[t:4904] Closes #4904 Simplify ft_get_some_existing_handle

Now verifies there is exactly one handle and returns it.
Removing this code entirely would make refcounting more complicated.

git-svn-id: file:///svn/toku/tokudb@44225 c7de825b-a66e-492c-adef-691d508d4ae1

ft/ft.c

@@ -576,14 +576,12 @@ int toku_remove_ft (FT h, char **error_string, BOOL oplsn_valid, LSN oplsn) {
     return r;
 }
 
-// gets the first existing BRT handle, if it exists. If no BRT handle exists
-// for this header, returns NULL
-FT_HANDLE toku_ft_get_some_existing_ft_handle(FT h) {
+// Verifies there exists exactly one ft handle and returns it.
+FT_HANDLE toku_ft_get_only_existing_ft_handle(FT h) {
     FT_HANDLE ft_handle_ret = NULL;
     toku_ft_grab_reflock(h);
-    if (!toku_list_empty(&h->live_ft_handles)) {
-        ft_handle_ret = toku_list_struct(toku_list_head(&h->live_ft_handles), struct ft_handle, live_ft_handle_link);
-    }
+    assert(toku_list_num_elements_est(&h->live_ft_handles) == 1);
+    ft_handle_ret = toku_list_struct(toku_list_head(&h->live_ft_handles), struct ft_handle, live_ft_handle_link);
     toku_ft_release_reflock(h);
     return ft_handle_ret;
 }

ft/ft.h

@@ -46,7 +46,7 @@ int toku_ft_needed_unlocked(FT h);
 BOOL toku_ft_has_one_reference_unlocked(FT ft);
 int toku_remove_ft (FT h, char **error_string, BOOL oplsn_valid, LSN oplsn)  __attribute__ ((warn_unused_result));
 
-FT_HANDLE toku_ft_get_some_existing_ft_handle(FT h);
+FT_HANDLE toku_ft_get_only_existing_ft_handle(FT h);
 
 void toku_ft_note_hot_begin(FT_HANDLE brt);
 void toku_ft_note_hot_complete(FT_HANDLE brt, BOOL success, MSN msn_at_start_of_hot);

ft/logger.c

@@ -216,8 +216,7 @@ toku_logger_close_rollback(TOKULOGGER logger, BOOL recovery_failed) {
                 toku_block_verify_no_data_blocks_except_root_unlocked(ft->blocktable, ft->h->root_blocknum);
             }
             assert(!ft->h->dirty);
-            ft_to_close = toku_ft_get_some_existing_ft_handle(ft);
-            assert(ft_to_close);
+            ft_to_close = toku_ft_get_only_existing_ft_handle(ft);
             {
                 BOOL is_empty;
                 is_empty = toku_ft_is_empty_fast(ft_to_close);