0, userdata_t userdata = nullptr);
+    void reset(const std::string &name, span_id_t parent_id = 0, userdata_t userdata = nullptr, bool sampled = true);
 
     /**
      * \brief Submit a Span to Tracer
@@ -705,6 +706,18 @@ class Span
         return *this;
     }
 
+    /**
+    * \brief Report this span to the tracing system
+    */
+    inline bool sampled(void) const { return m_sampled; }
+
+    /** \sa Span#sampled */
+    inline Span &with_sampled(bool sampled = true)
+    {
+        m_sampled = sampled;
+        return *this;
+    }
+
     virtual inline Span *span(const std::string &name, userdata_t userdata = nullptr) const
     {
         return new Span(m_tracer, name, m_span.id, userdata ? userdata : m_userdata);

src/Tracer.cpp

@@ -28,12 +28,14 @@ Span *CachedTracer::span(const std::string &name, span_id_t parent_id, void *use
         span = new (this) CachedSpan(this, name, parent_id, userdata);
     }
 
+    span->with_sampled(m_total_spans++ % m_sample_rate == 0);
+
     return span;
 }
 
 void CachedTracer::submit(Span *span)
 {
-    if (m_collector)
+    if (m_collector && span->sampled())
     {
         VLOG(2) << "Span @ " << span << " submited to collector @ " << m_collector << ", id=" << span->id();
 

src/Tracer.h

@@ -2,6 +2,7 @@
 
 #include <cstddef>
 #include <string>
+#include <atomic>
 
 #include <boost/lockfree/stack.hpp>
 
@@ -50,6 +51,14 @@ struct Tracer
     */
     virtual const std::string &name(void) const = 0;
 
+    /**
+    * \brief Tracer sample rate
+    */
+    virtual size_t sample_rate(void) const = 0;
+
+    /** \sa Tracer#sample_rate */
+    virtual void set_sample_rate(size_t sample_rate) = 0;
+
     /**
      * \brief Associated Collector
      */
@@ -135,6 +144,8 @@ class CachedTracer : public Tracer
 
     trace_id_t m_id, m_id_high;
     const std::string m_name;
+    size_t m_sample_rate;
+    std::atomic_size_t m_total_spans;
 
   public:
     typedef SpanCache<64> span_cache_t;
@@ -144,7 +155,7 @@ class CachedTracer : public Tracer
 
   public:
     CachedTracer(Collector *collector, const std::string &name, size_t cache_message_size = default_cache_message_size)
-        : m_collector(collector), m_id(Span::next_id()), m_id_high(0), m_name(name), m_cache(cache_message_size)
+        : m_collector(collector), m_id(Span::next_id()), m_id_high(0), m_name(name), m_sample_rate(1), m_cache(cache_message_size)
     {
     }
 
@@ -165,6 +176,9 @@ class CachedTracer : public Tracer
         m_id_high = id.first;
     }
     virtual const std::string &name(void) const override { return m_name; }
+    virtual size_t sample_rate(void) const override { return m_sample_rate; }
+    virtual void set_sample_rate(size_t sample_rate) override { m_sample_rate = sample_rate; }
+
     virtual Collector *collector(void) const override { return m_collector; }
 
     virtual Span *span(const std::string &name, span_id_t parent_id = 0, void *userdata = nullptr) override;

test/Mocks.hpp

@@ -23,6 +23,10 @@ class MockTracer : public zipkin::Tracer
 
   MOCK_CONST_METHOD0(name, const std::string &(void));
 
+  MOCK_CONST_METHOD0(sample_rate, size_t(void));
+
+  MOCK_METHOD1(set_sample_rate, void(size_t sample_rate));
+
   MOCK_CONST_METHOD0(collector, zipkin::Collector *(void));
 
   MOCK_METHOD3(span, zipkin::Span *(const std::string &, span_id_t, userdata_t));