Add json_object_array_shrink() (and array_list_shrink()) and use it in json_tokener to minimize the amount of memory used. This results in a 39%-50% reduction in memory use (peak RSS, peak heap usage) on the jc-bench benchmark and 9% shorter runtime.

Also add the json_object_new_array_ext, array_list_new2, and array_list_shrink functions.

arraylist.h

@@ -37,8 +37,27 @@ struct array_list
 };
 typedef struct array_list array_list;
 
+/**
+ * Allocate an array_list of the default size (32).
+ * @deprecated Use array_list_new2() instead.
+ */
 extern struct array_list *array_list_new(array_list_free_fn *free_fn);
 
+/**
+ * Allocate an array_list of the desired size.
+ *
+ * If possible, the size should be chosen to closely match
+ * the actual number of elements expected to be used.
+ * If the exact size is unknown, there are tradeoffs to be made:
+ * - too small - the array_list code will need to call realloc() more
+ *   often (which might incur an additional memory copy).
+ * - too large - will waste memory, but that can be mitigated
+ *   by calling array_list_shrink() once the final size is known.
+ *
+ * @see array_list_shrink
+ */
+extern struct array_list *array_list_new2(array_list_free_fn *free_fn, int initial_size);
+
 extern void array_list_free(struct array_list *al);
 
 extern void *array_list_get_idx(struct array_list *al, size_t i);
@@ -56,6 +75,14 @@ extern void *array_list_bsearch(const void **key, struct array_list *arr,
 
 extern int array_list_del_idx(struct array_list *arr, size_t idx, size_t count);
 
+
+/**
+ * Shrink the array list to just enough to fit the number of elements in it,
+ * plus empty_slots.
+ */
+extern int array_list_shrink(struct array_list *arr, size_t empty_slots);
+
+
 #ifdef __cplusplus
 }
 #endif