ceph/src/jaegertracing/opentracing-cpp/example/dynamic_load/dynamic_load-example.cpp

   1 // Demonstrates how to load a tracer library in at runtime and how to use it
   2 // to construct spans. To run it using the mocktracer, invoke with
   3 //
   4 //     TRACER_CONFIG=`mktemp`
   5 //     echo '{ "output_file": "/dev/stdout" }' > $TRACER_CONFIG
   6 //     dynamic_load-example /path/to/libopentracing_mocktracer.so $TRACER_CONFIG
   7
   8 #include <opentracing/dynamic_load.h>
   9 #include <cassert>
  10 #include <cerrno>
  11 #include <fstream>
  12 #include <iostream>
  13 #include <iterator>
  14 #include <string>
  15
  16 #ifdef _MSC_VER
  17 #pragma warning(push)
  18 #pragma warning(disable : 4996)
  19 #endif
  20
  21 int main(int argc, char* argv[]) {
  22   if (argc != 3) {
  23     std::cerr << "Usage: <tracer_library> <tracer_config_file>\n";
  24     return -1;
  25   }
  26
  27   // Load the tracer library.
  28   std::string error_message;
  29   auto handle_maybe =
  30       opentracing::DynamicallyLoadTracingLibrary(argv[1], error_message);
  31   if (!handle_maybe) {
  32     std::cerr << "Failed to load tracer library " << error_message << "\n";
  33     return -1;
  34   }
  35
  36   // Read in the tracer's configuration.
  37   std::ifstream istream{argv[2]};
  38   if (!istream.good()) {
  39     std::cerr << "Failed to open tracer config file " << argv[2] << ": "
  40               << std::strerror(errno) << "\n";
  41     return -1;
  42   }
  43   std::string tracer_config{std::istreambuf_iterator<char>{istream},
  44                             std::istreambuf_iterator<char>{}};
  45
  46   // Construct a tracer.
  47   auto& tracer_factory = handle_maybe->tracer_factory();
  48   auto tracer_maybe =
  49       tracer_factory.MakeTracer(tracer_config.c_str(), error_message);
  50   if (!tracer_maybe) {
  51     std::cerr << "Failed to create tracer " << error_message << "\n";
  52     return -1;
  53   }
  54   auto& tracer = *tracer_maybe;
  55
  56   // Use the tracer to create some spans.
  57   {
  58     auto span_a = tracer->StartSpan("A");
  59     assert(span_a != nullptr);
  60     span_a->SetTag("abc", 123);
  61     auto span_b =
  62         tracer->StartSpan("B", {opentracing::ChildOf(&span_a->context())});
  63     assert(span_b != nullptr);
  64     span_b->SetTag("xyz", 987);
  65   }
  66
  67   tracer->Close();
  68   return 0;
  69 }