Added example for batch span processor (open-telemetry#241)

examples/CMakeLists.txt

@@ -1,2 +1,3 @@
 add_subdirectory(plugin)
 add_subdirectory(simple)
+add_subdirectory(batch)

examples/batch/BUILD

@@ -0,0 +1,12 @@
+cc_binary(
+    name = "example_simple",
+    srcs = [
+        "main.cc",
+    ],
+    linkopts = ["-lpthread"],
+    deps = [
+        "//api",
+        "//exporters/ostream:ostream_span_exporter",
+        "//sdk/src/trace",
+    ],
+)

examples/batch/CMakeLists.txt

@@ -0,0 +1,6 @@
+include_directories(${CMAKE_SOURCE_DIR}/exporters/ostream/include)
+
+add_executable(batch_span_processor_example main.cc)
+
+target_link_libraries(batch_span_processor_example ${CMAKE_THREAD_LIBS_INIT}
+                      opentelemetry_exporter_ostream_span opentelemetry_trace)

examples/batch/main.cc

@@ -0,0 +1,81 @@
+#include "opentelemetry/sdk/trace/tracer_provider.h"
+#include "opentelemetry/trace/provider.h"
+// Using an exporter that simply dumps span data to stdout.
+#include "opentelemetry/exporters/ostream/span_exporter.h"
+#include "opentelemetry/sdk/trace/batch_span_processor.h"
+
+#include <chrono>
+#include <thread>
+
+constexpr int kNumSpans = 10;
+
+namespace
+{
+
+void initTracer()
+{
+  auto exporter = std::unique_ptr<sdktrace::SpanExporter>(
+      new opentelemetry::exporter::trace::OStreamSpanExporter);
+
+  // CONFIGURE BATCH SPAN PROCESSOR PARAMETERS
+
+  // We make the queue size `KNumSpans`*2+5 because when the queue is half full, a preemptive notif
+  // is sent to start an export call, which we want to avoid in this simple example.
+  const size_t max_queue_size = kNumSpans * 2 + 5;
+
+  // Time interval (in ms) between two consecutive exports.
+  const std::chrono::milliseconds schedule_delay_millis = std::chrono::milliseconds(3000);
+
+  // We export `kNumSpans` after every `schedule_delay_millis` milliseconds.
+  const size_t max_export_batch_size = kNumSpans;
+
+  auto processor = std::shared_ptr<sdktrace::SpanProcessor>(new sdktrace::BatchSpanProcessor(
+      std::move(exporter), max_queue_size, schedule_delay_millis, max_export_batch_size));
+
+  auto provider = nostd::shared_ptr<opentelemetry::trace::TracerProvider>(
+      new sdktrace::TracerProvider(processor));
+  // Set the global trace provider.
+  opentelemetry::trace::Provider::SetTracerProvider(provider);
+}
+
+nostd::shared_ptr<opentelemetry::trace::Tracer> get_tracer()
+{
+  auto provider = opentelemetry::trace::Provider::GetTracerProvider();
+  return provider->GetTracer("foo_library");
+}
+
+void StartAndEndSpans()
+{
+  for (int i = 1; i <= kNumSpans; ++i)
+  {
+    get_tracer()->StartSpan("Span " + std::to_string(i));
+  }
+}
+
+}  // namespace
+
+int main()
+{
+  // Removing this line will leave the default noop TracerProvider in place.
+  initTracer();
+
+  std::cout << "Creating first batch of " << kNumSpans << " spans and waiting 3 seconds ...\n";
+  StartAndEndSpans();
+  std::this_thread::sleep_for(std::chrono::milliseconds(3000 + 50));
+  // The spans should now be exported.
+  std::cout << "....Exported!\n\n\n";
+
+  // Do the same again
+  std::cout << "Creating second batch of " << kNumSpans << " spans and waiting 3 seconds ...\n";
+  StartAndEndSpans();
+  std::this_thread::sleep_for(std::chrono::milliseconds(3000 + 50));
+  std::cout << "....Exported!\n\n\n";
+
+  // Shutdown and drain queue
+  StartAndEndSpans();
+  printf("Shutting down and draining queue.... \n");
+  std::this_thread::sleep_for(std::chrono::milliseconds(2000));
+  // We immediately let the program terminate which invokes the processor destructor
+  // which in turn invokes the processor Shutdown(), which finally drains the queue of ALL
+  // its spans.
+}

examples/simple/CMakeLists.txt

@@ -1 +1,9 @@
+include_directories(${CMAKE_SOURCE_DIR}/exporters/ostream/include)
 
+add_library(foo_library foo_library/foo_library.cc)
+target_link_libraries(foo_library opentelemetry_exporter_ostream_span
+                      ${CMAKE_THREAD_LIBS_INIT} opentelemetry_api)
+
+add_executable(example_simple main.cc)
+target_link_libraries(example_simple ${CMAKE_THREAD_LIBS_INIT} foo_library
+                      opentelemetry_trace)