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Diffstat (limited to 'src/lib/pubsub/pubsub_macros.h')
| -rw-r--r-- | src/lib/pubsub/pubsub_macros.h | 373 |
1 files changed, 373 insertions, 0 deletions
diff --git a/src/lib/pubsub/pubsub_macros.h b/src/lib/pubsub/pubsub_macros.h new file mode 100644 index 0000000000..e5ffbe501a --- /dev/null +++ b/src/lib/pubsub/pubsub_macros.h @@ -0,0 +1,373 @@ +/* Copyright (c) 2001, Matej Pfajfar. + * Copyright (c) 2001-2004, Roger Dingledine. + * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson. + * Copyright (c) 2007-2020, The Tor Project, Inc. */ +/* See LICENSE for licensing information */ + +/** + * \file pubsub_macros.h + * \brief Macros to help with the publish/subscribe dispatch API. + * + * The dispatch API allows different subsystems of Tor to communicate with + * another asynchronously via a shared "message" system. Some subsystems + * declare that they publish a given message, and others declare that they + * subscribe to it. Both subsystems depend on the message, but not upon one + * another. + * + * To declare a message, use DECLARE_MESSAGE() (for messages that take their + * data as a pointer) or DECLARE_MESSAGE_INT() (for messages that take their + * data as an integer. For example, you might say + * + * DECLARE_MESSAGE(new_circuit, circ, circuit_handle_t *); + * or + * DECLARE_MESSAGE_INT(shutdown_requested, boolean, bool); + * + * Every message has a unique name, a "type name" that the dispatch system + * uses to manage associated data, and a C type name. You'll want to put + * these declarations in a header, to be included by all publishers and all + * subscribers. + * + * When a subsystem wants to publish a message, it uses DECLARE_PUBLISH() at + * file scope to create necessary static functions. Then, in its subsystem + * initialization (in the "bind to dispatcher" callback) (TODO: name this + * properly!), it calls DISPATCH_ADD_PUB() to tell the dispatcher about its + * intent to publish. When it actually wants to publish, it uses the + * PUBLISH() macro. For example: + * + * // At file scope + * DECLARE_PUBLISH(shutdown_requested); + * + * static void bind_to_dispatcher(pubsub_connector_t *con) + * { + * DISPATCH_ADD_PUB(con, mainchannel, shutdown_requested); + * } + * + * // somewhere in a function + * { + * PUBLISH(shutdown_requested, true); + * } + * + * When a subsystem wants to subscribe to a message, it uses + * DECLARE_SUBSCRIBE() at file scope to declare static functions. It must + * declare a hook function that receives the message type. Then, in its "bind + * to dispatcher" function, it calls DISPATCHER_ADD_SUB() to tell the + * dispatcher about its intent to subscribe. When another module publishes + * the message, the dispatcher will call the provided hook function. + * + * // At file scope. The first argument is the message that you're + * // subscribing to; the second argument is the hook function to declare. + * DECLARE_SUBSCRIBE(shutdown_requested, on_shutdown_req_cb); + * + * // You need to declare this function. + * static void on_shutdown_req_cb(const msg_t *msg, + * bool value) + * { + * // (do something here.) + * } + * + * static void bind_to_dispatcher(pubsub_connector_t *con) + * { + * DISPATCH_ADD_SUB(con, mainchannel, shutdown_requested); + * } + * + * Where did these types come from? Somewhere in the code, you need to call + * DISPATCH_REGISTER_TYPE() to make sure that the dispatcher can manage the + * message auxiliary data. It associates a vtbl-like structure with the + * type name, so that the dispatcher knows how to manipulate the type you're + * giving it. + * + * For example, the "boolean" type we're using above could be defined as: + * + * static char *boolean_fmt(msg_aux_data_t d) + * { + * // This is used for debugging and dumping messages. + * if (d.u64) + * return tor_strdup("true"); + * else + * return tor_strdup("false"); + * } + * + * static void boolean_free(msg_aux_data_t d) + * { + * // We don't actually need to do anything to free a boolean. + * // We could use "NULL" instead of this function, but I'm including + * // it as an example. + * } + * + * static void bind_to_dispatcher(pubsub_connector_t *con) + * { + * dispatch_typefns_t boolean_fns = { + * .fmt_fn = boolean_fmt, + * .free_fn = boolean_free, + * }; + * DISPATCH_REGISTER_TYPE(con, boolean, &boolean_fns); + * } + * + * + * + * So, how does this all work? (You can stop reading here, unless you're + * debugging something.) + * + * When you declare a message in a header with DECLARE_MESSAGE() or + * DECLARE_MESSAGE_INT(), it creates five