-spec add_handler(EventMgrRef :: emgr_ref(), Handler :: handler(), Args :: term()) -> term().

Adds a new event handler to event manager EventMgrRef. The event manager calls Module:init/1 to initiate the event handler and its internal state.

Handler is the name of the callback module Module or a tuple {Module,Id}, where Id is any term. The {Module,Id} representation makes it possible to identify a specific event handler when many event handlers use the same callback module.

Args is any term that is passed as the argument to Module:init/1.

If Module:init/1 returns a correct value indicating successful completion, the event manager adds the event handler and this function returns ok. If Module:init/1 fails with Reason or returns {error,Reason}, the event handler is ignored and this function returns {'EXIT',Reason} or {error,Reason}, respectively.

-spec add_sup_handler(EventMgrRef :: emgr_ref(), Handler :: handler(), Args :: term()) -> term().

Adds a new event handler in the same way as add_handler/3, but also supervises the connection by linking the event handler and the calling process.

• If the calling process later terminates with Reason, the event manager deletes any supervised event handlers by calling Module:terminate/2, then calls Module:handle_info/2 for each remaining handler.
• If the event handler is deleted later, the event manager sends a message {gen_event_EXIT,Handler,Reason} to the calling process. Reason is one of the following:
  • normal, if the event handler has been removed because of a call to delete_handler/3, or remove_handler has been returned by a callback function (see below).
  • shutdown, if the event handler has been removed because the event manager is terminating.
  • {swapped,NewHandler,Pid}, if the process Pid has replaced the event handler with another event handler NewHandler using a call to swap_handler/3 or swap_sup_handler/3.
  • A term, if the event handler is removed because of an error. Which term depends on the error.

For a description of the arguments and return values, see add_handler/3.

-spec call(EventMgrRef :: emgr_ref(), Handler :: handler(), Request :: term()) -> term().

Equivalent to call(EventMgrRef, Handler, Request, 5000).

-spec call(EventMgrRef :: emgr_ref(), Handler :: handler(), Request :: term(), Timeout :: timeout()) ->
        term().

Makes a synchronous call to event handler Handler installed in event manager EventMgrRef by sending a request and waiting until a reply arrives or a time-out occurs. The event manager calls Module:handle_call/2 to handle the request.

Request is any term that is passed as one of the arguments to Module:handle_call/2.

Timeout is an integer greater than zero that specifies how many milliseconds to wait for a reply, or the atom infinity to wait indefinitely. Defaults to 5000. If no reply is received within the specified time, the function call fails.

The return value Reply is defined in the return value of Module:handle_call/2. If the specified event handler is not installed, the function returns {error,bad_module}. If the callback function fails with Reason or returns an unexpected value Term, this function returns {error,{'EXIT',Reason}} or {error,Term}, respectively.

When this call fails it exits the calling process. The exit term is on the form {Reason, Location} where Location = {gen_event,call,ArgList}. See gen_server:call/3 that has a description of relevant values for the Reason in the exit term.

-spec check_response(Msg, ReqId) -> Result
                  when
                      Msg :: term(),
                      ReqId :: request_id(),
                      Response ::
                          {reply, Reply :: term()} | {error, {Reason :: term(), emgr_ref()}},
                      Result :: Response | no_reply.

Check if Msg is a response corresponding to the request identifier ReqId. The request must have been made by send_request/3.

If Msg is a response corresponding to ReqId the response is returned; otherwise, no_reply is returned and no cleanup is done, and thus the function must be invoked repeatedly until a response is returned.

If the specified event handler is not installed, the function returns {error,bad_module}. If the callback function fails with Reason or returns an unexpected value Term, this function returns {error,{'EXIT',Reason}} or {error,Term}, respectively. If the event manager dies before or during the request this function returns {error,{Reason, EventMgrRef}}.

