interim checkin of VFD SWMR writer EOT code.

Added code supporting first cut at the writer end of tick operations.
Tested (to the extent possible) on charis and jelly.

6 files changed, 600 insertions, 100 deletions

diff --git a/src/H5Fint.c b/src/H5Fint.c
index d7ba880..658f1aa 100644
--- a/src/H5Fint.c
+++ b/src/H5Fint.c
@@ -126,6 +126,8 @@ static herr_t H5F__vfd_swmr_construct_write_md_hdr(H5F_t *f, uint32_t num_entrie
 static herr_t H5F__vfd_swmr_construct_write_md_idx(H5F_t *f, uint32_t num_entries, struct H5FD_vfd_swmr_idx_entry_t index[]);
 static herr_t H5F__idx_entry_cmp(const void *_entry1, const void *_entry2);
 static herr_t H5F__vfd_swmr_writer__create_index(H5F_t * f);
+static herr_t H5F_vfd_swmr_writer__prep_for_flush_or_close(H5F_t *f);
+static herr_t H5F__vfd_swmr_writer__wait_a_tick(H5F_t *f);
 
 
 
@@ -138,7 +140,11 @@ H5F_t *vfd_swmr_file_g = NULL;          /* Points to the file struct */
 hbool_t vfd_swmr_g = FALSE;             /* Is this a VFD SWMR configured file */
 hbool_t vfd_swmr_writer_g = FALSE;      /* Is this the VFD SWMR writer */
 uint64_t tick_num_g = 0;                /* The current tick_num */
+#if 1 /* clock_gettime() version */ /* JRM */
 struct timespec end_of_tick_g;          /* The current end_of_tick */
+#else /* gettimeofday() version */ /* JRM */
+struct timeval end_of_tick_g;          /* The current end_of_tick */
+#endif /* gettimeofday() version */ /* JRM */
 
 
 /*****************************/
@@ -1101,11 +1107,18 @@ H5F__new(H5F_file_t *shared, unsigned flags, hid_t fcpl_id, hid_t fapl_id, H5FD_
             HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, NULL, "can't get VFD SWMR config info")
 
         /* Initialization for VFD SWMR */
-        f->shared->vfd_swmr_md_fd = -1;
-        f->shared->fs_man_md = NULL;
-        f->shared->dl_head_ptr = NULL;
-        f->shared->dl_tail_ptr = NULL;
-        f->shared->dl_len = 0;
+        f->shared->vfd_swmr             = FALSE;
+        f->shared->vfd_swmr_writer      = FALSE;
+        f->shared->tick_num             = 0;
+        f->shared->mdf_idx              = NULL;
+        f->shared->mdf_idx_len          = 0;
+        f->shared->mdf_idx_entries_used = 0;
+
+        f->shared->vfd_swmr_md_fd       = -1;
+        f->shared->fs_man_md            = NULL;
+        f->shared->dl_head_ptr          = NULL;
+        f->shared->dl_tail_ptr          = NULL;
+        f->shared->dl_len               = 0;
 
         /* Create a metadata cache with the specified number of elements.
          * The cache might be created with a different number of elements and
@@ -1326,6 +1339,12 @@ H5F__dest(H5F_t *f, hbool_t flush)
             /* Push error, but keep going*/
             HDONE_ERROR(H5E_FILE, H5E_CANTRELEASE, FAIL, "problems closing file")
 
+        /* If this is a VFD SWMR writer, prep for flush or close */
+        if((f->shared->vfd_swmr) && (f->shared->vfd_swmr_writer) &&
+           (H5F_vfd_swmr_writer__prep_for_flush_or_close(f) < 0))
+            /* Push error, but keep going*/
+            HDONE_ERROR(H5E_IO, H5E_CANTFLUSH, FAIL, "vfd swmr prep for flush or close failed")
+
         /* Shutdown the page buffer cache */
         if(H5PB_dest(f) < 0)
             /* Push error, but keep going*/
@@ -1955,6 +1974,12 @@ H5F__flush_phase2(H5F_t *f, hbool_t closing)
         /* Push error, but keep going*/
         HDONE_ERROR(H5E_IO, H5E_CANTFLUSH, FAIL, "unable to flush metadata accumulator")
 
+    /* If this is a VFD SWMR writer, prep for flush or close */
+    if((f->shared->vfd_swmr) && (f->shared->vfd_swmr_writer) &&
+       (H5F_vfd_swmr_writer__prep_for_flush_or_close(f) < 0))
+        /* Push error, but keep going*/
+        HDONE_ERROR(H5E_IO, H5E_CANTFLUSH, FAIL, "vfd swmr prep for flush or close failed")
+
     /* Flush the page buffer */
     if(H5PB_flush(f) < 0)
         /* Push error, but keep going*/
@@ -2039,6 +2064,7 @@ H5F__close(hid_t file_id)
 
         if((nref = H5I_get_ref(file_id, FALSE)) < 0)
             HGOTO_ERROR(H5E_FILE, H5E_CANTGET, FAIL, "can't get ID ref count")
+
         if(nref == 1)
             if(H5F__flush(f) < 0)
                 HGOTO_ERROR(H5E_FILE, H5E_CANTFLUSH, FAIL, "unable to flush cache")
@@ -3606,7 +3632,7 @@ done:
  *              For VFD SWMR writer:
  *
  *                  --set vfd_swmr_writer_g to TRUE
- *                  --set tick_num_g to 0
+ *                  --set tick_num_g to 1
  *                  --create the metadata file
  *                  --when opening an existing HDF5 file, write header and 
  *                    empty index in the metadata file
@@ -3644,7 +3670,12 @@ H5F__vfd_swmr_init(H5F_t *f, hbool_t file_create)
         HDassert(f->shared->vfd_swmr_config.vfd_swmr_writer);
 
         vfd_swmr_writer_g = f->shared->vfd_swmr_writer = TRUE;
-        tick_num_g = f->shared->tick_num = 0;
+        tick_num_g = f->shared->tick_num = 1;
+
+        if ( H5PB_vfd_swmr__set_tick(f) < 0 )
+
+            HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, \
+                        "Can't update page buffer current tick")
 