things: + * + * * two typedefs for the message argument (constant and non-constant + * variants). + * * a constant string to hold the declared message type name + * * two inline functions, to coerce the message argument type to and from + * a "msg_aux_data_t" union. + * + * All of these declarations have names based on the message name. + * + * Later, when you say DECLARE_PUBLISH() or DECLARE_SUBSCRIBE(), we use the + * elements defined by DECLARE_MESSAGE() to make sure that the publish + * function takes the correct argument type, and that the subscription hook is + * declared with the right argument type. + **/ + +#ifndef TOR_DISPATCH_MSG_H +#define TOR_DISPATCH_MSG_H + +#include "lib/cc/compat_compiler.h" +#include "lib/dispatch/dispatch_naming.h" +#include "lib/pubsub/pub_binding_st.h" +#include "lib/pubsub/pubsub_connect.h" +#include "lib/pubsub/pubsub_flags.h" +#include "lib/pubsub/pubsub_publish.h" + +/* Implemenation notes: + * + * For a messagename "foo", the DECLARE_MESSAGE*() macros must declare: + * + * msg_arg_type__foo -- a typedef for the argument type of the foo message. + * msg_arg_consttype__foo -- a typedef for the const argument type of the + * foo message. + * msg_arg_name__foo[] -- a static string constant holding the unique + * identifier for the type of the foo message. + * msg_arg_get__foo() -- an inline function taking a msg_aux_data_t and + * returning the C data type. + * msg_arg_set__foo() -- an inline function taking a msg_aux_data_t and + * the C type, setting the msg_aux_data_t to hold the C type. + * + * For a messagename "foo", the DECLARE_PUBLISH() macro must declare: + * + * pub_binding__foo -- A static pub_binding_t object used to send messages + * from this module. + * publish_fn__foo -- A function taking an argument of the appropriate + * C type, to be invoked by PUBLISH(). + * + * For a messagename "foo", the DECLARE_SUBSCRIBE() macro must declare: + * + * hookfn -- A user-provided function name, with the correct signature. + * recv_fn__foo -- A wrapper callback that takes a msg_t *, and calls + * hookfn with the appropriate arguments. + */ + +/** Macro to declare common elements shared by DECLARE_MESSAGE and + * DECLARE_MESSAGE_INT. Don't call this directly. + * + * Note that the "msg_arg_name" string constant is defined in each + * translation unit. This might be undesirable; we can tweak it in the + * future if need be. + */ +#define DECLARE_MESSAGE_COMMON__(messagename, typename, c_type) \ + typedef c_type msg_arg_type__ ##messagename; \ + typedef const c_type msg_arg_consttype__ ##messagename; \ + ATTR_UNUSED static const char msg_arg_name__ ##messagename[] = # typename; + +/** + * Use this macro in a header to declare the existence of a given message, + * taking a pointer as auxiliary data. + * + * "messagename" is a unique identifier for the message; it must be a valid + * C identifier. + * + * "typename" is a unique identifier for the type of the auxiliary data. + * It needs to be defined somewhere in Tor, using + * "DISPATCH_REGISTER_TYPE." + * + * "c_ptr_type" is a C pointer type (like "char *" or "struct foo *"). + * The "*" needs to be included. + */ +#define DECLARE_MESSAGE(messagename, typename, c_ptr_type) \ + DECLARE_MESSAGE_COMMON__(messagename, typename, c_ptr_type) \ + ATTR_UNUSED static inline c_ptr_type \ + msg_arg_get__ ##messagename(msg_aux_data_t m) \ + { \ + return m.ptr; \ + } \ + ATTR_UNUSED static inline void \ + msg_arg_set__ ##messagename(msg_aux_data_t *m, c_ptr_type v) \ + { \ + m->ptr = v; \ + } \ + EAT_SEMICOLON + +/** + * Use this macro in a header to declare the existence of a given message, + * taking an integer as auxiliary data. + * + * "messagename" is a unique identifier for the message; it must be a valid + * C identifier. + * + * "typename" is a unique identifier for the type of the auxiliary data. It + * needs to be defined somewhere in Tor, using "DISPATCH_REGISTER_TYPE." + * + * "c_type" is a C integer type, like "int" or "bool". It needs to fit inside + * a uint64_t. + */ +#define DECLARE_MESSAGE_INT(messagename, typename, c_type) \ + DECLARE_MESSAGE_COMMON__(messagename, typename, c_type) \ + ATTR_UNUSED static inline c_type \ + msg_arg_get__ ##messagename(msg_aux_data_t m) \ + { \ + return (c_type)m.u64; \ + } \ + ATTR_UNUSED static inline void \ + msg_arg_set__ ##messagename(msg_aux_data_t *m, c_type v) \ + { \ + m->u64 = (uint64_t)v; \ + } \ + EAT_SEMICOLON + +/** + * Use this macro inside a C module declare that we'll be publishing a given + * message type from within this module. + * + * It creates necessary functions and