diff options
Diffstat (limited to 'src/H5C.c')
| -rw-r--r-- | src/H5C.c | 551 |
1 files changed, 534 insertions, 17 deletions
@@ -159,6 +159,10 @@ static herr_t H5C__mark_flush_dep_dirty(H5C_cache_entry_t * entry); static herr_t H5C__mark_flush_dep_clean(H5C_cache_entry_t * entry); +static herr_t H5C__serialize_ring(H5F_t *f, hid_t dxpl_id, H5C_ring_t ring); +static herr_t H5C__serialize_single_entry(H5F_t *f, hid_t dxpl_id, + H5C_t *cache_ptr, H5C_cache_entry_t *entry_ptr); + static herr_t H5C__verify_len_eoa(H5F_t *f, const H5C_class_t * type, haddr_t addr, size_t *len, hbool_t actual); @@ -750,20 +754,10 @@ H5C_prep_for_file_close(H5F_t *f, hid_t dxpl_id) /* Make certain there aren't any protected entries */ HDassert(cache_ptr->pl_len == 0); - /* If the file is opened and closed without any access to - * any group or dataset, it is possible that the cache image (if - * it exists) has not been read yet. Do this now if required. - */ - if(cache_ptr->load_image) { - cache_ptr->load_image = FALSE; - if(H5C__load_cache_image(f, dxpl_id) < 0) - HGOTO_ERROR(H5E_CACHE, H5E_CANTLOAD, FAIL, "Can't load cache image") - } /* end if */ + /* Prepare cache image */ + if(H5C__prep_image_for_file_close(f, dxpl_id) < 0) + HGOTO_ERROR(H5E_CACHE, H5E_CANTCREATE, FAIL, "can't create cache image") - /* Generate the cache image, if requested */ - if(cache_ptr->image_ctl.generate_image) - if(H5C__prep_image_for_file_close(f, dxpl_id) < 0) - HGOTO_ERROR(H5E_CACHE, H5E_CANTCREATE, FAIL, "Can't create cache image") done: FUNC_LEAVE_NOAPI(ret_value) @@ -5310,7 +5304,7 @@ H5C_flush_invalidate_ring(H5F_t * f, hid_t dxpl_id, H5C_ring_t ring, H5C_cache_entry_t *entry_ptr = NULL; H5C_cache_entry_t *next_entry_ptr = NULL; #if H5C_DO_SANITY_CHECKS - int64_t initial_slist_len = 0; + uint32_t initial_slist_len = 0; size_t initial_slist_size = 0; #endif /* H5C_DO_SANITY_CHECKS */ herr_t ret_value = SUCCEED; @@ -5545,7 +5539,7 @@ H5C_flush_invalidate_ring(H5F_t * f, hid_t dxpl_id, H5C_ring_t ring, if(node_ptr == NULL) { HDassert(cache_ptr->slist_len == (initial_slist_len + cache_ptr->slist_len_increase)); - HDassert((int64_t)cache_ptr->slist_size == ((int64_t)initial_slist_size + cache_ptr->slist_size_increase)); + HDassert(cache_ptr->slist_size == (initial_slist_size + cache_ptr->slist_size_increase)); } /* end if */ #endif /* H5C_DO_SANITY_CHECKS */ @@ -5747,7 +5741,7 @@ H5C_flush_ring(H5F_t *f, hid_t dxpl_id, H5C_ring_t ring, unsigned flags) H5C_cache_entry_t * entry_ptr = NULL; H5C_cache_entry_t * next_entry_ptr = NULL; #if H5C_DO_SANITY_CHECKS - int64_t initial_slist_len = 0; + uint32_t initial_slist_len = 0; size_t initial_slist_size = 0; #endif /* H5C_DO_SANITY_CHECKS */ int i; @@ -5953,7 +5947,7 @@ H5C_flush_ring(H5F_t *f, hid_t dxpl_id, H5C_ring_t ring, unsigned flags) #if H5C_DO_SANITY_CHECKS /* Verify that the slist size and length are as expected. */ HDassert((initial_slist_len + cache_ptr->slist_len_increase) == cache_ptr->slist_len); - HDassert((size_t)((int64_t)initial_slist_size + cache_ptr->slist_size_increase) == cache_ptr->slist_size); + HDassert((initial_slist_size + cache_ptr->slist_size_increase) == cache_ptr->slist_size); #endif /* H5C_DO_SANITY_CHECKS */ } /* while */ @@ -7996,6 +7990,529 @@ H5C__assert_flush_dep_nocycle(const H5C_cache_entry_t * entry, /*------------------------------------------------------------------------- + * Function: H5C__serialize_cache + * + * Purpose: Serialize (i.e. construct an on disk image) for all entries + * in the metadata cache including clean entries. + * + * Note that flush dependencies and "flush me last" flags + * must be observed in the serialization process. + * + * Note also that entries may be loaded, flushed, evicted, + * expunged, relocated, resized, or removed from the cache + * during this