         /* Create the metadata file */
         if ( ((f->shared->vfd_swmr_md_fd = 
@@ -3907,6 +3938,7 @@ done:
  *
  *-------------------------------------------------------------------------
  */
+#if 1 /* clock_gettime() version */ /* JRM */
 static herr_t
 H5F__vfd_swmr_update_end_of_tick_and_tick_num(H5F_t *f, hbool_t incr_tick_num)
 {
@@ -3954,6 +3986,11 @@ H5F__vfd_swmr_update_end_of_tick_and_tick_num(H5F_t *f, hbool_t incr_tick_num)
         tick_num_g++;
 #endif /* JRM */
         f->shared->tick_num = tick_num_g;
+
+        if ( H5PB_vfd_swmr__set_tick(f) < 0 )
+
+            HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, \
+                        "Can't update page buffer current tick")
     }
 
     /* 
@@ -3982,6 +4019,72 @@ done:
 
 } /* H5F__vfd_swmr_update_end_of_tick_and_tick_num() */
 
+#else /* gettimeofday() version */ /* JRM */
+
+static herr_t
+H5F__vfd_swmr_update_end_of_tick_and_tick_num(H5F_t *f, hbool_t incr_tick_num)
+{
+    struct timeval curr;                /* Current time in struct timeval */
+    struct timeval new_end_of_tick;     /* new end_of_tick in struct timeval */
+    uint64_t tlen_usecs;
+    uint64_t new_usecs;
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    /* Get current time in struct timespec */
+    if ( HDgettimeofday(&curr, NULL) < 0 )
+
+        HGOTO_ERROR(H5E_FILE, H5E_CANTGET, FAIL, \
+                    "can't get time via gettimeofday()")
+
+    /* Convert tick_len to u_secs */
+    tlen_usecs = f->shared->vfd_swmr_config.tick_len * TENTH_SEC_TO_MICROSECS;
+
+    /* compute new end of tick */
+    new_end_of_tick.tv_sec = curr.tv_sec;
+    new_usecs = curr.tv_usec + tlen_usecs;
+
+    while ( new_usecs > SECOND_TO_MICROSECS ) {
+
+        (new_end_of_tick.tv_sec)++;
+        new_usecs -= SECOND_TO_MICROSECS;
+    }
+
+    new_end_of_tick.tv_usec = (suseconds_t)new_usecs;
+
+    /* Update end_of_tick_g, f->shared->end_of_tick */
+
+    HDmemcpy(&end_of_tick_g, &new_end_of_tick, sizeof(struct timeval));
+    HDmemcpy(&f->shared->end_of_tick, &new_end_of_tick, sizeof(struct timeval));
+
+    /* 
+     *  Update tick_num_g, f->shared->tick_num 
+     */
+    if ( incr_tick_num ) {
+
+        /* Regardless of elapsed time, only increment the tick num by 1
+         * so as to avoid the possibility of using up all of max_lag in
+         * one or two ticks.
+         */
+        tick_num_g++;
+
+        f->shared->tick_num = tick_num_g;
+
+        if ( H5PB_vfd_swmr__set_tick(f) < 0 )
+
+            HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, \
+                        "Can't update page buffer current tick")
+    }
+
+done:
+
+    FUNC_LEAVE_NOAPI(ret_value)
+
+} /* H5F__vfd_swmr_update_end_of_tick_and_tick_num() */
+
+#endif /* gettimeofday() version */ /* JRM */
+
 
 /*-------------------------------------------------------------------------
  *
@@ -4319,7 +4422,7 @@ done:
  *           the metadata file index, failure to delay such writes can 
  *           result in message from the future bugs.
  *
- *           The easy case case is pages or multi-page metadata entries
+ *           The easy case is pages or multi-page metadata entries
  *           have just been allocated.  Obviously, these can be written 
  *           immediately.  This case is tracked and tested by the page 
  *           buffer proper.
@@ -4363,7 +4466,7 @@ H5F_vfd_swmr_writer__delay_write(H5F_t *f, uint64_t page,
 
     idx = f->shared->mdf_idx;
 
-    HDassert((idx) ||( f->shared->tick_num <= 0));
+    HDassert((idx) ||( f->shared->tick_num <= 1));
 
     /* do a binary search on the metadata file index to see if
      * it already contains an entry for *pbe_ptr.
@@ -4431,6 +4534,134 @@ done:
 
