use reductions to account for skew across ranks in start and end time

git-svn-id: https://svn.mcs.anl.gov/repos/darshan/trunk@899 3b7491f3-a168-0410-bf4b-c445ed680a29

ChangeLog

@@ -6,6 +6,9 @@ darshan-2.3.1-pre1
 =============
 * Change OPEN_TIMESTAMP field to report timestamp right before open() is
   invoked rather than after timestamp after open is completed
+* Change start_time and end_time fields in job record to use min and max
+  (respectively) across all ranks
+TODO: bump log version number and add warnings about semantic changes  
 
 darshan-2.3.0
 =============

darshan-runtime/lib/darshan-mpi-io.c

@@ -298,6 +298,8 @@ void darshan_shutdown(int timing_flag)
     char* env_tok;
 #endif
     uint64_t hlevel;
+    int64_t first_start_time;
+    int64_t last_end_time;
 
     CP_LOCK();
     if(!darshan_global_job)
@@ -528,6 +530,17 @@ void darshan_shutdown(int timing_flag)
 
     final_job->log_job.end_time = time(NULL);
 
+    /* reduce to report first start time and last end time across all ranks
+     * at rank 0
+     */
+    DARSHAN_MPI_CALL(PMPI_Reduce)(&final_job->log_job.start_time, &first_start_time, 1, MPI_LONG_LONG, MPI_MIN, 0, MPI_COMM_WORLD); 
+    DARSHAN_MPI_CALL(PMPI_Reduce)(&final_job->log_job.end_time, &last_end_time, 1, MPI_LONG_LONG, MPI_MAX, 0, MPI_COMM_WORLD); 
+    if(rank == 0)
+    {
+        final_job->log_job.start_time = first_start_time;
+        final_job->log_job.end_time = last_end_time;
+    }
+
     /* reduce records for shared files */
     if(timing_flag)
         red1 = DARSHAN_MPI_CALL(PMPI_Wtime)();