-spec check_response(Msg, ReqIdCollection, Delete) -> Result
                  when
                      Msg :: term(),
                      ReqIdCollection :: request_id_collection(),
                      Delete :: boolean(),
                      Response ::
                          {reply, Reply :: term()} | {error, {Reason :: term(), emgr_ref()}},
                      Result ::
                          {Response,
                           Label :: term(),
                           NewReqIdCollection :: request_id_collection()} |
                          no_request | no_reply.

Check if Msg is a response corresponding to a request identifier saved in ReqIdCollection. All request identifiers of ReqIdCollection must correspond to requests that have been made using send_request/3 or send_request/5, and all requests must have been made by the process calling this function.

The Label in the response equals the Label associated with the request identifier that the response corresponds to. The Label of a request identifier is associated when saving the request id in a request identifier collection, or when sending the request using send_request/5.

Compared to check_response/2, the returned result associated with a specific request identifier or an exception associated with a specific request identifier will be wrapped in a 3-tuple. The first element of this tuple equals the value that would have been produced by check_response/2, the second element equals the Label associated with the specific request identifier, and the third element NewReqIdCollection is a possibly modified request identifier collection.

If ReqIdCollection is empty, the atom no_request will be returned. If Msg does not correspond to any of the request identifiers in ReqIdCollection, the atom no_reply is returned.

If Delete equals true, the association with Label will have been deleted from ReqIdCollection in the resulting NewReqIdCollection. If Delete equals false, NewReqIdCollection will equal ReqIdCollection. Note that deleting an association is not for free and that a collection containing already handled requests can still be used by subsequent calls to check_response/3, receive_response/3, and wait_response/3. However, without deleting handled associations, the above calls will not be able to detect when there are no more outstanding requests to handle, so you will have to keep track of this some other way than relying on a no_request return. Note that if you pass a collection only containing associations of already handled or abandoned requests to check_response/3, it will always return no_reply.

-spec delete_handler(EventMgrRef :: emgr_ref(), Handler :: handler(), Args :: term()) -> term().

Deletes an event handler from event manager EventMgrRef. The event manager calls Module:terminate/2 to terminate the event handler.

Args is any term that is passed as one of the arguments to Module:terminate/2.

The return value is the return value of Module:terminate/2. If the specified event handler is not installed, the function returns {error,module_not_found}. If the callback function fails with Reason, the function returns {'EXIT',Reason}.

-spec notify(EventMgrRef :: emgr_ref(), Event :: term()) -> ok.

Sends an asynchronous event notification to event manager EventMgrRef. The event manager calls Module:handle_event/2 for each installed event handler to handle the event.

Event is any term that is passed as one of the arguments to Module:handle_event/2.

notify/1 does not fail even if the specified event manager does not exist, unless it is specified as Name.

-spec receive_response(ReqId, Timeout) -> Result
                    when
                        ReqId :: request_id(),
                        Timeout :: response_timeout(),
                        Response ::
                            {reply, Reply :: term()} | {error, {Reason :: term(), emgr_ref()}},
                        Result :: Response | timeout.

Receive a response corresponding to the request identifier ReqId. The request must have been made by send_request/3 to the gen_statem process. This function must be called from the same process from which send_request/3 was made.

Timeout specifies how long to wait for a response. If no response is received within the specified time, the function returns timeout. Assuming that the server executes on a node supporting aliases (introduced in OTP 24) the request will also be abandoned. That is, no response will be received after a timeout. Otherwise, a stray response might be received at a later time.

The return value Reply is defined in the return value of Module:handle_call/2.

If the specified event handler is not installed, the function returns {error,bad_module}. If the callback function fails with Reason or returns an unexpected value Term, this function returns {error,{'EXIT',Reason}} or {error,Term}, respectively. If the event manager dies before or during the request this function returns {error,{Reason, EventMgrRef}}.

The difference between wait_response/2 and receive_response/2 is that receive_response/2 abandons the request at timeout so that a potential future response is ignored, while wait_response/2 does not.