 /*-------------------------------------------------------------------------
  *
+ * Function: H5F_vfd_swmr_writer__prep_for_flush_or_close
+ *
+ * Purpose:  In the context of the VFD SWMR writer, two issues must be 
+ *           addressed before the page buffer can be flushed -- as is 
+ *           necessary on both HDF5 file flush or close:
+ *
+ *           1) We must force an end of tick so as to clean the tick list
+ *              in the page buffer.
+ *              
+ *           2) If the page buffer delayed write list is not empty, we 
+ *              must repeatedly wait a tick and then run the writer end 
+ *              of tick function until the delayed write list drains.
+ *
+ *           This function manages these details.
+ *
+ * Return:   SUCCEED/FAIL
+ *
+ * Programmer: John Mainzer 11/27/18
+ *
+ * Changes:  None.
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5F_vfd_swmr_writer__prep_for_flush_or_close(H5F_t *f)
+{
+    herr_t ret_value = SUCCEED;              /* Return value */
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    HDassert(f);
+    HDassert(f->shared);
+    HDassert(f->shared->vfd_swmr);
+    HDassert(f->shared->vfd_swmr_writer);
+    HDassert(f->shared->pb_ptr);
+
+    /* since we are about to flush the page buffer, force and end of
+     * tick so as to avoid attempts to flush entries on the page buffer 
+     * tick list that were modified during the current tick.
+     */
+    if ( H5F_vfd_swmr_writer_end_of_tick() < 0 )
+
+        HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, \
+                    "H5F_vfd_swmr_writer_end_of_tick() failed.")
+
+    while(f->shared->pb_ptr->dwl_len > 0) {
+
+        if(H5F__vfd_swmr_writer__wait_a_tick(f) < 0)
+
+            HGOTO_ERROR(H5E_FILE, H5E_CANTFLUSH, FAIL, "wait a tick failed.")
+    }
+
+done:
+
+    FUNC_LEAVE_NOAPI(ret_value)
+
+} /* H5F_vfd_swmr_writer__prep_for_flush_or_close() */
+
+
+/*-------------------------------------------------------------------------
+ *
+ * Function: H5F__vfd_swmr_writer__wait_a_tick
+ *
+ * Purpose:  Before a file that has been opened by a VFD SWMR writer,
+ *           all pending delayed writes must be allowed drain.
+ *
+ *           This function facilitates this by sleeping for a tick, and
+ *           the running the writer end of tick function.  
+ *
+ *           It should only be called as part the flush or close operations.
+ *
+ * Return:   SUCCEED/FAIL
+ *
+ * Programmer: John Mainzer 11/23/18
+ *
+ * Changes:  None.
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5F__vfd_swmr_writer__wait_a_tick(H5F_t *f)
+{
+    int result;
+    struct timespec req;
+    struct timespec rem;
+    uint64_t tick_in_nsec;
+    herr_t ret_value = SUCCEED;              /* Return value */
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    HDassert(f);
+    HDassert(f->shared);
+    HDassert(f->shared->vfd_swmr);
+    HDassert(f->shared->vfd_swmr_writer);
+    HDassert((f == vfd_swmr_file_g) ||
+             ((vfd_swmr_file_g) && (f->shared == vfd_swmr_file_g->shared)));
+
+    tick_in_nsec = f->shared->vfd_swmr_config.tick_len * TENTH_SEC_TO_NANOSECS;
+    req.tv_nsec = (long)(tick_in_nsec % SECOND_TO_NANOSECS);
+    req.tv_sec = (time_t)(tick_in_nsec / SECOND_TO_NANOSECS);
+
+    result = HDnanosleep(&req, &rem);
+
+    while ( result == -1 ) {
+
+        req.tv_nsec = rem.tv_nsec;
+        req.tv_sec = rem.tv_sec;
+        result = HDnanosleep(&req, &rem);
+    }
+
+    if ( result != 0 )
+
+        HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, "HDnanosleep() failed.")
+        
+    if ( H5F_vfd_swmr_writer_end_of_tick() < 0 )
+
+        HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, \
+                    "H5F_vfd_swmr_writer_end_of_tick() failed.")
+    
+done:
+
+    FUNC_LEAVE_NOAPI(ret_value)
+
+} /* H5F__vfd_swmr_writer__wait_a_tick() */
+
+
+/*-------------------------------------------------------------------------
+ *
  * Function: H5F_vfd_swmr_writer_end_of_tick
  *
  * Purpose:  Main routine for managing the end of tick for the VFD 
@@ -4445,7 +4676,15 @@ done:
  *
  *            2) Flush the metadata cache to the page buffer.
  *
- *            3) If this is the first tick (i.e. tick == 0), create the
+ *               Note that we must run a tick after the destruction 
+ *               of the metadata cache, since this operation will usually
+ *               dirty the first page in the HDF5 file.  However, the 
+ *               metadata cache will no longer exist at this point.
+ *
+ *               Thus, we must check for the existance of the metadata 
+ *               cache, and only attempt to flush it if it exists.
+ *
+ *            3) If this is the first tick (i.e. tick == 1), create the
  *               in memory version of the metadata file index.
  *
  *            4) Scan the page buffer tick list, and use it to update 
@@ -4459,25 +4698,15 @@ done:
  *
  *               (This is an optimization -- adress it later)
  *
- *            6) Scan the page buffer delayed write list for entries that 
- *               may now be written, and move any such entries to the 
- *               page buffer LRU.
- *
- *               (For the first cut, we will assume file was just created,
- *                that there have been no flushes, and that no entries 
- *                have been removed from the metadata file index.  Under 
- *                these circumstances, the delayed write list must always 
- *                be empty. Thus delay implementing this.)
- *
- *            7) Update the metadata file.  Must do this before we 
+ *            6) Update the metadata file.  Must do this before we 
  *               release the tick list, as otherwise the page buffer 
  *               entry images may not be available.
  *
- *            8) Release the page buffer tick list.
+ *            7) Release the page buffer tick list.
  *
- *            9) Release any delayed writes whose delay has expired.
+ *            8) Release any delayed writes whose delay has expired.
  *
- *           10) Increment the tick, and update the end of tick.
+ *            9) Increment the tick, and update the end of tick.
  *
  *           In passing, generate log entries as appropriate.
  *
@@ -4507,6 +4736,7 @@ H5F_vfd_swmr_writer_end_of_tick(void)
     HDassert(f->shared);
     HDassert(f->shared->pb_ptr);
     HDassert(f->shared->vfd_swmr_writer);
+
   
     /* 1) If requested, flush all raw data to the HDF5 file.
      *
@@ -4518,17 +4748,20 @@ H5F_vfd_swmr_writer_end_of_tick(void)
     }
 
 
-    /* 2) Flush the metadata cache to the page buffer. */
-    if ( H5AC_flush(f) < 0 ) 
+    /* 2) If it exists, flush the metadata cache to the page buffer. */
+    if ( f->shared->cache ) {
+
+        if ( H5AC_flush(f) < 0 ) 
+
+            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
+                        "Can't flush metadata cache to the page buffer")
+    }
 
-        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, \
-                    "Can't flush metadata cache to the page buffer")
- 
 
-    /* 3) If this is the first tick (i.e. tick == 0), create the
+    /* 3) If this is the first tick (i.e. tick == 1), create the
      *    in memory version of the metadata file index.
      */
-    if ( ( f->shared->tick_num == 0 ) &&
+    if ( ( f->shared->tick_num == 1 ) &&
          ( H5F__vfd_swmr_writer__create_index(f) < 0 ) )
 
 
@@ -4553,31 +4786,26 @@ H5F_vfd_swmr_writer_end_of_tick(void)
      */
 
 
-    /* 6) Scan the page buffer delayed write list for entries that 
-     *    may now be written, and move any such entries to the 
-     *    page buffer LRU.
-     *
-     *    (For the first cut, we will assume file was just created,
-     *     that there have been no flushes, and that no entries 
-     *     have been removed from the metadata file index.  Under 
-     *     these circumstances, the delayed write list must always 
-     *     be empty. Thus delay implementing this.)
-     */
-    HDassert( f->shared->pb_ptr->dwl_len == 0 );
-
-
-    /* 7) Update the metadata file.  Must do this before we 
+    /* 6) Update the metadata file.  Must do this before we 
      *    release the tick list, as otherwise the page buffer 
      *    entry images may not be available.
      *
      *    Note that this operation will restore the index to 
      *    sorted order.
      */
-    if ( H5F_update_vfd_swmr_metadata_file(f, 
+    if ( (uint32_t)(f->shared->mdf_idx_entries_used + idx_entries_added) > 0 ) {
+
+        if ( H5F_update_vfd_swmr_metadata_file(f, 
                 (uint32_t)(f->shared->mdf_idx_entries_used + idx_entries_added),
                 f->shared->mdf_idx) < 0 )
 
-        HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, "can't update MD file")
+            HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, "can't update MD file")
+    } else {
+
+        if ( H5F_update_vfd_swmr_metadata_file(f, 0, NULL) < 0 )
+
+            HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, "can't update MD file")
+    }
 