wrappers to publish a message whose + * unique identifier is "messagename". + * + * Before you use this, you need to include the header where DECLARE_MESSAGE*() + * was used for this message. + * + * You can only use this once per message in each subsystem. + */ +#define DECLARE_PUBLISH(messagename) \ + static pub_binding_t pub_binding__ ##messagename; \ + static void \ + publish_fn__ ##messagename(msg_arg_type__ ##messagename arg) \ + { \ + msg_aux_data_t data; \ + msg_arg_set__ ##messagename(&data, arg); \ + pubsub_pub_(&pub_binding__ ##messagename, data); \ + } \ + EAT_SEMICOLON + +/** + * Use this macro inside a C file to declare that we're subscribing to a + * given message and associating it with a given "hook function". It + * declares the hook function static, and helps with strong typing. + * + * Before you use this, you need to include the header where + * DECLARE_MESSAGE*() was used for the message whose unique identifier is + * "messagename". + * + * You will need to define a function with the name that you provide for + * "hookfn". The type of this function will be: + * static void hookfn(const msg_t *, const c_type) + * where c_type is the c type that you declared in the header. + * + * You can only use this once per message in each subsystem. + */ +#define DECLARE_SUBSCRIBE(messagename, hookfn) \ + static void hookfn(const msg_t *, \ + const msg_arg_consttype__ ##messagename); \ + static void recv_fn__ ## messagename(const msg_t *m) \ + { \ + msg_arg_type__ ## messagename arg; \ + arg = msg_arg_get__ ##messagename(m->aux_data__); \ + hookfn(m, arg); \ + } \ + EAT_SEMICOLON + +/** + * Add a fake use of the publish function for 'messagename', so that + * the compiler does not call it unused. + */ +#define DISPATCH__FAKE_USE_OF_PUBFN_(messagename) \ + ( 0 ? (publish_fn__ ##messagename((msg_arg_type__##messagename)0), 1) \ + : 1) + +/** + * This macro is for internal use. It backs DISPATCH_ADD_PUB*() + */ +#define DISPATCH_ADD_PUB_(connector, channel, messagename, flags) \ + ( \ + DISPATCH__FAKE_USE_OF_PUBFN_(messagename), \ + pubsub_add_pub_((connector), \ + &pub_binding__ ##messagename, \ + get_channel_id(# channel), \ + get_message_id(# messagename), \ + get_msg_type_id(msg_arg_name__ ## messagename), \ + (flags), \ + __FILE__, \ + __LINE__) \ + ) + +/** + * Use a given connector and channel name to declare that this subsystem will + * publish a given message type. + * + * Call this macro from within the add_subscriptions() function of a module. + */ +#define DISPATCH_ADD_PUB(connector, channel, messagename) \ + DISPATCH_ADD_PUB_(connector, channel, messagename, 0) + +/** + * Use a given connector and channel name to declare that this subsystem will + * publish a given message type, and that no other subsystem is allowed to. + * + * Call this macro from within the add_subscriptions() function of a module. + */ +#define DISPATCH_ADD_PUB_EXCL(connector, channel, messagename) \ + DISPATCH_ADD_PUB_(connector, channel, messagename, DISP_FLAG_EXCL) + +/** + * This macro is for internal use. It backs DISPATCH_ADD_SUB*() + */ +#define DISPATCH_ADD_SUB_(connector, channel, messagename, flags) \ + pubsub_add_sub_((connector), \ + recv_fn__ ##messagename, \ + get_channel_id(#channel), \ + get_message_id(# messagename), \ + get_msg_type_id(msg_arg_name__ ##messagename), \ + (flags), \ + __FILE__, \ + __LINE__) +/** + * Use a given connector and channel name to declare that this subsystem will + * receive a given message type. + * + * Call this macro from within the add_subscriptions() function of a module. + */ +#define DISPATCH_ADD_SUB(connector, channel, messagename) \ + DISPATCH_ADD_SUB_(connector, channel, messagename, 0) +/** + * Use a given connector and channel name to declare that this subsystem will + * receive a given message type, and that no other subsystem is allowed to do + * so. + * + * Call this macro from within the add_subscriptions() function of a module. + */ +#define DISPATCH_ADD_SUB_EXCL(connector, channel, messagename) \ + DISPATCH_ADD_SUB_(connector, channel, messagename, DISP_FLAG_EXCL) + +/** + * Publish a given message with a given argument. (Takes ownership of the + * argument if it is a pointer.) + */ +#define PUBLISH(messagename, arg) \ + publish_fn__ ##messagename(arg) + +/** + * Use a given connector to declare that the functions to be used to manipuate + * a certain C type. + **/ +#define DISPATCH_REGISTER_TYPE(con, type, fns) \ + pubsub_connector_register_type_((con), \ + get_msg_type_id(#type), \ + (fns), \ + __FILE__, \ + __LINE__) + +#endif /* !defined(TOR_DISPATCH_MSG_H) */ |