Add new gather function for std::chrono::milliseconds.

Author: breyerml

include/plssvm/mpi/communicator.hpp

@@ -21,6 +21,7 @@
     #include "mpi.h"  // MPI_Comm, MPI_COMM_WORLD, MPI_Gather
 #endif
 
+#include <chrono>      // std::chrono::milliseconds
 #include <cstddef>     // std::size_t
 #include <functional>  // std::invoke
 #include <string>      // std::string
@@ -126,6 +127,14 @@ class communicator {
      */
     [[nodiscard]] std::vector<std::string> gather(const std::string &str) const;
 
+    /**
+     * @brief Gather the `std::chrono::milliseconds` @p duration from each MPI rank on the `communicator::main_rank()`.
+     * @details If `PLSSVM_HAS_MPI_ENABLED` is undefined, returns the provided @p duration wrapped in a `std::vector`.
+     * @param[in] duration the duration to gather at the main MPI rank
+     * @return a `std::vector` containing all gathered durations (`[[nodiscard]]`)
+     */
+    [[nodiscard]] std::vector<std::chrono::milliseconds> gather(const std::chrono::milliseconds &duration) const;
+
 #if defined(PLSSVM_HAS_MPI_ENABLED)
     /**
      * @brief Add implicit conversion operator back to a native MPI communicator.

src/plssvm/mpi/communicator.cpp

@@ -14,9 +14,12 @@
     #include "mpi.h"
 #endif
 
-#include <cstddef>  // std::size_t
-#include <string>   // std::string
-#include <vector>   // std::vector
+#include <algorithm>  // std::transform
+#include <chrono>     // std::chrono::milliseconds
+#include <cstddef>    // std::size_t
+#include <cstdint>    // std::int64_t
+#include <string>     // std::string
+#include <vector>     // std::vector
 
 namespace plssvm::mpi {
 
@@ -95,4 +98,20 @@ std::vector<std::string> communicator::gather(const std::string &str) const {
 #endif
 }
 
+std::vector<std::chrono::milliseconds> communicator::gather(const std::chrono::milliseconds &duration) const {
+#if defined(PLSSVM_HAS_MPI_ENABLED)
+    // convert the duration to an integer
+    const std::int64_t intermediate_dur = duration.count();
+    std::vector<std::int64_t> intermediate_result(this->size());
+    // gather the integer values from each MPI rank
+    PLSSVM_MPI_ERROR_CHECK(MPI_Gather(&intermediate_dur, 1, detail::mpi_datatype<std::int64_t>(), intermediate_result.data(), 1, detail::mpi_datatype<std::int64_t>(), communicator::main_rank(), comm_));
+    // cast integers back to durations
+    std::vector<std::chrono::milliseconds> result(this->size());
+    std::transform(intermediate_result.cbegin(), intermediate_result.cend(), result.begin(), [](const std::int64_t dur) { return static_cast<std::chrono::milliseconds>(dur); });
+    return result;
+#else
+    return { duration };
+#endif
+}
+
 }  // namespace plssvm::mpi