diff --git a/spa/include/spa/utils/hook.h b/spa/include/spa/utils/hook.h index 530906bff..0d85da7b3 100644 --- a/spa/include/spa/utils/hook.h +++ b/spa/include/spa/utils/hook.h @@ -212,26 +212,86 @@ struct spa_interface { * \} */ -/** \defgroup spa_hook SPA Hooks +/** \defgroup spa_hooks SPA Hooks * - * \brief a list of hooks + * A SPA Hook is a data structure to keep track of callbacks. It is similar to + * the \ref spa_interfaces and typically used where an implementation allows + * for multiple external callback functions. For example, an implementation may + * use a hook list to implement signals with each caller using a hook to + * register callbacks to be invoked on those signals. * - * The hook list provides a way to keep track of hooks. + * The below (pseudo)code is a minimal example outlining the use of hooks: + * \code{.c} + * // the public interface + * struct bar_events { + * uint32_t version; + * void (*boom)(void *data, const char *msg); + * }; + * + * // private implementation + * struct party { + * struct spa_hook_list bar_list; + * }; + * + * void party_add_event_listener(struct party *p, struct spa_hook *listener, + * struct bar_events *events, void *data) + * { + * spa_hook_list_append(&p->bar_list, listener, events, data); + * } + * + * static void party_on(struct party *p) + * { + * spa_hook_list_call(&p->list, struct bar_events, + * boom, // function name + * 0 // hardcoded version, + * "party on, wayne"); + * } + * \endcode + * + * In the caller, the hooks can be used like this: + * \code{.c} + * static void boom_cb(void *data, const char *msg) { + * // data is userdata from main() + * printf("%s", msg); + * } + * + * static const struct bar_events { + * .boom = boom_cb, + * }; + * + * void main(void) { + * void *userdata = whatever; + * struct spa_hook hook; + * struct party *p = start_the_party(); + * + * party_add_event_listener(p, &hook, boom_cb, userdata); + * + * mainloop(); + * return 0; + * } + * + * \endcode */ /** - * \addtogroup spa_hook + * \addtogroup spa_hooks * \{ */ -/** A list of hooks */ +/** \struct spa_hook_list + * A list of hooks. This struct is primarily used by + * implementation that use multiple caller-provided \ref spa_hook. */ struct spa_hook_list { struct spa_list list; }; -/** A hook, contains the structure with functions and the data passed - * to the functions. */ +/** \struct spa_hook + * A hook, contains the structure with functions and the data passed + * to the functions. + * + * A hook should be treated as opaque by the caller. + */ struct spa_hook { struct spa_list link; struct spa_callbacks cb; @@ -241,7 +301,7 @@ struct spa_hook { void *priv; }; -/** Initialize a hook list */ +/** Initialize a hook list to the empty list*/ static inline void spa_hook_list_init(struct spa_hook_list *list) { spa_list_init(&list->list); @@ -280,6 +340,7 @@ static inline void spa_hook_remove(struct spa_hook *hook) hook->removed(hook); } +/** Remove all hooks from the list */ static inline void spa_hook_list_clean(struct spa_hook_list *list) { struct spa_hook *h; @@ -339,7 +400,16 @@ spa_hook_list_join(struct spa_hook_list *list, count; \ }) +/** + * Call the method named \a m for each element in list \a l. + * \a t specifies the type of the callback struct. + */ #define spa_hook_list_call(l,t,m,v,...) spa_hook_list_do_call(l,NULL,t,m,v,false,##__VA_ARGS__) +/** + * Call the method named \a m for each element in list \a l, stopping after + * the first invocation. + * \a t specifies the type of the callback struct. + */ #define spa_hook_list_call_once(l,t,m,v,...) spa_hook_list_do_call(l,NULL,t,m,v,true,##__VA_ARGS__) #define spa_hook_list_call_start(l,s,t,m,v,...) spa_hook_list_do_call(l,s,t,m,v,false,##__VA_ARGS__)