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180 lines
8.9 KiB
C
180 lines
8.9 KiB
C
/* Copyright (c) 2016, The Tor Project, Inc. */
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/* See LICENSE for licensing information */
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/**
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* \file pubsub.h
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* \brief Macros to implement publish/subscribe abstractions.
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*
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* To use these macros, call DECLARE_PUBSUB_TOPIC() with an identifier to use
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* as your topic. Below, I'm going to assume you say DECLARE_PUBSUB_TOPIC(T).
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*
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* Doing this will declare the following types:
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* typedef struct T_event_data_t T_event_data_t; // you define this struct
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* typedef struct T_subscriber_data_t T_subscriber_data_t; // this one too.
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* typedef struct T_subscriber_t T_subscriber_t; // opaque
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* typedef int (*T_subscriber_fn_t)(T_event_data_t*, T_subscriber_data_t*);
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*
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* and it will declare the following functions:
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* const T_subscriber_t *T_subscribe(T_subscriber_fn_t,
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* T_subscriber_data_t *,
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* unsigned flags,
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* unsigned priority);
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* int T_unsubscribe(const T_subscriber_t *)
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*
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* Elsewhere you can say DECLARE_NOTIFY_PUBSUB_TOPIC(static, T), which
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* declares:
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*
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* static int T_notify(T_event_data_t *, unsigned notify_flags);
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* static void T_clear(void);
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*
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* And in some C file, you would define these functions with:
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* IMPLEMENT_PUBSUB_TOPIC(static, T).
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*
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* The implementations will be small typesafe wrappers over generic versions
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* of the above functions.
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*
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* To use the typesafe functions, you add any number of subscribers with
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* T_subscribe(). Each has an associated function pointer, data pointer,
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* and priority. Later, you can invoke T_notify() to declare that the
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* event has occurred. Each of the subscribers will be invoked once.
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**/
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#ifndef TOR_PUBSUB_H
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#define TOR_PUBSUB_H
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#include "torint.h"
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/**
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* Flag for T_subscribe: die with an assertion failure if the event
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* have ever been published before. Used when a subscriber must absolutely
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* never have missed an event.
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*/
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#define SUBSCRIBE_ATSTART (1u<<0)
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#define DECLARE_PUBSUB_STRUCT_TYPES(name) \
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/* You define this type. */ \
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typedef struct name ## _event_data_t name ## _event_data_t; \
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/* You define this type. */ \
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typedef struct name ## _subscriber_data_t name ## _subscriber_data_t;
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#define DECLARE_PUBSUB_TOPIC(name) \
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/* This type is opaque. */ \
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typedef struct name ## _subscriber_t name ## _subscriber_t; \
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/* You declare functions matching this type. */ \
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typedef int (*name ## _subscriber_fn_t)( \
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name ## _event_data_t *data, \
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name ## _subscriber_data_t *extra); \
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/* Call this function to subscribe to a topic. */ \
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const name ## _subscriber_t *name ## _subscribe( \
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name##_subscriber_fn_t subscriber, \
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name##_subscriber_data_t *extra_data, \
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unsigned flags, \
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unsigned priority); \
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/* Call this function to unsubscribe from a topic. */ \
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int name ## _unsubscribe(const name##_subscriber_t *s);
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#define DECLARE_NOTIFY_PUBSUB_TOPIC(linkage, name) \
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/* Call this function to notify all subscribers. Flags not yet used. */ \
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linkage int name ## _notify(name ## _event_data_t *data, unsigned flags); \
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/* Call this function to release storage held by the topic. */ \
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linkage void name ## _clear(void);
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/**
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* Type used to hold a generic function for a subscriber.
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*
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* [Yes, it is safe to cast to this, so long as we cast back to the original
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* type before calling. From C99: "A pointer to a function of one type may be
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* converted to a pointer to a function of another type and back again; the
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* result shall compare equal to the original pointer."]
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*/
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typedef int (*pubsub_subscriber_fn_t)(void *, void *);
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/**
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* Helper type to implement pubsub abstraction. Don't use this directly.
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* It represents a subscriber.
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*/
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typedef struct pubsub_subscriber_t {
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/** Function to invoke when the event triggers. */
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pubsub_subscriber_fn_t fn;
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/** Data associated with this subscriber. */
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void *subscriber_data;
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/** Priority for this subscriber. Low priorities happen first. */
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unsigned priority;
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/** Flags set on this subscriber. Not yet used.*/
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unsigned subscriber_flags;
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} pubsub_subscriber_t;
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/**
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* Helper type to implement pubsub abstraction. Don't use this directly.
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* It represents a topic, and keeps a record of subscribers.
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*/
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typedef struct pubsub_topic_t {
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/** List of subscribers to this topic. May be NULL. */
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struct smartlist_t *subscribers;
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/** Total number of times that pubsub_notify_() has ever been called on this
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* topic. */
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uint64_t n_events_fired;
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/** True iff we're running 'notify' on this topic, and shouldn't allow
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* any concurrent modifications or events. */
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unsigned locked;
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} pubsub_topic_t;
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const pubsub_subscriber_t *pubsub_subscribe_(pubsub_topic_t *topic,
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pubsub_subscriber_fn_t fn,
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void *subscriber_data,
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unsigned subscribe_flags,
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unsigned priority);
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int pubsub_unsubscribe_(pubsub_topic_t *topic, const pubsub_subscriber_t *sub);
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void pubsub_clear_(pubsub_topic_t *topic);
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typedef int (*pubsub_notify_fn_t)(pubsub_subscriber_t *subscriber,
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void *notify_data);
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int pubsub_notify_(pubsub_topic_t *topic, pubsub_notify_fn_t notify_fn,
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void *notify_data, unsigned notify_flags);
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#define IMPLEMENT_PUBSUB_TOPIC(notify_linkage, name) \
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static pubsub_topic_t name ## _topic_ = { NULL, 0, 0 }; \
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const name ## _subscriber_t * \
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name ## _subscribe(name##_subscriber_fn_t subscriber, \
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name##_subscriber_data_t *extra_data, \
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unsigned flags, \
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unsigned priority) \
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{ \
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const pubsub_subscriber_t *s; \
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s = pubsub_subscribe_(&name##_topic_, \
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(pubsub_subscriber_fn_t)subscriber, \
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extra_data, \
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flags, \
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priority); \
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return (const name##_subscriber_t *)s; \
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} \
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int \
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name ## _unsubscribe(const name##_subscriber_t *subscriber) \
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{ \
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return pubsub_unsubscribe_(&name##_topic_, \
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(const pubsub_subscriber_t *)subscriber); \
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} \
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static int \
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name##_call_the_notify_fn_(pubsub_subscriber_t *subscriber, \
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void *notify_data) \
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{ \
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name ## _subscriber_fn_t fn; \
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fn = (name ## _subscriber_fn_t) subscriber->fn; \
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return fn(notify_data, subscriber->subscriber_data); \
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} \
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notify_linkage int \
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name ## _notify(name ## _event_data_t *event_data, unsigned flags) \
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{ \
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return pubsub_notify_(&name##_topic_, \
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name##_call_the_notify_fn_, \
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event_data, \
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flags); \
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} \
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notify_linkage void \
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name ## _clear(void) \
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{ \
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pubsub_clear_(&name##_topic_); \
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}
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#endif /* TOR_PUBSUB_H */
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