-spec receive_response(ReqIdCollection, Timeout, Delete) -> Result
                    when
                        ReqIdCollection :: request_id_collection(),
                        Timeout :: response_timeout(),
                        Delete :: boolean(),
                        Response ::
                            {reply, Reply :: term()} | {error, {Reason :: term(), emgr_ref()}},
                        Result ::
                            {Response,
                             Label :: term(),
                             NewReqIdCollection :: request_id_collection()} |
                            no_request | timeout.

Receive a response corresponding to a request identifier saved in ReqIdCollection. All request identifiers of ReqIdCollection must correspond to requests that have been made using send_request/3 or send_request/5, and all requests must have been made by the process calling this function.

The Label in the response equals the Label associated with the request identifier that the response corresponds to. The Label of a request identifier is associated when adding the request id in a request identifier collection, or when sending the request using send_request/5.

Compared to receive_response/2, the returned result associated with a specific request identifier will be wrapped in a 3-tuple. The first element of this tuple equals the value that would have been produced by receive_response/2, the second element equals the Label associated with the specific request identifier, and the third element NewReqIdCollection is a possibly modified request identifier collection.

If ReqIdCollection is empty, the atom no_request will be returned.

Timeout specifies how long to wait for a response. If no response is received within the specified time, the function returns timeout. Assuming that the server executes on a node supporting aliases (introduced in OTP 24) all requests identified by ReqIdCollection will also be abandoned. That is, no responses will be received after a timeout. Otherwise, stray responses might be received at a later time.

The difference between receive_response/3 and wait_response/3 is that receive_response/3 abandons the requests at timeout so that potential future responses are ignored, while wait_response/3 does not.

If Delete equals true, the association with Label will have been deleted from ReqIdCollection in the resulting NewReqIdCollection. If Delete equals false, NewReqIdCollection will equal ReqIdCollection. Note that deleting an association is not for free and that a collection containing already handled requests can still be used by subsequent calls to receive_response/3, check_response/3, and wait_response/3. However, without deleting handled associations, the above calls will not be able to detect when there are no more outstanding requests to handle, so you will have to keep track of this some other way than relying on a no_request return. Note that if you pass a collection only containing associations of already handled or abandoned requests to receive_response/3, it will always block until a timeout determined by Timeout is triggered.

-spec reqids_add(ReqId :: request_id(), Label :: term(), ReqIdCollection :: request_id_collection()) ->
              NewReqIdCollection :: request_id_collection().

Saves ReqId and associates a Label with the request identifier by adding this information to ReqIdCollection and returning the resulting request identifier collection.

-spec reqids_new() -> NewReqIdCollection :: request_id_collection().

Returns a new empty request identifier collection. A request identifier collection can be utilized in order the handle multiple outstanding requests.

Request identifiers of requests made by send_request/3 can be saved in a request identifier collection using reqids_add/3. Such a collection of request identifiers can later be used in order to get one response corresponding to a request in the collection by passing the collection as argument to receive_response/3, wait_response/3, or, check_response/3.

reqids_size/1 can be used to determine the amount of request identifiers in a request identifier collection.

-spec reqids_size(ReqIdCollection :: request_id_collection()) -> non_neg_integer().

Returns the amount of request identifiers saved in ReqIdCollection.

-spec reqids_to_list(ReqIdCollection :: request_id_collection()) ->
                  [{ReqId :: request_id(), Label :: term()}].

Returns a list of {ReqId, Label} tuples which corresponds to all request identifiers with their associated labels present in the ReqIdCollection collection.

-spec send_request(EventMgrRef :: emgr_ref(), Handler :: handler(), Request :: term()) ->
                ReqId :: request_id().

Sends an asynchronous call request Request to event handler Handler installed in the event manager identified by EventMgrRef and returns a request identifier ReqId. The return value ReqId shall later be used with receive_response/2, wait_response/2, or check_response/2 to fetch the actual result of the request.