process, just as these actions may occur during + * a regular flush. + * + * However, we are given that the cache will contain no protected + * entries on entry to this routine (although entries may be + * briefly protected and then unprotected during the serialize + * process). + * + * The objective of this routine is serialize all entries and + * to force all entries into their actual locations on disk. + * + * The initial need for this routine is to settle all entries + * in the cache prior to construction of the metadata cache + * image so that the size of the cache image can be calculated. + * However, I gather that other uses for the routine are + * under consideration. + * + * Return: Non-negative on success/Negative on failure or if there was + * a request to flush all items and something was protected. + * + * Programmer: John Mainzer + * 7/22/15 + * + *------------------------------------------------------------------------- + */ +herr_t +H5C__serialize_cache(H5F_t *f, hid_t dxpl_id) +{ +#if H5C_DO_SANITY_CHECKS + int i; + uint32_t index_len = 0; + size_t index_size = (size_t)0; + size_t clean_index_size = (size_t)0; + size_t dirty_index_size = (size_t)0; + size_t slist_size = (size_t)0; + uint32_t slist_len = 0; +#endif /* H5C_DO_SANITY_CHECKS */ + H5C_ring_t ring; + H5C_t * cache_ptr; + herr_t ret_value = SUCCEED; + + FUNC_ENTER_PACKAGE + + /* Sanity checks */ + HDassert(f); + HDassert(f->shared); + cache_ptr = f->shared->cache; + HDassert(cache_ptr); + HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC); + HDassert(cache_ptr->slist_ptr); + +#if H5C_DO_SANITY_CHECKS + HDassert(cache_ptr->index_ring_len[H5C_RING_UNDEFINED] == 0); + HDassert(cache_ptr->index_ring_size[H5C_RING_UNDEFINED] == (size_t)0); + HDassert(cache_ptr->clean_index_ring_size[H5C_RING_UNDEFINED] == (size_t)0); + HDassert(cache_ptr->dirty_index_ring_size[H5C_RING_UNDEFINED] == (size_t)0); + HDassert(cache_ptr->slist_ring_len[H5C_RING_UNDEFINED] == 0); + HDassert(cache_ptr->slist_ring_size[H5C_RING_UNDEFINED] == (size_t)0); + + for(i = H5C_RING_USER; i < H5C_RING_NTYPES; i++) { + index_len += cache_ptr->index_ring_len[i]; + index_size += cache_ptr->index_ring_size[i]; + clean_index_size += cache_ptr->clean_index_ring_size[i]; + dirty_index_size += cache_ptr->dirty_index_ring_size[i]; + + slist_len += cache_ptr->slist_ring_len[i]; + slist_size += cache_ptr->slist_ring_size[i]; + } /* end for */ + + HDassert(cache_ptr->index_len == index_len); + HDassert(cache_ptr->index_size == index_size); + HDassert(cache_ptr->clean_index_size == clean_index_size); + HDassert(cache_ptr->dirty_index_size == dirty_index_size); + HDassert(cache_ptr->slist_len == slist_len); + HDassert(cache_ptr->slist_size == slist_size); +#endif /* H5C_DO_SANITY_CHECKS */ + +#if H5C_DO_EXTREME_SANITY_CHECKS + if((H5C_validate_protected_entry_list(cache_ptr) < 0) || + (H5C_validate_pinned_entry_list(cache_ptr) < 0) || + (H5C_validate_lru_list(cache_ptr) < 0)) + HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "an extreme sanity check failed on entry") +#endif /* H5C_DO_EXTREME_SANITY_CHECKS */ + +#ifndef NDEBUG + /* if this is a debug build, set the serialization_count field of + * each entry in the cache to zero before we start the serialization. + * This allows us to detect the case in which any entry is serialized + * more than once (a performance issues), and more importantly, the + * case is which any flush depencency parent is serializes more than + * once (a correctness issue). + */ + { + H5C_cache_entry_t * scan_ptr = NULL; + + scan_ptr = cache_ptr->il_head; + while(scan_ptr != NULL) { + HDassert(scan_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC); + scan_ptr->serialization_count = 0; + scan_ptr = scan_ptr->il_next; + } /* end while */ + } /* end block */ +#endif /* NDEBUG */ + + /* set cache_ptr->serialization_in_progress to TRUE, and back + * to FALSE at the end of the function. Must maintain this flag + * to support H5C_get_serialization_in_progress(), which is in + * turn required to support sanity checking in some cache + * clients. + */ + HDassert(!cache_ptr->serialization_in_progress); + cache_ptr->serialization_in_progress = TRUE; + + /* Serialize each ring, starting from the outermost ring and + * working inward. + */ + ring = H5C_RING_USER; + while(ring < H5C_RING_NTYPES) { + HDassert(cache_ptr->close_warning_received); + switch(ring) { + case H5C_RING_USER: + break; + + case H5C_RING_RDFSM: + if(!cache_ptr->rdfsm_settled) { + hbool_t fsm_settled = FALSE; /* Whether the FSM was actually settled */ + + /* Settle raw data FSM */ + if(H5MF_settle_raw_data_fsm(f, dxpl_id, &fsm_settled) < 0) + HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "RD FSM settle failed") + + /* Only set the flag if the FSM was actually settled */ + if(fsm_settled) + cache_ptr->rdfsm_settled = TRUE; + } /* end if */ + break; + + case H5C_RING_MDFSM: + if(!cache_ptr->mdfsm_settled) { + hbool_t fsm_settled = FALSE; /* Whether the FSM was actually settled */ + + /* Settle metadata FSM */ + if(H5MF_settle_meta_data_fsm(f, dxpl_id, &fsm_settled) < 0) + HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "MD FSM settle failed") + + /* Only set the flag if the FSM was actually settled */ + if(fsm_settled) + cache_ptr->mdfsm_settled = TRUE; + } /* end if */ + break; + + case H5C_RING_SBE: + case H5C_RING_SB: + break; + + default: + HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Unknown ring?!?!") + break; + } /* end switch */ + + if(H5C__serialize_ring(f, dxpl_id, ring) < 0) + HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "serialize ring failed") + + ring++; + } /* end while */ + +#ifndef NDEBUG + /* Verify that no entry has been serialized more than once. + * FD parents with multiple serializations should have been caught + * elsewhere, so no specific check for them here. + */ + { + H5C_cache_entry_t * scan_ptr = NULL; + + scan_ptr = cache_ptr->il_head; + while(scan_ptr != NULL) { + HDassert(scan_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC); + HDassert(scan_ptr->serialization_count <= 1); + + scan_ptr = scan_ptr->il_next; + } /* end while */ + } /* end block */ +#endif /* NDEBUG */ + +done: + cache_ptr->serialization_in_progress = FALSE; + FUNC_LEAVE_NOAPI(ret_value) +} /* H5C__serialize_cache() */ + + +/*------------------------------------------------------------------------- + * Function: H5C__serialize_ring + * + * Purpose: Serialize the entries contained in the specified cache and + * ring. All entries in rings outside the specified ring + * must have been serialized on entry. + * + * If the cache contains protected entries in the specified + * ring, the function will fail, as protected entries cannot + * be serialized. However all unprotected entries in the + * target ring should be serialized before the function + * returns failure. + * + * If flush dependencies appear in the target ring, the + * function makes repeated passes through the index list + * serializing entries in flush dependency order. + * + * All entries outside the H5C_RING_SBE are marked for + * inclusion in the cache image. Entries in H5C_RING_SBE + * and below are marked for exclusion from the image. + * + * Return: Non-negative on success/Negative on failure or if there was + * a request to flush all items and something was protected. + * + * Programmer: John Mainzer + * 9/11/15 + * + *------------------------------------------------------------------------- + */ +static herr_t +H5C__serialize_ring(H5F_t *f, hid_t dxpl_id, H5C_ring_t ring) +{ + hbool_t done = FALSE; + H5C_t * cache_ptr; + H5C_cache_entry_t * entry_ptr; + herr_t ret_value = SUCCEED; + + FUNC_ENTER_STATIC + + /* Sanity checks */ + HDassert(f); + HDassert(f->shared); + cache_ptr = f->shared->cache; + HDassert(cache_ptr); + HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC); + HDassert(ring > H5C_RING_UNDEFINED); + HDassert(ring < H5C_RING_NTYPES); + + HDassert(cache_ptr->serialization_in_progress); + + /* The objective here is to serialize all entries in the cache ring + * in flush dependency order. + * + * The basic algorithm is to scan the cache index list looking for + * unserialized entries that are either not in a flush dependency + * relationship, or which have no unserialized children. Any such + * entry is serialized and its flush dependency parents (if any) are + * informed -- allowing them to decrement their userialized child counts. + * + * However, this algorithm is complicated by the ability + * of client serialization callbacks to perform operations on + * on the cache which can result in the insertion, deletion, + * relocation, resize, dirty, flush, eviction, or removal (via the + * take ownership flag) of entries. Changes in the flush dependency + * structure are also possible. + * + * On the other hand, the algorithm is simplified by the fact that + * we are serializing, not flushing. Thus, as long as all entries + * are serialized correctly, it doesn't matter if we have to go back + * and serialize an entry a second time. + * + * These possible actions result in the following modfications to + * tha basic algorithm: + * + * 1) In the event of an entry expunge, eviction or removal, we must + * restart the scan as it is possible that the next entry in our + * scan is no longer in the cache. Were we to examine this entry, + * we would be accessing deallocated memory. + * + * 2) A resize, dirty, or insertion of an entry may result in the + * the increment of a flush dependency parent's dirty and/or + * unserialized child count. In the context of serializing the + * the cache, this is a non-issue, as even if we have already + * serialized the parent, it will be marked dirty and its image + * marked out of date if appropriate when the child is serialized. + * + * However, this is a major issue for a flush, as were this to happen + * in a flush, it would violate the invariant that the flush dependency + * feature is intended to enforce. As the metadata cache has no + * control over the behavior of cache clients, it has no way of + * preventing this behaviour. However, it should detect it if at all + * possible. + * + * Do this by maintaining a count of the number of times each entry is + * serialized during a cache serialization. If any flush dependency + * parent is serialized more than once, throw an assertion failure. + * + * 3) An entry relocation will typically change the location of the + * entry in the index list. This shouldn't cause problems as we + * will scan the index list until we make a complete pass without + * finding anything to serialize -- making relocations of either + * the current or next entries irrelevant. + * + * Note that since a relocation may result in our skipping part of + * the index list, we must always do at least one more pass through + * the index list after an entry relocation. + * + * 4) Changes in the flush dependency structure are possible on + * entry insertion, load, expunge, evict, or remove. Destruction + * of a flush dependency has no effect, as it can only relax the + * flush dependencies. Creation of a flush dependency can create + * an unserialized child of a flush dependency parent where all + * flush dependency children were previously serialized. Should + * this child dirty the flush dependency parent when it is serialized, + * the parent will be re-serialized. + * + * Per the discussion of 