     /* at this point the metadata file index should be sorted -- update
      * f->shared->mdf_idx_entries_used.
@@ -4587,19 +4815,19 @@ H5F_vfd_swmr_writer_end_of_tick(void)
     HDassert(f->shared->mdf_idx_entries_used <= f->shared->mdf_idx_len);
 
 
-    /* 8) Release the page buffer tick list. */
+    /* 7) Release the page buffer tick list. */
     if ( H5PB_vfd_swmr__release_tick_list(f) < 0 )
 
         HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, "can't release tick list")
 
 
-    /* 9) Release any delayed writes whose delay has expired */
+    /* 8) Release any delayed writes whose delay has expired */
     if ( H5PB_vfd_swmr__release_delayed_writes(f) < 0 )
 
         HGOTO_ERROR(H5E_FILE, H5E_SYSTEM, FAIL, "can't release delayed writes")
  
 
-    /* 10) Increment the tick, and update the end of tick. */
+    /* 9) Increment the tick, and update the end of tick. */
     if( vfd_swmr_file_g ) {
 
         /* Update end_of_tick */
diff --git a/src/H5Fpkg.h b/src/H5Fpkg.h
index d725f77..55aae9e 100644
--- a/src/H5Fpkg.h
+++ b/src/H5Fpkg.h
@@ -393,7 +393,11 @@ struct H5F_file_t {
                                              * not 
                                              */
     uint64_t tick_num;                      /* Number of the current tick */
+#if 1 /* use clock_gettime() */ /* JRM */
     struct timespec end_of_tick;            /* End time of the current tick */
+#else /* use gettimeofday() */ /* JRM */
+    struct timeval end_of_tick;             /* End time of the current tick */
+#endif /* use gettimeofday() */ /* JRM */
 
     /* VFD SWMR metadata file index */
     H5FD_vfd_swmr_idx_entry_t * mdf_idx;    /* pointer to an array of instance
diff --git a/src/H5PB.c b/src/H5PB.c
index 62e85d4..d38a5cd 100644
--- a/src/H5PB.c
+++ b/src/H5PB.c
@@ -495,6 +495,7 @@ herr_t
 H5PB_create(H5F_t *f, size_t size, unsigned page_buf_min_meta_perc, 
             unsigned page_buf_min_raw_perc)
 {
+    hbool_t vfd_swmr_writer = FALSE;
     int i;
     int32_t min_md_pages;
     int32_t min_rd_pages;
@@ -545,6 +546,14 @@ H5PB_create(H5F_t *f, size_t size, unsigned page_buf_min_meta_perc,
              (int32_t)(size / f->shared->fs_page_size));
 
 
+    /* compute vfd_swmr_writer */
+    if ( ( H5F_VFD_SWMR_CONFIG(f) ) && ( H5F_INTENT(f) & H5F_ACC_RDWR ) ) {
+
+        HDassert(f->shared->vfd_swmr_config.vfd_swmr_writer);
+        vfd_swmr_writer = TRUE;
+    }
+
+
     /* Allocate the new page buffering structure */
     if(NULL == (pb_ptr = H5FL_MALLOC(H5PB_t)))
 
@@ -591,7 +600,7 @@ H5PB_create(H5F_t *f, size_t size, unsigned page_buf_min_meta_perc,
     /* VFD SWMR specific fields.  
      * The following fields are defined iff vfd_swmr_writer is TRUE. 
      */
-    pb_ptr->vfd_swmr_writer  = FALSE;
+    pb_ptr->vfd_swmr_writer  = vfd_swmr_writer;
     pb_ptr->mpmde_count      = 0;
     pb_ptr->cur_tick         = 0;
 
@@ -1097,9 +1106,12 @@ done:
  * Function:    H5PB_remove_entry
  *
  * Purpose:     Remove possible metadata entry with ADDR from the PB cache.
+ *
  *              This is in response to the data corruption bug from fheap.c 
  *              with page buffering + page strategy.
+ *
  *              Note: Large metadata page bypasses the PB cache.
+ *
  *              Note: Update of raw data page (large or small sized) is 
  *                    handled by the PB cache.
  *
@@ -1109,6 +1121,13 @@ done:
  *
  * Changes:     Reworked function for re-implementation of the page buffer.
  *
+ *              In the context of VFD SWMR, it is possible that the 
+ *              discarded page or multi-page metadata entry has been 
+ *              modified during the current tick and/or is subject to a 
+ *              delayed write.  We must detect this, and remove the entry
+ *              from the tick list and/or delayed write list before it is
+ *              evicted.
+ *
  *              Vailin: I think we need to do this for raw data as well.
  *
  *                                               JRM -- 10/23/18
@@ -1145,6 +1164,25 @@ H5PB_remove_entry(const H5F_t *f, haddr_t addr)
         HDassert(entry_ptr->addr == addr);
         HDassert(entry_ptr->size == pb_ptr->page_size);
 
+        if ( entry_ptr->modified_this_tick ) {
+
+            H5PB__REMOVE_FROM_TL(pb_ptr, entry_ptr, FAIL);
+
+            entry_ptr->modified_this_tick = FALSE;
+        }
+
+        if ( entry_ptr->delay_write_until > 0 ) {
+
+            entry_ptr->delay_write_until = 0;
+
+            H5PB__REMOVE_FROM_DWL(pb_ptr, entry_ptr, FAIL)
+
+            if ( ! ( entry_ptr->is_mpmde ) ) {
+
+                H5PB__UPDATE_RP_FOR_INSERTION(pb_ptr, entry_ptr, FAIL);
+            }
+        }
+
         /* if the entry is dirty, mark it clean before we evict */
         if ( ( entry_ptr->is_dirty ) && 
              ( H5PB__mark_entry_clean(pb_ptr, entry_ptr) < 0 ) )
@@ -1156,6 +1194,22 @@ H5PB_remove_entry(const H5F_t *f, haddr_t addr)
 
             HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, "forced eviction failed")
 
+        /* Do we need to remove the entry from the metadata file index in 
+         * the VFD SWMR case?
+         *
+         * Probably yes -- suppose a page is deallocated, and a multipage
+         * metadata entry is allocated at the same base address.  This would
+         * change the metadata file entry size.
+         *
+         * However, this is sufficiently improbably that it doesn't cause
+         * problems (that I know of) at present.  
+         *
+         * Unless it does, hold off on this until we add code to allow entries
+         * to age out of the metadata file index, as that will give us the 
+         * necessary infrastructure.
+         *
+         *                                         JRM -- 12/6/18
+         */
     }
 
 done:
@@ -1312,12 +1366,12 @@ H5PB_vfd_swmr__release_delayed_writes(H5F_t * f)
 