Besides passing the request identifier directly to these functions, it can also be saved in a request identifier collection using reqids_add/3. Such a collection of request identifiers can later be used in order to get one response corresponding to a request in the collection by passing the collection as argument to receive_response/3, wait_response/3, or check_response/3. If you are about to save the request identifier in a request identifier collection, you may want to consider using send_request/5 instead.

The call gen_event:receive_response(gen_event:send_request(EventMgrRef, Handler, Request), Timeout) can be seen as equivalent to gen_event:call(EventMgrRef, Handler, Request, Timeout), ignoring the error handling.

The event manager calls Module:handle_call/2 to handle the request.

Request is any term that is passed as one of the arguments to Module:handle_call/2.

-spec send_request(EventMgrRef :: emgr_ref(),
             Handler :: handler(),
             Request :: term(),
             Label :: term(),
             ReqIdCollection :: request_id_collection()) ->
                NewReqIdCollection :: request_id_collection().

Sends an asynchronous call request Request to event handler Handler installed in the event manager identified by EventMgrRef. The Label will be associated with the request identifier of the operation and added to the returned request identifier collection NewReqIdCollection.

The collection can later be used in order to get one response corresponding to a request in the collection by passing the collection as argument to receive_response/3, wait_response/3, or check_response/3.

The same as calling gen_event:reqids_add(gen_event:send_request(EventMgrRef, Handler, Request), Label, ReqIdCollection), but calling send_request/5 is slightly more efficient.

-spec start() -> start_ret().

Equivalent to start([]).

-spec start(EventMgrNameOrOptions :: emgr_name() | options()) -> start_ret().

Creates a stand-alone event manager process, that is, an event manager that is not part of a supervision tree and thus has no supervisor.

For a description of the arguments and return values, see start_link/1.

-spec start(EventMgrName :: emgr_name(), Options :: options()) -> start_ret().

Creates a stand-alone event manager process, that is, an event manager that is not part of a supervision tree and thus has no supervisor.

For a description of the arguments and return values, see start_link/2.

-spec start_link() -> start_ret().

Equivalent to start_link([]).

-spec start_link(EventMgrNameOrOptions :: emgr_name() | options()) -> start_ret().

Creates an event manager process as part of a supervision tree.

If called with emgr_name/0, then it is equivalent to start(EventMgrName, []).

If called with options/0, then a nameless event manager is created using Options.

For a description of the arguments and return values, see start_link/2.

-spec start_link(EventMgrName :: emgr_name(), Options :: options()) -> start_ret().

Creates an event manager process as part of a supervision tree.

The function is to be called, directly or indirectly, by the supervisor. For example, it ensures that the event manager is linked to the caller (supervisor).

• If option {hibernate_after,HibernateAfterTimeout} is present, the gen_event process awaits any message for HibernateAfterTimeout milliseconds and if no message is received, the process goes into hibernation automatically (by calling proc_lib:hibernate/3).

If the event manager is successfully created, the function returns {ok,Pid}, where Pid is the pid of the event manager.

If a process with the specified EventMgrName exists already, the function returns {error,{already_started,OtherPid}}, where OtherPid is the pid of that process, and the event manager process exits with reason normal.

If the event manager fails to start within the specified start timeout {timeout,Time}, which is very unlikely since the start does not interact with other processes, the function returns {error,timeout} and the failed event manager is killed with exit(_, kill).

If start_link/1,2 returns {error,_}, the started event manager process has terminated. If an 'EXIT' message was delivered to the calling process (due to the process link), that message has been consumed.

Warning

Before OTP 26.0, if the started event manager failed to register its name, this founction could return {error,{already_started,OtherPid}} before the started event manager process had terminated so starting again might fail because the registered name was not yet unregistered, and an 'EXIT' message could arrive later to the process calling this function.

