Zhiqiang Xie
--- a/src/client.cc

+ 17

− 4
+++ b/src/client.cc

+ 17

− 4
 @@ -23,6 +23,7 @@
 #include <atomic>
 #include <chrono>
 #include <map>
+#include <iterator>

 #include <grpc/support/log.h>
 #include <grpcpp/grpcpp.h>
 @@ -48,6 +49,8 @@ static struct argp_option options[] = {
  {"topology", 't', "FILE", 0, "A topology file.  This is required.  See config/example_topology.json for an example." },
  {"addresses", 'a', "FILE", 0, "An addresses file.  This is required.  See config/example_addresses.json for an example." },
  {"interval", 'i', "NUM", 0, "Interval size in seconds, default 10.  Each trace will log the interval when it was generated." },
+  // only for opentelemetry based tracers
+  {"sampling",  's', "NUM",  0,  "Probability of head-based sampling. Default 1." },
  { 0 }
 };

 @@ -60,6 +63,7 @@ struct arguments {
  char* service_name;
  char* topology_filename;
  char* addresses_filename;
+  float sampling;
 };

 static error_t parse_opt (int key, char *arg, struct argp_state *state) {
 @@ -88,6 +92,8 @@ static error_t parse_opt (int key, char *arg, struct argp_state *state) {
    case 'a':
      arguments->addresses_filename = arg;
      break;
+    case 's':
+      arguments->sampling = atof(arg);
    case ARGP_KEY_ARG:
      if (state->arg_num >= 1)
        /* Too many arguments. */
 @@ -122,6 +128,7 @@ using opentelemetry::sdk::trace::IdGenerator;
 using opentelemetry::sdk::trace::RandomIdGenerator;

 bool debug;
+float sample_probability;

 uint32_t max_requests;
 uint32_t initial_requests;
 @@ -167,8 +174,8 @@ class HindsightGRPCClient {
    request.mutable_otel()->set_trace_id(std::string(tid_buffer, 32));
    // special span id
    request.mutable_otel()->set_span_id(std::string("ffffffffffffffff"));
-    // todo: command for head-based sampling policy
-    request.mutable_otel()->set_sample(true);
+    // set the sample flag with probability specified by user commands
+    request.mutable_otel()->set_sample(rand() / sample_probability > RAND_MAX ? false : true);

    // truncate the first 64 bits to fit into hindsight
    uint64_t trace_id = *((uint64_t*) tid_raw.Id().data());
 @@ -233,8 +240,11 @@ class HindsightGRPCClient {

      // Submit next call
      if (max_requests == 0 || sent_count < max_requests) {
-        std::string api_name = apis_.begin()->first;
-        Exec(api_name, flag_r); // The actual RPC call!
+        // std::string api_name = apis_.begin()->first;
+        // Exec(api_name, flag_r); // The actual RPC call!
+        auto api_iter = apis_.begin();
+        std::advance(api_iter, rand() % apis_.size());
+        Exec(api_iter->first, flag_r); // The actual RPC call!
      } else if (received_count < max_requests) {
        continue;
      } else {
 @@ -305,10 +315,13 @@ int main(int argc, char** argv) {
  arguments.topology_filename = NULL;
  arguments.addresses_filename = NULL;
  arguments.interval = 10;
+  arguments.sampling = 1;

  /* Parse the arguments */
  argp_parse (&argp, argc, argv, 0, 0, &arguments);

+  sample_probability = arguments.sampling;
+
  /* If 'standalone' is specified as the service name, it is a special case */
  if (strcmp(arguments.service_name, "standalone") == 0) {
    std::cout << "Using the built-in standalone configuration" << std::endl;