Eliom_comet.Channel(3) Basic primitives needed for server push.


Module Eliom_comet.Channel


Module Channel
 :  sig end

Basic primitives needed for server push.

type 'a t

v t is the type of server-to-client communication channels transporting data of type v

type comet_scope = [ `Client_process of Eliom_common.scope_name | `Site ]

val create : ?scope:[< comet_scope ] -> ?name:string -> ?size:int -> 'a Lwt_stream.t -> 'a t

create s returns a channel sending values from s .

There are two kind of channels created depending on the given scope (defaults to Eliom_common.comet_client_process ).

With scope Eliom_common.site all users knowing the name of the channel can access it. Only one message queue is created: it is what we call a stateless channel in the sense that the memory used by the channel does not depend on the number of users. The channel can be reclaimed by the GC when there is no more reference to it. The buffer channel has a limited buffer of size size (default: 1000). If the client requests too old messages, exception Eliom_coment.Channel_full will be raised (on client side).

With a scope of level Eliom_common.client_process_scope the channel can only be accessed by the user who created it. It can only be created when client application data is available. The eliom service created to communicate with the client is only available in the scope of the client process. To avoid memory leak when the client do not read sent data, the channel has a limited size . When a channel is full, no data can be read from it anymore.

A channel can be used only once on client side. To be able to receive the same data multiple times on client side, use create (Lwt_stream.clone s) every time.

To enforce the limit on the buffer size, the data is read into stream as soon as possible: If you want a channel that reads data on the stream only when the client requests it, use create_unlimited instead, but be careful of memory leaks.

val create_unlimited : ?scope:Eliom_common.client_process_scope -> ?name:string -> 'a Lwt_stream.t -> 'a t

create_unlimited s creates a channel which does not read immediately on the stream. It is read only when the client requests it: use it if the data you send depends on the time of the request (for instance the number of unread mails). Be careful, the size of this stream is not limited: if the size of the stream increases and your clients don't read it, you may have memory leaks.

val create_newest : ?name:string -> 'a Lwt_stream.t -> 'a t

create_newest s is similar to create ~scope:Eliom_common.site s but only the last message is returned to the client.

val external_channel : ?history:int -> ?newest:bool -> prefix:string -> name:string -> unit -> 'a t

external_channel ~prefix ~name () declares an external channel. The channel was created by an instance of Eliom serving the prefix prefix (the prefix configured in the <site> tag of the configuration file). The channel was named by name . Both servers must run the exact same version of Eliom.

The optional newest parameters tells whether the channel is a new one. If the channel is not new, history is the maximum number of messages retrieved at the first request. The default is 1 .

val wait_timeout : ?scope:Eliom_common.client_process_scope -> float -> unit Lwt.t

wait_timeout ~scope time waits for a period of inactivity of length time in the scope . Only activity on stateful channels is taken into accounts.

The default scope is Eliom_common.comet_client_process .