But if the start timed out, this function killed the started event manager process and returned {error,timeout}, and then the process link {'EXIT',Pid,killed} message was consumed.

The start was made synchronous in OTP 26.0 and the guarantee was implemented that no process link 'EXIT' message from a failed start will linger in the caller's inbox.

-spec start_monitor() -> start_mon_ret().

Equivalent to start_monitor([]).

-spec start_monitor(EventMgrNameOrOptions :: emgr_name() | options()) -> start_mon_ret().

Creates a stand-alone event manager process, that is, an event manager that is not part of a supervision tree (and thus has no supervisor) and atomically sets up a monitor to the newly created process.

For a description of the arguments and return values, see start_monitor/2 and start_link/1.

-spec start_monitor(EventMgtName :: emgr_name(), Options :: options()) -> start_mon_ret().

Creates a stand-alone event manager process, that is, an event manager that is not part of a supervision tree (and thus has no supervisor) and atomically sets up a monitor to the newly created process.

For a description of the arguments and return values, see start_link/2. Note that the return value on successful start differs from start_link/2. start_monitor/0,1,2 will return {ok,{Pid,Mon}} where Pid is the process identifier of the process, and Mon is a reference to the monitor set up to monitor the process. If the start is not successful, the caller will be blocked until the DOWN message has been received and removed from the message queue.

-spec stop(EventMgrRef :: emgr_ref()) -> ok.

Equivalent to stop(EventMgrRef, normal, infinity).

-spec stop(EventMgrRef :: emgr_ref(), Reason :: term(), Timeout :: timeout()) -> ok.

Orders event manager EventMgrRef to exit with the specifies Reason and waits for it to terminate. Before terminating, gen_event calls Module:terminate(stop,...) for each installed event handler.

The function returns ok if the event manager terminates with the expected reason. Any other reason than normal, shutdown, or {shutdown,Term} causes an error report to be issued using logger.

Timeout is an integer greater than zero that specifies how many milliseconds to wait for the event manager to terminate, or the atom infinity to wait indefinitely. If the event manager has not terminated within the specified time, the call exits the calling process with reason timeout.

If the process does not exist, the call exits the calling process with reason noproc, and with reason {nodedown,Node} if the connection fails to the remote Node where the server runs.

-spec swap_handler(EventMgrRef :: emgr_ref(),
             OldHandler :: {handler(), term()},
             NewHandler :: {handler(), term()}) ->
                ok | {error, term()}.

Replaces an old event handler with a new event handler in event manager EventMgrRef.

For a description of OldHandler and NewHandler, see add_handler/3.

First the old event handler OldHandler is deleted. The event manager calls OldModule:terminate(Args1, ...), where OldModule is the callback module of OldHandler, and collects the return value.

Then the new event handler NewHandler is added and initiated by calling NewModule:init({Args2,Term}), where NewModule is the callback module of OldHandler and Term is the return value of OldModule:terminate/2. This makes it possible to transfer information from OldHandler to NewHandler.

The new handler is added even if the the specified old event handler is not installed, in which case Term=error, or if OldModule:terminate/2 fails with Reason, in which case Term={'EXIT',Reason}. The old handler is deleted even if NewModule:init/1 fails.

If there was a supervised connection between OldHandler and a process Pid, there is a supervised connection between NewHandler and Pid instead.

If NewModule:init/1 returns a correct value, this function returns ok. If NewModule:init/1 fails with Reason or returns an unexpected value Term, this function returns {error,{'EXIT',Reason}} or {error,Term}, respectively.

-spec swap_sup_handler(EventMgrRef :: emgr_ref(),
                 OldHandler :: {handler(), term()},
                 NewHandler :: {handler(), term()}) ->
                    ok | {error, term()}.

Replaces an event handler in event manager EventMgrRef in the same way as swap_handler/3, but also supervises the connection between NewHandler and the calling process.

For a description of the arguments and return values, see swap_handler/3.