         HDassert(entry_ptr->is_dirty);
 
-        H5PB__REMOVE_FROM_DWL(pb_ptr, entry_ptr, FAIL)
-
         entry_ptr->delay_write_until = 0;
 
-        if ( entry_ptr->is_mpmde ) { /* flush and evict now */
+        H5PB__REMOVE_FROM_DWL(pb_ptr, entry_ptr, FAIL)
 
+        if ( entry_ptr->is_mpmde ) { /* flush and evict now */
+            
             if ( H5PB__flush_entry(f, pb_ptr, entry_ptr) < 0 )
 
                 HGOTO_ERROR(H5E_PAGEBUF, H5E_WRITEERROR, FAIL, \
@@ -1429,6 +1483,59 @@ done:
 
 /*-------------------------------------------------------------------------
  *
+ * Function:	H5PB_vfd_swmr__set_tick
+ *
+ * Purpose:	At the beginning of each tick, the page buffer must be told
+ *              to synchronize its copy of the current tick with that of 
+ *              the file to which the page buffer belongs.
+ *
+ *              This function performs this function.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	John Mainzer -- 11/20/18
+ *
+ * Changes:     None.
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t 
+H5PB_vfd_swmr__set_tick(H5F_t * f)
+{
+    H5PB_t * pb_ptr = NULL;
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    /* Sanity checks */
+    HDassert(f);
+    HDassert(f->shared);
+    HDassert(f->shared->vfd_swmr);
+    HDassert(f->shared->vfd_swmr_writer);
+
+    pb_ptr = f->shared->pb_ptr;
+
+    HDassert(pb_ptr);
+    HDassert(pb_ptr->magic == H5PB__H5PB_T_MAGIC);
+    HDassert(pb_ptr->vfd_swmr_writer);
+
+    /* the tick must always increase by 1 -- verify this */
+    if ( f->shared->tick_num != pb_ptr->cur_tick + 1 )
+
+        HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
+                    "f->shared->tick_num != pb_ptr->cur_tick + 1 ?!?!")
+
+    pb_ptr->cur_tick = f->shared->tick_num;
+
+done:
+
+    FUNC_LEAVE_NOAPI(ret_value)
+
+} /* H5PB_vfd_swmr__release_tick_list */
+
+
+/*-------------------------------------------------------------------------
+ *
  * Function:	H5PB_vfd_swmr__update_index
  *
  * Purpose:	In the VFD SWMR writer, all metadata writes to the page 
@@ -1611,7 +1718,8 @@ H5PB_vfd_swmr__update_index(H5F_t * f,
 
             if ( new_index_entry_index >= f->shared->mdf_idx_len ) {
 
-                HDfprintf(stderr, "\n\nmax mdf index len exceeded.\n\n");
+                HDfprintf(stderr, "\n\nmax mdf index len (%d)exceeded.\n\n",
+                          f->shared->mdf_idx_len);
                 exit(1);
             }
 
@@ -1648,6 +1756,8 @@ H5PB_vfd_swmr__update_index(H5F_t * f,
         }
 
         HDassert(ie_ptr);
+
+        pbe_ptr = pbe_ptr->tl_next;
     }
 
     /* scan the metadata file index for entries that don't appear in the 
@@ -2060,16 +2170,19 @@ H5PB__create_new_page(H5PB_t *pb_ptr, haddr_t addr, size_t size,
     entry_ptr->mem_type    = type;
     entry_ptr->is_metadata = (type != H5FD_MEM_DRAW);
     entry_ptr->is_mpmde    = ((entry_ptr->is_metadata) &&
-                                  (size > pb_ptr->page_size));
+                              (size > pb_ptr->page_size));
     entry_ptr->is_dirty    = FALSE;
 
     /* insert in the hash table */
     H5PB__INSERT_IN_INDEX(pb_ptr, entry_ptr, FAIL)
     inserted_in_index = TRUE; 
 
-    /* insert at the head of the LRU */
-    H5PB__UPDATE_RP_FOR_INSERTION(pb_ptr, entry_ptr, FAIL)
-    inserted_in_lru = TRUE;
+    /* insert at the head of the LRU if it isn't a multi-page metadata entry */
+    if ( ! entry_ptr->is_mpmde ) {
+
+        H5PB__UPDATE_RP_FOR_INSERTION(pb_ptr, entry_ptr, FAIL)
+        inserted_in_lru = TRUE;
+    }
 
     /* updates stats */
     H5PB__UPDATE_STATS_FOR_INSERTION(pb_ptr, entry_ptr);
@@ -2165,6 +2278,13 @@ H5PB__deallocate_page(H5PB_entry_t *entry_ptr)
  *              and error unless the force parameter is TRUE, in which
  *              case, these constraints are igmored.
  *
+ *              In the context of VFD SWMR, there is also the requirement
+ *              that entries to be evicted not be on the tick list, and
+ *              also not reside on the delayed write list.  In the rare
+ *              case in which such a page is discarded by the free space
+ *              manager, it must be removed from the tick list and/or the
+ *              delayed write list before being evicted by this function.
+ *
  * Return:	Non-negative on success/Negative on failure
  *
  * Programmer:	John Mainzer -- 10/14/18
@@ -2229,8 +2349,11 @@ H5PB__evict_entry(H5PB_t *pb_ptr, H5PB_entry_t *entry_ptr, hbool_t force)
         HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, "mark entry clean failed")
     }
 
-    /* remove the entry from the LRU */
-    H5PB__UPDATE_RP_FOR_EVICTION(pb_ptr, entry_ptr, FAIL)
+    /* if the entry is in the replacement policy, remove it */
+    if ( ! (entry_ptr->is_mpmde) ) {
+
+        H5PB__UPDATE_RP_FOR_EVICTION(pb_ptr, entry_ptr, FAIL)
+    }
 
     /* remove the entry from the hash table */
     H5PB__DELETE_FROM_INDEX(pb_ptr, entry_ptr, FAIL)
@@ -2296,7 +2419,7 @@ H5PB__flush_entry(H5F_t *f, H5PB_t *pb_ptr, H5PB_entry_t *entry_ptr)
     HDassert(entry_ptr->image_ptr);
     HDassert(entry_ptr->is_dirty);
     HDassert((pb_ptr->vfd_swmr_writer) || (!(entry_ptr->is_mpmde)));
-    HDassert(0 == (entry_ptr->delay_write_until));
+    HDassert((uint64_t)0 == (entry_ptr->delay_write_until));
 
