Add output_multiplex.

This allows an arbitrary number of output_formats to be wrapped up
into a single object. This output format just forwards all calls to its
children.

nvbench/CMakeLists.txt

@@ -13,6 +13,7 @@ set(srcs
   markdown_format.cu
   named_values.cu
   option_parser.cu
+  output_multiplex.cu
   runner.cu
   state.cu
   string_axis.cu

nvbench/output_multiplex.cu

@@ -0,0 +1,53 @@
+#include <nvbench/output_multiplex.cuh>
+
+#include <iostream>
+
+namespace nvbench
+{
+
+output_multiplex::output_multiplex()
+    : output_format(std::cerr) // Nothing should write to this.
+{}
+
+void output_multiplex::do_print_device_info()
+{
+  for (auto &format_ptr : m_formats)
+  {
+    format_ptr->print_device_info();
+  }
+}
+
+void output_multiplex::do_print_log_preamble()
+{
+  for (auto &format_ptr : m_formats)
+  {
+    format_ptr->print_log_preamble();
+  }
+}
+
+void output_multiplex::do_print_log_epilogue()
+{
+  for (auto &format_ptr : m_formats)
+  {
+    format_ptr->print_log_epilogue();
+  }
+}
+
+void output_multiplex::do_print_benchmark_list(const benchmark_vector &benches)
+{
+  for (auto &format_ptr : m_formats)
+  {
+    format_ptr->print_benchmark_list(benches);
+  }
+}
+
+void output_multiplex::do_print_benchmark_results(
+  const benchmark_vector &benches)
+{
+  for (auto &format_ptr : m_formats)
+  {
+    format_ptr->print_benchmark_results(benches);
+  }
+}
+
+} // namespace nvbench

nvbench/output_multiplex.cuh

@@ -0,0 +1,36 @@
+#pragma once
+
+#include <nvbench/output_format.cuh>
+
+#include <memory>
+#include <vector>
+
+namespace nvbench
+{
+
+/*!
+ * An nvbench::output_format that just forwards calls to other `output_format`s.
+ */
+struct output_multiplex : nvbench::output_format
+{
+
+  output_multiplex();
+
+  template <typename Format, typename... Ts>
+  Format &emplace(Ts &&...ts)
+  {
+    m_formats.push_back(std::make_unique<Format>(std::forward<Ts>(ts)...));
+    return static_cast<Format &>(*m_formats.back());
+  }
+
+private:
+  void do_print_device_info();
+  void do_print_log_preamble();
+  void do_print_log_epilogue();
+  void do_print_benchmark_list(const benchmark_vector &benches);
+  void do_print_benchmark_results(const benchmark_vector &benches);
+
+  std::vector<std::unique_ptr<nvbench::output_format>> m_formats;
+};
+
+} // namespace nvbench