tal/link: new module for reference-count style coding for tal.

[ccan] / ccan / tal / link / link.h

diff --git a/ccan/tal/link/link.h b/ccan/tal/link/link.h
new file mode 100644 (file)
index 0000000..18d598b
--- /dev/null
+++ b/ccan/tal/link/link.h
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+/* Licensed under BSD-MIT - see LICENSE file for details */
+#ifndef TAL_LINK_H
+#define TAL_LINK_H
+#include "config.h"
+#include <ccan/tal/tal.h>
+
+/**
+ * tal_linkable - set up a tal object to be linkable.
+ * @newobj - the newly allocated object (with a NULL parent)
+ *
+ * The object will be freed when @newobj is freed or the last talloc_link()
+ * is talloc_delink'ed.
+ *
+ * Returns @newobj or NULL (if an allocation fails).
+ *
+ * Example:
+ *     int *shared_count;
+ *
+ *     shared_count = tal_linkable(talz(NULL, int));
+ *     assert(shared_count);
+ */
+#define tal_linkable(newobj) \
+       (tal_typeof(newobj) tal_linkable_((newobj)))
+
+/**
+ * tal_link - add a(nother) link to a linkable object.
+ * @ctx - the context to link to (parent of the resulting link)
+ * @obj - the object previously made linkable with talloc_linked().
+ *
+ * If @ctx is non-NULL, the link will be a child of @ctx, and this freed
+ * when @ctx is.
+ *
+ * Returns NULL on failure (out of memory).
+ *
+ * Example:
+ *     void *my_ctx = NULL;
+ *
+ *     tal_link(my_ctx, shared_count);
+ */
+#if HAVE_STATEMENT_EXPR
+/* Weird macro avoids gcc's 'warning: value computed is not used'. */
+#define tal_link(ctx, obj)                             \
+       ({ tal_typeof(obj) tal_link_((ctx), (obj)); })
+#else
+#define tal_link(ctx, obj)                             \
+       (tal_typeof(obj) tal_link_((ctx), (obj)))
+#endif
+
+/**
+ * tal_delink - explicitly remove a link from a linkable object.
+ * @ctx - the context to link to (parent of the resulting link)
+ * @obj - the object previously made linkable with talloc_linked().
+ *
+ * Explicitly remove a link: normally it is implied by freeing @ctx.
+ * Removing the last link frees the object.  If @obj is NULL, nothing
+ * is done.
+ *
+ * Example:
+ *     tal_delink(my_ctx, shared_count);
+ */
+#define tal_delink(ctx, obj)                           \
+       tal_delink_((ctx), (obj))
+
+/* Internal helpers. */
+void *tal_linkable_(tal_t *newobj);
+void *tal_link_(const tal_t *ctx, const tal_t *dest);
+void tal_delink_(const tal_t *ctx, const tal_t *dest);
+
+#endif /* TAL_LINK_H */