[svn-r5550] Purpose:

    Code Improvement

Description:
    Split the metadata accumulator code into two parts: one for allowing writes
    of the accumulator buffer during reads (when the buffer is dirty and needs
    to be flushed to disk in order to hold the new metadata being read in) and
    another for only allowing writes of the buffer during writes.

    This allows the MPI-I/O VFL driver to use the metadata accumulator (but
    only during writes) and benefit from the reduced number of metadata I/O
    operations that it brings.

Platforms tested:
    IRIX64 6.5 (modi4) w/parallel

1 files changed, 11 insertions, 3 deletions

diff --git a/src/H5FDpublic.h b/src/H5FDpublic.h
index 49c89bc..52a8dec 100644
--- a/src/H5FDpublic.h
+++ b/src/H5FDpublic.h
@@ -90,8 +90,16 @@ typedef enum H5FD_mem_t {
      * the library will attempt to cache metadata as it is written to the file
      * and build up a larger block of metadata to eventually pass to the VFL
      * 'write' routine.
+     * 
+     * Distinguish between updating the metadata accumulator on writes and
+     * reads.  This is particularly (perhaps only, even) important for MPI-I/O
+     * where we guarantee that writes are collective, but reads may not be.
+     * If we were to allow the metadata accumulator to be written during a
+     * read operation, the application would hang.
      */
-#define H5FD_FEAT_ACCUMULATE_METADATA   0x00000002
+#define H5FD_FEAT_ACCUMULATE_METADATA_WRITE     0x00000002
+#define H5FD_FEAT_ACCUMULATE_METADATA_READ      0x00000004
+#define H5FD_FEAT_ACCUMULATE_METADATA   (H5FD_FEAT_ACCUMULATE_METADATA_WRITE|H5FD_FEAT_ACCUMULATE_METADATA_READ)
     /*
      * Defining the H5FD_FEAT_DATA_SIEVE for a VFL driver means that
      * the library will attempt to cache raw data as it is read from/written to
@@ -99,13 +107,13 @@ typedef enum H5FD_mem_t {
      *  http://www.mcs.anl.gov/~thakur/papers/romio-coll.ps.gz
      *  http://www.mcs.anl.gov/~thakur/papers/mpio-high-perf.ps.gz
      */
-#define H5FD_FEAT_DATA_SIEVE            0x00000004
+#define H5FD_FEAT_DATA_SIEVE            0x00000008
     /*
      * Defining the H5FD_FEAT_AGGREGATE_SMALLDATA for a VFL driver means that
      * the library will attempt to allocate a larger block for "small" raw data
      * and then sub-allocate "small" raw data requests from that larger block.
      */
-#define H5FD_FEAT_AGGREGATE_SMALLDATA   0x00000008
+#define H5FD_FEAT_AGGREGATE_SMALLDATA   0x00000010
 	
 
 /* Forward declaration */