From d985c7dee1fc0f19f74cb5f4505be3e1dc47a905 Mon Sep 17 00:00:00 2001
From: Mikael Simberg <simbergm@cscs.ch>
Date: Fri, 24 May 2024 16:00:28 +0200
Subject: [PATCH 1/3] Don't print pool and thread numbers in hexadecimal in
 logs

---
 libs/pika/init_runtime/src/init_logging.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libs/pika/init_runtime/src/init_logging.cpp b/libs/pika/init_runtime/src/init_logging.cpp
index 3a315caac..497f0f750 100644
--- a/libs/pika/init_runtime/src/init_logging.cpp
+++ b/libs/pika/init_runtime/src/init_logging.cpp
@@ -76,7 +76,7 @@ namespace pika::detail {
     {
         static void format_id(spdlog::memory_buf_t& dest, std::size_t i)
         {
-            if (i != std::size_t(-1)) { dest.append(fmt::format("{:04x}", i)); }
+            if (i != std::size_t(-1)) { dest.append(fmt::format("{:04}", i)); }
             else { dest.append(std::string_view("----")); }
         }
 

From 36c5729b77c2c84f3ea5db0fcede17420ad32fc0 Mon Sep 17 00:00:00 2001
From: Mikael Simberg <simbergm@cscs.ch>
Date: Fri, 24 May 2024 16:01:18 +0200
Subject: [PATCH 2/3] Try to get MPI rank in logs with MPI_Comm_rank before
 guessing with environment variables

---
 libs/pika/init_runtime/CMakeLists.txt       |  5 ++++
 libs/pika/init_runtime/src/init_logging.cpp | 28 ++++++++++++++++-----
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/libs/pika/init_runtime/CMakeLists.txt b/libs/pika/init_runtime/CMakeLists.txt
index b2a797fb8..026fec1a8 100644
--- a/libs/pika/init_runtime/CMakeLists.txt
+++ b/libs/pika/init_runtime/CMakeLists.txt
@@ -15,6 +15,10 @@ set(init_runtime_headers
 
 set(init_runtime_sources init_logging.cpp init_runtime.cpp scoped_finalize.cpp)
 
+if(PIKA_WITH_MPI)
+  list(APPEND init_runtime_additional_module_dependencies pika_mpi_base)
+endif()
+
 include(pika_add_module)
 pika_add_module(
   pika init_runtime
@@ -33,5 +37,6 @@ pika_add_module(
     pika_schedulers
     pika_threading_base
     pika_timing
+    ${init_runtime_additional_module_dependencies}
   CMAKE_SUBDIRS examples tests
 )
diff --git a/libs/pika/init_runtime/src/init_logging.cpp b/libs/pika/init_runtime/src/init_logging.cpp
index 497f0f750..3cb864d5d 100644
--- a/libs/pika/init_runtime/src/init_logging.cpp
+++ b/libs/pika/init_runtime/src/init_logging.cpp
@@ -15,6 +15,10 @@
 #include <pika/string_util/from_string.hpp>
 #include <pika/threading_base/thread_data.hpp>
 
+#if defined(PIKA_HAVE_MPI)
+# include <pika/mpi_base/mpi.hpp>
+#endif
+
 #include <fmt/format.h>
 #include <fmt/ostream.h>
 #include <spdlog/pattern_formatter.h>
@@ -105,13 +109,25 @@ namespace pika::detail {
         {
             static PIKA_DETAIL_NS_DEBUG::hostname_print_helper helper{};
             static std::string_view hostname_str = helper.get_hostname();
-            dest.append(hostname_str);
 
-            if (int rank = helper.guess_rank(); rank != -1)
-            {
-                dest.append(hostname_str);
-                dest.append(fmt::format("/{}", rank));
-            }
+            if (!hostname_str.empty()) { dest.append(hostname_str); }
+            else { dest.append(std::string_view("----")); }
+
+            static int rank = [&] {
+            // First try to get the rank through MPI
+#if defined(PIKA_HAVE_MPI)
+                int mpi_initialized = 0;
+                if (MPI_Initialized(&mpi_initialized) == MPI_SUCCESS && mpi_initialized)
+                {
+                    int rank = 0;
+                    if (MPI_Comm_rank(MPI_COMM_WORLD, &rank) == MPI_SUCCESS) { return rank; }
+                }
+#endif
+
+                // Otherwise guess based on environment variables
+                return helper.guess_rank();
+            }();
+            if (rank != -1) { dest.append(fmt::format("/{}", rank)); }
             else { dest.append(std::string_view("/----")); }
         }
 

From 2b845945347ef9fa82b29dfab9f2940ff74cbfca Mon Sep 17 00:00:00 2001
From: Mikael Simberg <simbergm@cscs.ch>
Date: Fri, 24 May 2024 16:01:31 +0200
Subject: [PATCH 3/3] Guess MPI rank from environment variables differently

- Change loop order so that environment variable suffixes are tested in
  order against all environment variables. This reordering means that
  the suffixes are given a priority, instead of the previous order which
  gave priority to the first environment variable matching any of the
  suffixes.
- Change the list of suffixes to be more likely to match the world rank,
  rather than a node id or a local rank.
---
 libs/pika/debugging/src/print.cpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/libs/pika/debugging/src/print.cpp b/libs/pika/debugging/src/print.cpp
index 4e8cabd9f..d7d3f2a07 100644
--- a/libs/pika/debugging/src/print.cpp
+++ b/libs/pika/debugging/src/print.cpp
@@ -273,12 +273,13 @@ namespace PIKA_DETAIL_NS_DEBUG {
 #else
         char** env = environ;
 #endif
-        std::vector<std::string> env_strings{"_RANK=", "_NODEID="};
-        for (char** current = env; *current; current++)
+        std::vector<std::string_view> env_strings{"_PROCID=", "_WORLD_RANK=", "_RANK="};
+
+        for (auto s : env_strings)
         {
-            auto e = std::string(*current);
-            for (auto s : env_strings)
+            for (char** current = env; *current; current++)
             {
+                auto e = std::string(*current);
                 auto pos = e.find(s);
                 if (pos != std::string::npos)
                 {