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

Add a new event handler to an event manager.

The new event handler is added 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().

Add a new event handler to an event manager, supervised.

The new event handler is added as for add_handler/3, but the event manager 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, through a call to swap_handler/3 or swap_sup_handler/3.
  • Other term/0, 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().

Make a synchronous call to an event handler.

The call is sent to 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 a received message is a request response.

Check if Msg is a response corresponding to the request identifier ReqId. The request must have been made by send_request/3, and by the same process calling this function.

If Msg is a response corresponding to ReqId the response is returned in Reply. Otherwise this function returns no_reply and no cleanup is done. Thus this 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 has died before this function is called, that is; Msg reports the server's death, this function returns {error,{Reason, EventMgrRef}} where Reason is the exit reason.

-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 a received message is a request response in a collection.

Check if Msg is a response corresponding to a request identifier stored 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 is the Label associated with the request identifier that the response corresponds to. The Label of a request identifier is associated when storing the request id in a collection, or when sending the request using send_request/5.

Compared to check_response/2, the returned result or exception associated with a specific request identifier will be wrapped in a 3-tuple {Response, Label, NewReqIdCollection}. Response is the value that would have been produced by check_response/2, Label is the value associated with the specific request identifier and NewReqIdCollection is a possibly modified request identifier collection.

If ReqIdCollection is empty, no_request will be returned.

If Msg does not correspond to any of the request identifiers in ReqIdCollection, no_reply is returned.

If Delete is true, the association with Label has been deleted from ReqIdCollection in the resulting NewReqIdCollection. If Delete is 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 an event manager.

This function deletes event handler 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.

Send an asynchronous event notification to an event manager.

The event is sent to EventMgrRef, that 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 request response.

Receive a response corresponding to the request identifier ReqId. The request must have been made by send_request/3, and it must have been made from the same process calling this function.

Timeout specifies how long to wait for a response. If no response is received within the specified time, this 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, this 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 time-out 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 request response in a collection.

Receive a response 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 is 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 to a collection, or when sending the request using send_request/5.

Compared to receive_response/2, the returned result or exception associated with a specific request identifier will be wrapped in a 3-tuple {Response, Label, NewReqIdCollection}. Response is the value that would have been produced by receive_response/2, Label is the value associated with the specific request identifier and NewReqIdCollection is a possibly modified request identifier collection.

If ReqIdCollection is empty, 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 time-out. 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 time-out so that potential future responses are ignored, while wait_response/3 does not.

If Delete is true, the association with Label is deleted from ReqIdCollection in the resulting NewReqIdCollection. If Delete is 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 Timeout expires and then return timeout.

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

Store a request identifier in a colletion.

Stores 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().

Create an empty request identifier collection.

Returns a new empty request identifier collection. A request identifier collection can be utilized to 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 number of request identifiers in a collection.

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

Returns the number of request identifiers in ReqIdCollection.

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

Convert a request identifier collection to a list.

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

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

Send an asynchronous call request to an event handler.

This function sends the call request Request to the 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 stored 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 store the request identifier in a collection, you may want to consider using send_request/5 instead.

The calls 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 may be any term and 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().

Send an asynchronous call request to an event handler, storing it in a request identifier collection.

This function sends the call request Request to the 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 slightly more efficient.

-spec start() -> start_ret().

Equivalent to start([]).

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

Create a stand-alone event manager process, possibly nameless.

Equivalent to start(EventMgrName, Options).

With argument EventMgrName, Options is [].

With argument Options a nameless event manager is created.

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

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

Create a stand-alone event manager process.

The created event manager process 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(EventMgrName :: emgr_name()) -> start_ret();
                (Options :: options()) -> start_ret().

Create an event manager process as part of a supervision tree, possibly nameless.

Equivalent to start_link(EventMgrName, Options).

With argument EventMgrName, Options is [].

With argument Options a nameless event manager is created.

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

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

Create 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/0 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 a 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, monitored, possibly nameless.

Equivalent to start_monitor(EventMgrName, Options).

With argument EventMgrName, Options is [].

With argument Options a nameless event manager is created.

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, monitored.

The created event manager process is not part of a supervision tree and thus has no supervisor. A monitor is atomically set up to the newly created process.

For a description of the arguments and return values, see start_link/2. Note that the return value for a 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.

Stop an event manager.

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()}.

Replace an event handler.

This function replaces an 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 NewHandler, 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()}.

Replace an event handler, and supervise it.

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.

Send a synchronous event notification to an event manager.

The event is sent to EventMgrRef that callsr 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 request resonse.

Wait for the response to the request identifier ReqId. The request must have been made by send_request/3, from the same process that called send_request/3.

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, 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 any request response in a collection.

Wait for a response in a 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 is 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 to a collection, or when sending the request using send_request/5.

Compared to wait_response/2, the returned result or exception associated with a specific request identifier will be wrapped in a 3-tuple {Response, Label, NewReqIdCollection}. Response is the value that would have been produced by wait_response/2, Label is the value associated with the specific request identifier and 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 has expired, 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 time-out so that potential future responses are ignored, while wait_response/3 does not.

If Delete is true, the association with Label has been deleted from ReqIdCollection in the resulting NewReqIdCollection. If Delete isfalse, 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 this function, it will always block until WaitTime expires and then return timeout.

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

Return all event handlers in an event manager.

This function returns a list of all event handlers installed in event manager EventMgrRef.

For a description of Handler, see add_handler/3.