Add check for actually using the MPI file driver when caching one chunk

Better explain rationale behind chunk caching issue fix

1 files changed, 15 insertions, 1 deletions

diff --git a/src/H5Dchunk.c b/src/H5Dchunk.c
index d1528eb..f901cdf 100644
--- a/src/H5Dchunk.c
+++ b/src/H5Dchunk.c
@@ -2943,9 +2943,23 @@ H5D__chunk_lookup(const H5D_t *dset, const hsize_t *scaled,
              * address in the file and/or gets re-allocated with a different size).
              * If we were to cache this information, subsequent reads/writes would
              * retrieve the invalid information and cause a variety of issues.
+             *
+             * This is an ugly and potentially frail check, but the
+             * H5D__chunk_cinfo_cache_reset() function is not currently available
+             * to functions outside of this file, so outside functions can not
+             * invalidate this single chunk cache. Even if the function were available,
+             * this check prevents us from doing the work of going through and caching
+             * each chunk in the write operation, when we're only going to invalidate
+             * the cache at the end of a parallel write anyway.
+             *
+             *  - JTH
              */
 #ifdef H5_HAVE_PARALLEL
-            if ( !((H5F_INTENT(dset->oloc.file) & H5F_ACC_RDWR) && dset->shared->dcpl_cache.pline.nused) )
+            if ( !(    (H5F_HAS_FEATURE(idx_info.f, H5FD_FEAT_HAS_MPI))
+                    && (H5F_INTENT(dset->oloc.file) & H5F_ACC_RDWR)
+                    && dset->shared->dcpl_cache.pline.nused
+                  )
+               )
 #endif
                 H5D__chunk_cinfo_cache_update(&dset->shared->cache.chunk.last, udata);
         } /* end if */