     /* Retrieve the 'eoa' for the file */
     if ( HADDR_UNDEF == (eoa = H5F_get_eoa(f, entry_ptr->mem_type)) )
@@ -2766,7 +2889,6 @@ done:
 static herr_t
 H5PB__mark_entry_dirty(H5F_t * f, H5PB_t *pb_ptr, H5PB_entry_t *entry_ptr)
 {
-    uint64_t delay_write_until = 0;
     herr_t ret_value = SUCCEED;    /* Return value */
 
     FUNC_ENTER_NOAPI(FAIL)
@@ -2795,12 +2917,19 @@ H5PB__mark_entry_dirty(H5F_t * f, H5PB_t *pb_ptr, H5PB_entry_t *entry_ptr)
         if ( ( pb_ptr->vfd_swmr_writer ) &&
              ( entry_ptr->loaded ) &&
              ( H5F_vfd_swmr_writer__delay_write(f, entry_ptr->page, 
-                                                &delay_write_until) < 0 ) )
+                                        &(entry_ptr->delay_write_until)) < 0 ) )
 
             HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, FAIL, \
                         "get delayed write request failed")
 
-        if ( delay_write_until > 0 ) {
+        if ( entry_ptr->delay_write_until > 0 ) {
+
+            if ( ! ( entry_ptr->is_mpmde ) ) { 
+
+                /* remove the entry from the replacement policy */
+
+                H5PB__UPDATE_RP_FOR_REMOVE(pb_ptr, entry_ptr, FAIL)
+            }
 
             H5PB__INSERT_IN_DWL(pb_ptr, entry_ptr, FAIL)
 
@@ -3635,8 +3764,8 @@ H5PB__write_meta(H5F_t *f, H5FD_mem_t type, haddr_t addr, size_t size,
     HDassert((size <= pb_ptr->page_size) || (addr == page_addr));
 
 
-    /* case 7) metadata read of size greater than page size. */
-    if ( size >= pb_ptr->page_size ) {
+    /* case 7) metadata write of size greater than page size. */
+    if ( size > pb_ptr->page_size ) {
 
         /* The write must be for a multi-page metadata entry, and 
          * we must be running as a VFD SWMR writer.
diff --git a/src/H5PBpkg.h b/src/H5PBpkg.h
index c6d13db..4af81e6 100644
--- a/src/H5PBpkg.h
+++ b/src/H5PBpkg.h
@@ -108,7 +108,7 @@ if ( ( ( ( (head_ptr) == NULL ) || ( (tail_ptr) == NULL ) ) &&            \
        )                                                                  \
      )                                                                    \
    ) {                                                                    \
-    HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, (fv), "DLL sanity check failed")   \
+    HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, (fv), "DLL sanity check failed") \
 }
 
 #define H5PB__DLL_PRE_INSERT_SC(entry_ptr, head_ptr, tail_ptr, len, Size, fv) \
@@ -129,7 +129,8 @@ if ( ( (entry_ptr) == NULL ) ||                                               \
        )                                                                      \
      )                                                                        \
    ) {                                                                        \
-    HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, (fv), "DLL pre insert SC failed")      \
+    HDassert(FALSE); \
+    HGOTO_ERROR(H5E_PAGEBUF, H5E_SYSTEM, (fv), "DLL pre insert SC failed")    \
 }
 
 #else /* H5PB__DO_SANITY_CHECKS */
@@ -310,9 +311,30 @@ if ( ( ( ( (head_ptr) == NULL ) || ( (tail_ptr) == NULL ) ) &&             \
 
 
 #define H5PB__IL_DLL_APPEND(entry_ptr, head_ptr, tail_ptr, len, Size, fail_val)\
-{                                                                             \
+{                                                                              \
     H5PB__IL_DLL_PRE_INSERT_SC(entry_ptr, head_ptr, tail_ptr, len, Size,       \
-                               fail_val)                                      \
+                               fail_val)                                       \
+    if ( (head_ptr) == NULL )                                                  \
+    {                                                                          \
+       (head_ptr) = (entry_ptr);                                               \
+       (tail_ptr) = (entry_ptr);                                               \
+    }                                                                          \
+    else                                                                       \
+    {                                                                          \
+       (tail_ptr)->il_next = (entry_ptr);                                      \
+       (entry_ptr)->il_prev = (tail_ptr);                                      \
+       (tail_ptr) = (entry_ptr);                                               \
+    }                                                                          \
+    (len)++;                                                                   \
+    (Size) += (int64_t)((entry_ptr)->size);                                    \
+    H5PB__IL_DLL_SC(head_ptr, tail_ptr, len, Size, fail_val)                   \
+} /* H5PB__IL_DLL_APPEND() */
+
+#define H5PB__IL_DLL_PREPEND(entry_ptr, head_ptr, tail_ptr, len, Size,        \
+                             fail_val)                                        \
+{                                                                             \
+    H5PB__DLL_PRE_INSERT_SC(entry_ptr, head_ptr, tail_ptr, len, Size,         \
+                            fail_val)                                         \
     if ( (head_ptr) == NULL )                                                 \
     {                                                                         \
        (head_ptr) = (entry_ptr);                                              \
@@ -320,14 +342,45 @@ if ( ( ( ( (head_ptr) == NULL ) || ( (tail_ptr) == NULL ) ) &&             \
     }                                                                         \
     else                                                                      \
     {                                                                         \
-       (tail_ptr)->il_next = (entry_ptr);                                     \
-       (entry_ptr)->il_prev = (tail_ptr);                                     \
-       (tail_ptr) = (entry_ptr);                                              \
+       (head_ptr)->il_prev = (entry_ptr);                                     \
+       (entry_ptr)->il_next = (head_ptr);                                     \
+       (head_ptr) = (entry_ptr);                                              \
     }                                                                         \
     (len)++;                                                                  \
     (Size) += (int64_t)((entry_ptr)->size);                                   \
-    H5PB__IL_DLL_SC(head_ptr, tail_ptr, len, Size, fail_val)                   \
-} /* H5PB__IL_DLL_APPEND() */
+} /* H5PB__DLL_PREPEND() */
+
+
+#define H5PB__IL_DLL_INSERT_BEFORE(entry_ptr, suc_ptr, head_ptr, tail_ptr,    \
+                                   len, Size, fail_val)                       \
+{                                                                             \
+    HDassert( ((suc_ptr) == NULL) ||                                          \
+              ((suc_ptr)->magic == H5PB__H5PB_ENTRY_T_MAGIC) );               \
+                                                                              \
+    if ( suc_ptr == NULL )                                                    \
+        /* list empty or no successor -- append */                            \
+        H5PB__IL_DLL_APPEND(entry_ptr, head_ptr, tail_ptr, len, Size,         \
+                            fail_val)                                         \
+                                                                              \
+    else if ( suc_ptr->il_prev == NULL )                                      \
+        /* successor at head of list -- prepend */                            \
+        H5PB__IL_DLL_PREPEND(entry_ptr, head_ptr, tail_ptr, len, Size,        \
+                             fail_val)                                        \
+                                                                              \
+    else /* sucessor in body of list -- insert before it */                   \
+    {                                                                         \
+        H5PB__IL_DLL_PRE_INSERT_SC(entry_ptr, head_ptr, tail_ptr, len, Size,  \
+                                   fail_val)                                  \
+        HDassert(suc_ptr->il_prev->magic == H5PB__H5PB_ENTRY_T_MAGIC);        \
+        HDassert(suc_ptr->il_prev->il_next == suc_ptr);                       \
+        entry_ptr->il_prev = suc_ptr->il_prev;                                \
+        entry_ptr->il_prev->il_next = entry_ptr;                              \
+        entry_ptr->il_next = suc_ptr;                                         \
+        suc_ptr->il_prev = entry_ptr;                                         \
+        (len)++;                                                              \
+        (Size) += (int64_t)((entry_ptr)->size);                               \
+    }                                                                         \
+} /* H5PB__DLL_INSERT_BEFORE() */
 
