[t:5153] fix the error handling code for toku_ltm_get_lt() and better explain...

[t:5153] fix the error handling code for toku_ltm_get_lt() and better explain what the client contract is for the on_create and on_close callbacks.

the idea is you should only pass an on_create callback if there is also an on_close callback, and vice-versa. the on_create callback is called if
the lock tree is created and the on_close callback is called only if the on_create callback was actually called, either because of a user close
of the locktree or by an error path in toku_ltm_get_lt().

we never assume that either of these callbacks are non-null and we know both can be called at most once.


git-svn-id: file:///svn/toku/tokudb@45002 c7de825b-a66e-492c-adef-691d508d4ae1

src/lock_tree/locktree.c

@@ -1353,6 +1353,13 @@ toku_ltm_get_lt(toku_ltm* mgr, toku_lock_tree** ptree, DICTIONARY_ID dict_id, DE
     toku_lock_tree* tree = NULL;
     bool added_to_ltm    = FALSE;
     bool added_to_idlth  = FALSE;
+
+    // verify that the on_create and on_close callbacks are either 
+    // mutually null or mutually non-null.
+    if ((on_close_callback == NULL) != (on_close_callback == NULL)) {
+        r = EINVAL;
+        goto out;
+    }
     
     ltm_mutex_lock(mgr);
     map = toku_idlth_find(mgr->idlth, dict_id);
@@ -1370,11 +1377,15 @@ toku_ltm_get_lt(toku_ltm* mgr, toku_lock_tree** ptree, DICTIONARY_ID dict_id, DE
     if (r != 0) {
         goto cleanup;
     }
-    // we just created the locktree, so call the callback if necessary
+
+    // we just created the locktree, so call the callback if necessary,
+    // and set the on_close callback. we checked above that these callbacks
+    // are either mutually null or non-null, so this is correct.
     if (on_create_callback) {
         on_create_callback(tree, on_create_extra);
+    } else {
+        assert(on_close_callback == NULL);
     }
-    // set the on close callback
     tree->on_close_callback = on_close_callback;
     
     lt_set_dict_id(tree, dict_id);
@@ -1406,22 +1417,24 @@ toku_ltm_get_lt(toku_ltm* mgr, toku_lock_tree** ptree, DICTIONARY_ID dict_id, DE
     if (r == 0) {
         mgr->STATUS_VALUE(LTM_LT_CREATE)++;
         mgr->STATUS_VALUE(LTM_LT_NUM)++;
-        if (mgr->STATUS_VALUE(LTM_LT_NUM) > mgr->STATUS_VALUE(LTM_LT_NUM_MAX))
+        if (mgr->STATUS_VALUE(LTM_LT_NUM) > mgr->STATUS_VALUE(LTM_LT_NUM_MAX)) {
             mgr->STATUS_VALUE(LTM_LT_NUM_MAX) = mgr->STATUS_VALUE(LTM_LT_NUM);
+        }
     }
     else {
         if (tree != NULL) {
-            if (added_to_ltm)
+            if (added_to_ltm) {
                 ltm_remove_lt(mgr, tree);
-            if (added_to_idlth)
+            }
+            if (added_to_idlth) {
                 toku_idlth_delete(mgr->idlth, dict_id);
+            }
+            // if the on_create callback was called, then we will have set
+            // the on_close callback to something non-null, and it will
+            // be called in toku_lt_close(), as required.
             toku_lt_close(tree); 
         }
         mgr->STATUS_VALUE(LTM_LT_CREATE_FAIL)++;
-        // need to make sure the on close callback is called
-        // here, otherwise we might leak something from the 
-        // on create callback.
-        on_close_callback(tree);
     }
     ltm_mutex_unlock(mgr);
     return r;

src/lock_tree/locktree.h

@@ -119,8 +119,12 @@ void
 toku_lt_update_descriptor(toku_lock_tree* tree, DESCRIPTOR desc);
 
 /**
-    Gets a lock tree for a given DB with id dict_id. If the locktree is created,
-    the on_create_callback will be called with a pointer to the new tree and extra.
+    Gets a lock tree for a given DB with id dict_id. 
+
+    If an on_create callback is given, then an on_close callback must be given,
+    and vice-versa. The on_create callback is called if the locktree is actually
+    created by this call and the on_close callback is called when the locktree
+    eventually closes, by the user or by an error path in this call.
 */
 int toku_ltm_get_lt(toku_ltm* mgr, toku_lock_tree** ptree, DICTIONARY_ID dict_id, DESCRIPTOR desc, 
         toku_dbt_cmp compare_fun, toku_lt_on_create_cb on_create_callback, void *on_create_extra,