tal: adding or removing a notifier/destructor can be const.

[ccan] / ccan / tal / tal.h

diff --git a/ccan/tal/tal.h b/ccan/tal/tal.h
index 1ed15c75f46fd664b6f57b10c65bcd8eb9790406..10ee460812bd10860adf450abebf17e2ede85988 100644 (file)
--- a/ccan/tal/tal.h
+++ b/ccan/tal/tal.h
@@ -53,14 +53,15 @@ typedef void tal_t;
  * @p: NULL, or tal allocated object to free.
  *
  * This calls the destructors for p (if any), then does the same for all its
- * children (recursively) before finally freeing the memory.
+ * children (recursively) before finally freeing the memory.  It returns
+ * NULL, for convenience.
  *
  * Note: errno is preserved by this call.
  *
  * Example:
- *     tal_free(p);
+ *     p = tal_free(p);
  */
-void tal_free(const tal_t *p);
+void *tal_free(const tal_t *p);
 
 /**
  * tal_arr - allocate an array of objects.
@@ -125,10 +126,92 @@ void tal_free(const tal_t *p);
  * tal_add_destructor - add a callback function when this context is destroyed.
  * @ptr: The tal allocated object.
  * @function: the function to call before it's freed.
+ *
+ * This is a more convenient form of tal_add_notifier(@ptr,
+ * TAL_NOTIFY_FREE, ...), in that the function prototype takes only @ptr.
+ *
+ * Note that this can only fail if your allocfn fails and your errorfn returns.
  */
 #define tal_add_destructor(ptr, function)                                    \
        tal_add_destructor_((ptr), typesafe_cb(void, void *, (function), (ptr)))
 
+/**
+ * tal_del_destructor - remove a destructor callback function.
+ * @ptr: The tal allocated object.
+ * @function: the function to call before it's freed.
+ *
+ * If @function has not been successfully added as a destructor, this returns
+ * false.
+ */
+#define tal_del_destructor(ptr, function)                                    \
+       tal_del_destructor_((ptr), typesafe_cb(void, void *, (function), (ptr)))
+
+enum tal_notify_type {
+       TAL_NOTIFY_FREE = 1,
+       TAL_NOTIFY_STEAL = 2,
+       TAL_NOTIFY_MOVE = 4,
+       TAL_NOTIFY_RESIZE = 8,
+       TAL_NOTIFY_RENAME = 16,
+       TAL_NOTIFY_ADD_CHILD = 32,
+       TAL_NOTIFY_DEL_CHILD = 64,
+       TAL_NOTIFY_ADD_NOTIFIER = 128,
+       TAL_NOTIFY_DEL_NOTIFIER = 256
+};
+
+/**
+ * tal_add_notifier - add a callback function when this context changes.
+ * @ptr: The tal allocated object.
+ * @types: Bitwise OR of the types the callback is interested in.
+ * @callback: the function to call.
+ *
+ * Note that this can only fail if your allocfn fails and your errorfn
+ * returns.  Also note that notifiers are not reliable in the case
+ * where an allocation fails, as they may be called before any
+ * allocation is actually done.
+ *
+ * TAL_NOTIFY_FREE is called when @ptr is freed, either directly or
+ * because an ancestor is freed: @info is the argument to tal_free().
+ * It is exactly equivalent to a destructor, with more information.
+ *
+ * TAL_NOTIFY_STEAL is called when @ptr's parent changes: @info is the
+ * new parent.
+ *
+ * TAL_NOTIFY_MOVE is called when @ptr is realloced (via tal_resize)
+ * and moved.  In this case, @ptr arg here is the new memory, and
+ * @info is the old pointer.
+ *
+ * TAL_NOTIFY_RESIZE is called when @ptr is realloced via tal_resize:
+ * @info is the new size, in bytes.  If the pointer has moved,
+ * TAL_NOTIFY_MOVE callbacks are called first.
+ *
+ * TAL_NOTIFY_ADD_CHILD/TAL_NOTIFY_DEL_CHILD are called when @ptr is
+ * the context for a tal() allocating call, or a direct child is
+ * tal_free()d: @info is the child.  Note that TAL_NOTIFY_DEL_CHILD is
+ * not called when this context is tal_free()d: TAL_NOTIFY_FREE is
+ * considered sufficient for that case.
+ *
+ * TAL_NOTIFY_ADD_NOTIFIER/TAL_NOTIFIER_DEL_NOTIFIER are called when a
+ * notifier is added or removed (not for this notifier): @info is the
+ * callback.  This is also called for tal_add_destructor and
+ * tal_del_destructor.
+ */
+#define tal_add_notifier(ptr, types, callback)                         \
+       tal_add_notifier_((ptr), (types),                               \
+                         typesafe_cb_postargs(void, tal_t *, (callback), \
+                                              (ptr),                   \
+                                              enum tal_notify_type, void *))
+
+/**
+ * tal_del_notifier - remove a notifier callback function.
+ * @ptr: The tal allocated object.
+ * @callback: the function to call.
+ */
+#define tal_del_notifier(ptr, callback)                                        \
+       tal_del_notifier_((ptr),                                        \
+                         typesafe_cb_postargs(void, void *, (callback), \
+                                              (ptr),                   \
+                                              enum tal_notify_type, void *))
+
 /**
  * tal_set_name - attach a name to a tal pointer.
  * @ptr: The tal allocated object.
@@ -322,6 +405,13 @@ tal_t *tal_steal_(const tal_t *new_parent, const tal_t *t);
 
 bool tal_resize_(tal_t **ctxp, size_t size);
 
-bool tal_add_destructor_(tal_t *ctx, void (*destroy)(void *me));
+bool tal_add_destructor_(const tal_t *ctx, void (*destroy)(void *me));
+bool tal_del_destructor_(const tal_t *ctx, void (*destroy)(void *me));
 
+bool tal_add_notifier_(const tal_t *ctx, enum tal_notify_type types,
+                      void (*notify)(tal_t *ctx, enum tal_notify_type,
+                                     void *info));
+bool tal_del_notifier_(const tal_t *ctx,
+                      void (*notify)(tal_t *ctx, enum tal_notify_type,
+                                     void *info));
 #endif /* CCAN_TAL_H */