 #define H5PB__IL_DLL_REMOVE(entry_ptr, head_ptr, tail_ptr, len, Size, fv)    \
 {                                                                           \
@@ -1295,6 +1348,54 @@ if ( ( (pb_ptr)->index_size !=                                        \
                                                                   \
 } /* H5PB__UPDATE_RP_FOR_EVICTION */
 
+/*-------------------------------------------------------------------------
+ *
+ * Macro:	H5PB__UPDATE_RP_FOR_REMOVE
+ *
+ * Purpose:     Update the replacement policy data structures for the
+ *		removal of the specified page buffer entry from the 
+ *              replacement policy, but not from the page buffer.  
+ *
+ *              At present, this this only happens when an entry is 
+ *              dirtied, and subject to a delayed write.
+ *
+ *		At present, we only support the modified LRU policy, so
+ *		this function deals with that case unconditionally.  If
+ *		we ever support other replacement policies, the function
+ *		should switch on the current policy and act accordingly.
+ *
+ * Return:      Non-negative on success/Negative on failure.
+ *
+ * Programmer:  John Mainzer, 10/09/18
+ *
+ * Modifications:
+ *
+ *		None.
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#define H5PB__UPDATE_RP_FOR_REMOVE(pb_ptr, entry_ptr, fail_val) \
+{                                                               \
+    HDassert( (pb_ptr) );                                       \
+    HDassert( (pb_ptr)->magic == H5PB__H5PB_T_MAGIC );          \
+    HDassert( (entry_ptr) );                                    \
+    HDassert( (entry_ptr)->magic == H5PB__H5PB_ENTRY_T_MAGIC ); \
+    HDassert( ! ((entry_ptr)->is_mpmde) );                      \
+    HDassert( (entry_ptr)->size == pb_ptr->page_size );         \
+                                                                \
+    /* modified LRU specific code */                            \
+                                                                \
+    /* remove the entry from the LRU list. */                   \
+                                                                \
+    H5PB__DLL_REMOVE((entry_ptr), (pb_ptr)->LRU_head_ptr,       \
+                     (pb_ptr)->LRU_tail_ptr, (pb_ptr)->LRU_len, \
+                     (pb_ptr)->LRU_size, (fail_val))            \
+                                                                \
+    /* End modified LRU specific code. */                       \
+                                                                \
+} /* H5PB__UPDATE_RP_FOR_EVICTION */
+
 
 /*-------------------------------------------------------------------------
  *
@@ -1646,7 +1747,8 @@ if ( ( (pb_ptr)->index_size !=                                        \
         suc_ptr = suc_ptr->next;                                              \
     }                                                                         \
                                                                               \
-    H5PB__DLL_INSERT_BEFORE((entry_ptr), (suc_ptr), (pb_ptr)->dwl_head_ptr,   \
+    H5PB__DLL_INSERT_BEFORE((entry_ptr), (suc_ptr),                           \
+                            (pb_ptr)->dwl_head_ptr,                           \
                             (pb_ptr)->dwl_tail_ptr, (pb_ptr)->dwl_len,        \
                             (pb_ptr)->dwl_size, (fail_val))                   \
                                                                               \
@@ -1685,11 +1787,11 @@ if ( ( (pb_ptr)->index_size !=                                        \
     HDassert( (entry_ptr) );                                         \
     HDassert( (entry_ptr)->magic == H5PB__H5PB_ENTRY_T_MAGIC );      \
     HDassert( (entry_ptr)->size >= pb_ptr->page_size );              \
-    HDassert( (entry_ptr)->delay_write_until < (pb_ptr)->cur_tick ); \
+    HDassert( (entry_ptr)->delay_write_until == 0 );                 \
                                                                      \
     /* remove the entry from the delayed write list. */              \
                                                                      \
-    H5PB__TL_DLL_REMOVE((entry_ptr), (pb_ptr)->dwl_head_ptr,         \
+    H5PB__DLL_REMOVE((entry_ptr), (pb_ptr)->dwl_head_ptr,            \
                      (pb_ptr)->dwl_tail_ptr, (pb_ptr)->dwl_len,      \
                      (pb_ptr)->dwl_size, (fail_val))                 \
                                                                      \
diff --git a/src/H5PBprivate.h b/src/H5PBprivate.h
index 7aabcd5..201a298 100644
--- a/src/H5PBprivate.h
+++ b/src/H5PBprivate.h
@@ -694,6 +694,8 @@ H5_DLL herr_t H5PB_vfd_swmr__release_delayed_writes(H5F_t * f);
 
 H5_DLL herr_t H5PB_vfd_swmr__release_tick_list(H5F_t * f);
 
