Add unit_reset() function

Author: df7cb

README.md

@@ -148,7 +148,8 @@ steps are repeated with the trailing 's' removed.
 
 If the unit definition could be resolved, the result is stored in a
 backend-local hash table to speed up the next lookup. (The function
-`unit_is_hashed()` reports if a given unit name is already cached.)
+`unit_is_hashed()` reports if a given unit name is already cached. The function
+`unit_reset()` clears the hash table. Use it if unit definitions are changed.)
 
 The `definition` column is only provided for information on how the unit was
 originally defined.
@@ -187,6 +188,11 @@ INSERT 0 1
  104.166666666667 legobricks
 ```
 
+*Note: If user-defined (or built-in) units are changed by updating the tables,
+call `unit_reset()` to clear the hash table that caches the lookup result.
+Otherwise, sessions that have already used the unit will continue the old
+definition.*
+
 Input Syntax
 ------------
 
@@ -244,6 +250,8 @@ function stddev_pop(unit)
 function stddev_samp(unit)
 function stddev(unit)
 function sum(unit)
+function unit_is_hashed(cstring)
+function unit_reset()
 function value(unit)
 function variance(unit)
 function var_pop(unit)

expected/custom.out

@@ -52,3 +52,28 @@ SELECT * FROM unit_units WHERE dump;
  legobrick | 9.6 mm |       |            | t
 (1 row)
 
+UPDATE unit_units SET unit = '19.1 mm' WHERE name = 'legobrick'; -- Duplo size
+SELECT '2 legobricks'::unit AS old_size;
+ old_size 
+----------
+ 19.2 mm
+(1 row)
+
+SELECT unit_reset();
+ unit_reset 
+------------
+ 
+(1 row)
+
+SELECT unit_is_hashed('legobricks');
+ unit_is_hashed 
+----------------
+ f
+(1 row)
+
+SELECT '2 legobricks'::unit AS new_size;
+ new_size 
+----------
+ 38.2 mm
+(1 row)
+

sql/custom.sql

@@ -10,3 +10,9 @@ SELECT unit_is_hashed('legobricks');
 SELECT '1 m'::unit @ 'legobricks' AS one_meter;
 SELECT unit_is_hashed('legobricks');
 SELECT * FROM unit_units WHERE dump;
+
+UPDATE unit_units SET unit = '19.1 mm' WHERE name = 'legobrick'; -- Duplo size
+SELECT '2 legobricks'::unit AS old_size;
+SELECT unit_reset();
+SELECT unit_is_hashed('legobricks');
+SELECT '2 legobricks'::unit AS new_size;

unit--2--3.sql.in

@@ -59,3 +59,8 @@ CREATE FUNCTION unit_is_hashed(cstring)
 	RETURNS bool
 	AS '$libdir/unit'
 	LANGUAGE C VOLATILE STRICT;
+
+CREATE FUNCTION unit_reset()
+	RETURNS void
+	AS '$libdir/unit'
+	LANGUAGE C VOLATILE STRICT;

unit--3.sql.in

@@ -592,3 +592,8 @@ CREATE FUNCTION unit_is_hashed(cstring)
 	RETURNS bool
 	AS '$libdir/unit'
 	LANGUAGE C VOLATILE STRICT;
+
+CREATE FUNCTION unit_reset()
+	RETURNS void
+	AS '$libdir/unit'
+	LANGUAGE C VOLATILE STRICT;

unit.c

@@ -893,3 +893,16 @@ unit_is_hashed(PG_FUNCTION_ARGS)
 
 	PG_RETURN_BOOL (hash_search(unit_names, name, HASH_FIND, NULL) != NULL);
 }
+
+PG_FUNCTION_INFO_V1(unit_reset);
+
+Datum
+unit_reset(PG_FUNCTION_ARGS)
+{
+	/* reinitialize hash tables */
+	hash_destroy(unit_names);
+	hash_destroy(unit_dimensions);
+	unit_get_definitions();
+
+	PG_RETURN_VOID();
+}