2) above, this is a non issue for cache + * serialization, and a major problem for cache flush. Using the + * same detection mechanism, throw an assertion failure if this + * condition appears. + * + * Observe that either eviction or removal of entries as a result of + * a serialization is not a problem as long as the flush depencency + * tree does not change beyond the removal of a leaf. + */ + while(!done) { + /* Reset the counters so that we can detect insertions, loads, + * moves, and flush dependency height changes caused by the pre_serialize + * and serialize callbacks. + */ + cache_ptr->entries_loaded_counter = 0; + cache_ptr->entries_inserted_counter = 0; + cache_ptr->entries_relocated_counter = 0; + + done = TRUE; /* set to FALSE if any activity in inner loop */ + entry_ptr = cache_ptr->il_head; + while(entry_ptr != NULL) { + HDassert(entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC); + + /* Verify that either the entry is already serialized, or + * that it is assigned to either the target or an inner + * ring. + */ + HDassert((entry_ptr->ring >= ring) || (entry_ptr->image_up_to_date)); + + /* Skip flush me last entries or inner ring entries */ + if(!entry_ptr->flush_me_last && entry_ptr->ring == ring) { + + /* if we encounter an unserialized entry in the current + * ring that is not marked flush me last, we are not done. + */ + if(!entry_ptr->image_up_to_date) + done = FALSE; + + /* Serialize the entry if its image is not up to date + * and it has no unserialized flush dependency children. + */ + if(!entry_ptr->image_up_to_date && entry_ptr->flush_dep_nunser_children == 0) { + HDassert(entry_ptr->serialization_count == 0); + + /* Serialize the entry */ + if(H5C__serialize_single_entry(f, dxpl_id, cache_ptr, entry_ptr) < 0) + HGOTO_ERROR(H5E_CACHE, H5E_CANTSERIALIZE, FAIL, "entry serialization failed") + + HDassert(entry_ptr->flush_dep_nunser_children == 0); + HDassert(entry_ptr->serialization_count == 0); + +#ifndef NDEBUG + /* Increment serialization counter (to detect multiple serializations) */ + entry_ptr->serialization_count++; +#endif /* NDEBUG */ + } /* end if */ + } /* end if */ + + /* Check for the cache being perturbed during the entry serialize */ + if((cache_ptr->entries_loaded_counter > 0) || + (cache_ptr->entries_inserted_counter > 0) || + (cache_ptr->entries_relocated_counter > 0)) { + +#if H5C_COLLECT_CACHE_STATS + H5C__UPDATE_STATS_FOR_INDEX_SCAN_RESTART(cache_ptr); +#endif /* H5C_COLLECT_CACHE_STATS */ + + /* Reset the counters */ + cache_ptr->entries_loaded_counter = 0; + cache_ptr->entries_inserted_counter = 0; + cache_ptr->entries_relocated_counter = 0; + + /* Restart scan */ + entry_ptr = cache_ptr->il_head; + } /* end if */ + else + /* Advance to next entry */ + entry_ptr = entry_ptr->il_next; + } /* while ( entry_ptr != NULL ) */ + } /* while ( ! done ) */ + + + /* Reset the counters so that we can detect insertions, loads, + * moves, and flush dependency height changes caused by the pre_serialize + * and serialize callbacks. + */ + cache_ptr->entries_loaded_counter = 0; + cache_ptr->entries_inserted_counter = 0; + cache_ptr->entries_relocated_counter = 0; + + /* At this point, all entries not marked "flush me last" and in + * the current ring or outside it should be serialized and have up + * to date images. Scan the index list again to serialize the + * "flush me last" entries (if they are in the current ring) and to + * verify that all other entries have up to date images. + */ + entry_ptr = cache_ptr->il_head; + while(entry_ptr != NULL) { + HDassert(entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC); + HDassert(entry_ptr->ring > H5C_RING_UNDEFINED); + HDassert(entry_ptr->ring < H5C_RING_NTYPES); + HDassert((entry_ptr->ring >= ring) || (entry_ptr->image_up_to_date)); + + if(entry_ptr->ring == ring) { + if(entry_ptr->flush_me_last) { + if(!entry_ptr->image_up_to_date) { + HDassert(entry_ptr->serialization_count == 0); + HDassert(entry_ptr->flush_dep_nunser_children == 0); + + /* Serialize the entry */ + if(H5C__serialize_single_entry(f, dxpl_id, cache_ptr, entry_ptr) < 0) + HGOTO_ERROR(H5E_CACHE, H5E_CANTSERIALIZE, FAIL, "entry serialization failed") + + /* Check for the cache changing */ + if((cache_ptr->entries_loaded_counter > 0) || + (cache_ptr->entries_inserted_counter > 0) || + (cache_ptr->entries_relocated_counter > 0)) + HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "flush_me_last entry serialization triggered restart") + + HDassert(entry_ptr->flush_dep_nunser_children == 0); + HDassert(entry_ptr->serialization_count == 0); +#ifndef NDEBUG + /* Increment serialization counter (to detect multiple serializations) */ + entry_ptr->serialization_count++; +#endif /* NDEBUG */ + } /* end if */ + } /* end if */ + else { + HDassert(entry_ptr->image_up_to_date); + HDassert(entry_ptr->serialization_count <= 1); + HDassert(entry_ptr->flush_dep_nunser_children == 0); + } /* end else */ + } /* if ( entry_ptr->ring == ring ) */ + + entry_ptr = entry_ptr->il_next; + } /* while ( entry_ptr != NULL ) */ + +done: + HDassert(cache_ptr->serialization_in_progress); + FUNC_LEAVE_NOAPI(ret_value) +} /* H5C__serialize_ring() */ + + +/*------------------------------------------------------------------------- + * Function: H5C__serialize_single_entry + * + * Purpose: Serialize the cache entry pointed to by the entry_ptr + * parameter. + * + * Return: Non-negative on success/Negative on failure + * + * Programmer: John Mainzer, 7/24/15 + * + *------------------------------------------------------------------------- + */ +static herr_t +H5C__serialize_single_entry(H5F_t *f, hid_t dxpl_id, H5C_t *cache_ptr, + H5C_cache_entry_t *entry_ptr) +{ + herr_t ret_value = SUCCEED; /* Return value */ + + FUNC_ENTER_STATIC + + /* Sanity checks */ + HDassert(f); + HDassert(cache_ptr); + HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC); + HDassert(entry_ptr); + HDassert(entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC); + HDassert(!entry_ptr->prefetched); + HDassert(!entry_ptr->image_up_to_date); + HDassert(entry_ptr->is_dirty); + HDassert(!entry_ptr->is_protected); + HDassert(!entry_ptr->flush_in_progress); + HDassert(entry_ptr->type); + + /* Set entry_ptr->flush_in_progress to TRUE so the the target entry + * will not be evicted out from under us. Must set it back to FALSE + * when we are done. + */ + entry_ptr->flush_in_progress = TRUE; + + /* Allocate buffer for the entry image if required. */ + if(NULL == entry_ptr->image_ptr) { + HDassert(entry_ptr->size > 0); + if(NULL == (entry_ptr->image_ptr = H5MM_malloc(entry_ptr->size + H5C_IMAGE_EXTRA_SPACE)) ) + HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "memory allocation failed for on disk image buffer") +#if H5C_DO_MEMORY_SANITY_CHECKS + HDmemcpy(((uint8_t *)entry_ptr->image_ptr) + image_size, H5C_IMAGE_SANITY_VALUE, H5C_IMAGE_EXTRA_SPACE); +#endif /* H5C_DO_MEMORY_SANITY_CHECKS */ + } /* end if */ + + /* Generate image for entry */ + if(H5C__generate_image(f, cache_ptr, entry_ptr, dxpl_id) < 0) + HGOTO_ERROR(H5E_CACHE, H5E_CANTSERIALIZE, FAIL, "Can't generate image for cache entry") + + /* Reset the flush_in progress flag */ + entry_ptr->flush_in_progress = FALSE; + +done: + HDassert((ret_value != SUCCEED) || (!entry_ptr->flush_in_progress)); + HDassert((ret_value != SUCCEED) || (entry_ptr->image_up_to_date)); + FUNC_LEAVE_NOAPI(ret_value) +} /* H5C__serialize_single_entry() */ + + +/*------------------------------------------------------------------------- * Function: H5C__generate_image * * Purpose: Serialize an entry and generate its image. |