-spec sync_notify(EventMgrRef :: emgr_ref(), Event :: term()) -> ok.

Sends a synchronous event notification to event manager EventMgrRef. The event manager calls Module:handle_event/2 for each installed event handler to handle the event. This function will return ok after the event has been handled by all event handlers.

Event is any term that is passed as one of the arguments to Module:handle_event/2.

-spec wait_response(ReqId, WaitTime) -> Result
                 when
                     ReqId :: request_id(),
                     WaitTime :: response_timeout(),
                     Response ::
                         {reply, Reply :: term()} | {error, {Reason :: term(), emgr_ref()}},
                     Result :: Response | timeout.

Wait for a response corresponding to the request identifier ReqId. The request must have been made by send_request/3 to the gen_statem process. This function must be called from the same process from which send_request/3 was made.

WaitTime specifies how long to wait for a response. If no response is received within the specified time, the function returns timeout and no cleanup is done, and thus the function can be invoked repeatedly until a reply is returned.

The return value Reply is defined in the return value of Module:handle_call/2.

If the specified event handler is not installed, the function returns {error,bad_module}. If the callback function fails with Reason or returns an unexpected value Term, this function returns {error,{'EXIT',Reason}} or {error,Term}, respectively. If the event manager dies before or during the request this function returns {error,{Reason, EventMgrRef}}.

The difference between receive_response/2 and wait_response/2 is that receive_response/2 abandons the request at timeout so that a potential future response is ignored, while wait_response/2 does not.

-spec wait_response(ReqIdCollection, WaitTime, Delete) -> Result
                 when
                     ReqIdCollection :: request_id_collection(),
                     WaitTime :: response_timeout(),
                     Delete :: boolean(),
                     Response ::
                         {reply, Reply :: term()} | {error, {Reason :: term(), emgr_ref()}},
                     Result ::
                         {Response,
                          Label :: term(),
                          NewReqIdCollection :: request_id_collection()} |
                         no_request | timeout.

Wait for a response corresponding to a request identifier saved in ReqIdCollection. All request identifiers of ReqIdCollection must correspond to requests that have been made using send_request/3 or send_request/5, and all requests must have been made by the process calling this function.

The Label in the response equals the Label associated with the request identifier that the response corresponds to. The Label of a request identifier is associated when saving the request id in a request identifier collection, or when sending the request using send_request/5.

Compared to wait_response/2, the returned result associated with a specific request identifier or an exception associated with a specific request identifier will be wrapped in a 3-tuple. The first element of this tuple equals the value that would have been produced by wait_response/2, the second element equals the Label associated with the specific request identifier, and the third element NewReqIdCollection is a possibly modified request identifier collection.

If ReqIdCollection is empty, no_request will be returned. If no response is received before the WaitTime timeout has triggered, the atom timeout is returned. It is valid to continue waiting for a response as many times as needed up until a response has been received and completed by check_response(), receive_response(), or wait_response().

The difference between receive_response/3 and wait_response/3 is that receive_response/3 abandons requests at timeout so that potential future responses are ignored, while wait_response/3 does not.

If Delete equals true, the association with Label will have been deleted from ReqIdCollection in the resulting NewReqIdCollection. If Delete equals false, NewReqIdCollection will equal ReqIdCollection. Note that deleting an association is not for free and that a collection containing already handled requests can still be used by subsequent calls to wait_response/3, check_response/3, and receive_response/3. However, without deleting handled associations, the above calls will not be able to detect when there are no more outstanding requests to handle, so you will have to keep track of this some other way than relying on a no_request return. Note that if you pass a collection only containing associations of already handled or abandoned requests to wait_response/3, it will always block until a timeout determined by WaitTime is triggered and then return no_reply.

-spec which_handlers(EventMgrRef :: emgr_ref()) -> [handler()].

Returns a list of all event handlers installed in event manager EventMgrRef.

For a description of Handler, see add_handler/3.