1 files changed, 10 insertions, 0 deletions
diff --git a/perform/pio_engine.c b/perform/pio_engine.c
index d1ea6d3..efcfa98 100644
--- a/perform/pio_engine.c
+++ b/perform/pio_engine.c
@@ -926,6 +926,16 @@ do_fopen(iotype iot, char *fname, file_descr *fd /*out*/, int flags)
         else
             fd->rawfd = RAWOPEN(fname, O_RDONLY);
 
+        /* The perils of raw I/O in a parallel environment. The problem is:
+         *
+         *      - Process n opens a file with truncation and then starts
+         *        writing to the file.
+         *      - Process m also opens the file with truncation, but after
+         *        process n has already started to write to the file. Thus,
+         *        all of the stuff process n wrote is now lost.
+         */
+        MPI_Barrier(pio_comm_g);
+
         if (fd->rawfd < 0 ) {
             fprintf(stderr, "Raw File Open failed(%s)\n", fname);
             GOTOERROR(FAIL);