+H5_DLL herr_t H5PB_vfd_swmr__set_tick(H5F_t * f);
+
 H5_DLL herr_t H5PB_vfd_swmr__update_index(H5F_t * f, int * idx_ent_added_ptr,
     int * idx_ent_modified_ptr, int * idx_ent_not_in_tl_ptr,
     int * idx_ent_not_in_tl_flushed_ptr);
diff --git a/src/H5private.h b/src/H5private.h
index fb01d06..b64903b 100644
--- a/src/H5private.h
+++ b/src/H5private.h
@@ -375,8 +375,12 @@
 #  define H5_EXP2(n)    (1 << (n))
 
 /* VFD SWMR */
-#define SECOND_TO_NANOSECS          1000000000      /* Second to nanoseconds */
-#define TENTH_SEC_TO_NANOSECS       100000000       /* Tenth of a second to nanoseconds */
+#define SECOND_TO_NANOSECS          1000000000 /* Second to nanoseconds */
+#define TENTH_SEC_TO_NANOSECS       100000000  /* 0.1 second to nanoseconds */
+#if 0 /* use gettimeofday() */ /* JRM */
+#define SECOND_TO_MICROSECS         1000000    /* Second to microseconds */
+#define TENTH_SEC_TO_MICROSECS      100000     /* 0.1 second to microseconds */
+#endif /* use gettimeofday() */ /* JRM */
 
 /*
  * HDF Boolean type.
@@ -1953,7 +1957,11 @@ extern hbool_t H5_libterm_g;    /* Is the library being shutdown? */
 extern hbool_t vfd_swmr_g;
 extern hbool_t vfd_swmr_writer_g;
 extern uint64_t tick_num_g;
+#if 1 /* use clock_gettime() */ /* JRM */
 extern struct timespec end_of_tick_g;
+#else /* use gettimeofday() */ /* JRM */
+extern struct timeval end_of_tick_g;
+#endif /* use gettimeofday() */ /* JRM */
 
 #endif /* H5_HAVE_THREADSAFE */
 
@@ -2070,26 +2078,53 @@ H5_DLL herr_t H5CX_pop(void);
                                                                               \
     BEGIN_MPE_LOG
 
-#define VFD_SWMR_TEST_FOR_END_OF_TICK(swmr_reader_exit, err)                                            \
-    /* Initialize the library */                                                                        \
-    if(vfd_swmr_g) {                                                                                    \
-        struct timespec curr_time;                                                                      \
-        long curr_nsecs, end_nsecs;                                                                     \
-        if(HDclock_gettime(CLOCK_MONOTONIC, &curr_time) < 0)                                            \
-            HGOTO_ERROR(H5E_FUNC, H5E_CANTGET, err, "can't get time via clock_gettime")                 \
-        curr_nsecs = curr_time.tv_sec * 1000000000 + curr_time.tv_nsec;                                 \
-        end_nsecs = end_of_tick_g.tv_sec * 1000000000 + end_of_tick_g.tv_nsec;                          \
-        if(curr_nsecs > end_nsecs) {                                                                    \
-            if(vfd_swmr_writer_g) {                                                                     \
-                if(H5F_vfd_swmr_writer_end_of_tick() < 0)                                               \
-                    HGOTO_ERROR(H5E_FUNC, H5E_CANTSET, err, "end of tick error for VFD SWMR writer")    \
-            }                                                                                           \
-            else if(!swmr_reader_exit) {                                                                \
-                if(H5F_vfd_swmr_reader_end_of_tick() < 0)                                               \
-                    HGOTO_ERROR(H5E_FUNC, H5E_CANTSET, err, "end of tick error for VFD SWMR reader")    \
-            }                                                                                           \
-        }                                                                                               \
+#if 1 /* clock_gettime() version */ /* JRM */
+#define VFD_SWMR_TEST_FOR_END_OF_TICK(swmr_reader_exit, err)                  \
+    /* Initialize the library */                                              \
+    if(vfd_swmr_g) {                                                          \
+        struct timespec curr_time;                                            \
+        long curr_nsecs, end_nsecs;                                           \
+        if(HDclock_gettime(CLOCK_MONOTONIC, &curr_time) < 0)                  \
+            HGOTO_ERROR(H5E_FUNC, H5E_CANTGET, err,                           \
+                        "can't get time via clock_gettime")                   \
+        curr_nsecs = curr_time.tv_sec * 1000000000 + curr_time.tv_nsec;       \
+        end_nsecs = end_of_tick_g.tv_sec * 1000000000 + end_of_tick_g.tv_nsec;\
+        if(curr_nsecs > end_nsecs) {                                          \
+            if(vfd_swmr_writer_g) {                                           \
+                if(H5F_vfd_swmr_writer_end_of_tick() < 0)                     \
+                    HGOTO_ERROR(H5E_FUNC, H5E_CANTSET, err,                   \
+                                "end of tick error for VFD SWMR writer")      \
+            }                                                                 \
+            else if(!swmr_reader_exit) {                                      \
+                if(H5F_vfd_swmr_reader_end_of_tick() < 0)                     \
+                    HGOTO_ERROR(H5E_FUNC, H5E_CANTSET, err,                   \
+                                "end of tick error for VFD SWMR reader")      \
+            }                                                                 \
+        }                                                                     \
+    }
+#else /* gettimeofday() version */ /* JRM */
+#define VFD_SWMR_TEST_FOR_END_OF_TICK(swmr_reader_exit, err)                   \
+    /* Initialize the library */                                               \
+    if(vfd_swmr_g) {                                                           \
+        struct timeval curr_time;                                              \
+        if(HDgettimeofday(&curr_time, NULL) < 0)                               \
+            HGOTO_ERROR(H5E_FUNC, H5E_CANTGET, err,                            \
+                        "can't get time via gettimeofday()")                   \
+        if((curr_time.tv_sec >= end_of_tick_g.tv_sec) &&                       \
+           (curr_time.tv_usec >= end_of_tick_g.tv_usec)) {                     \
+            if(vfd_swmr_writer_g) {                                            \
+                if(H5F_vfd_swmr_writer_end_of_tick() < 0)                      \
+                    HGOTO_ERROR(H5E_FUNC, H5E_CANTSET, err,                    \
+                                "end of tick error for VFD SWMR writer")       \
+            }                                                                  \
+            else if(!swmr_reader_exit) {                                       \
+                if(H5F_vfd_swmr_reader_end_of_tick() < 0)                      \
+                    HGOTO_ERROR(H5E_FUNC, H5E_CANTSET, err,                    \
+                           "end of tick error for VFD SWMR reader")            \
+            }                                                                  \
+        }                                                                      \
     }
+#endif /* gettimeofday() version */ /* JRM */
 
 /* Use this macro for all "normal" API functions */
 #define FUNC_ENTER_API(err) {{                                                \