From 8d9ff9aebefe01d52748cc1e5280dc01c0e3c3f6 Mon Sep 17 00:00:00 2001
From: arnav-singhal <43693924+arnav-singhal@users.noreply.github.com>
Date: Mon, 8 Jul 2024 16:40:42 -0700
Subject: [PATCH] HDF5: Correctly determine max_mfi_count (#4024)

## Summary
Fixes a bug so that all processes correctly evaluate the maximum number
of mfi's across all processes, rather than just the preceding ones. This
resulted in lower-number ranks sometimes finishing the write early and
not correctly doing enough dummy writes to write collectively, causing a
crash.

Sorry, I just figured this out this afternoon, after previous pull was
merged.

## Checklist

The proposed changes:
- [X] fix a bug or incorrect behavior in AMReX
- [ ] add new capabilities to AMReX
- [ ] changes answers in the test suite to more than roundoff level
- [ ] are likely to significantly affect the results of downstream AMReX
users
- [ ] include documentation in the code and/or rst files, if appropriate
---
 Src/Extern/HDF5/AMReX_ParticleHDF5.H | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Src/Extern/HDF5/AMReX_ParticleHDF5.H b/Src/Extern/HDF5/AMReX_ParticleHDF5.H
index 00179409616..85f06b63093 100644
--- a/Src/Extern/HDF5/AMReX_ParticleHDF5.H
+++ b/Src/Extern/HDF5/AMReX_ParticleHDF5.H
@@ -842,7 +842,7 @@ ParticleContainer_impl<ParticleType, NArrayReal, NArrayInt, Allocator, CellAssig
     my_real_count  = 0;
 
     int max_mfi_count = 0, write_count = 0;
-    for (int i = 0; i < ParallelDescriptor::MyProc(); i++) {
+    for (int i = 0; i < ParallelDescriptor::NProcs(); i++) {
         if (max_mfi_count < all_mfi_cnt[i]) {
             max_mfi_count = all_mfi_cnt[i];
         }