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task_server.ml
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task_server.ml
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(*
* Copyright (C) 2011 Citrix Systems Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation; version 2.1 only. with the special
* exception on linking described in file LICENSE.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*)
(**
* @group Xenops
*)
open Threadext
open Pervasiveext
open Listext
open Fun
type stringpair = string * string
module type INTERFACE = sig
val service_name : string
exception Does_not_exist of stringpair
exception Cancelled of string
module Task : sig
type id = string
type async_result
val rpc_of_async_result : async_result -> Rpc.t
val async_result_of_rpc : Rpc.t -> async_result
type completion_t = {
duration : float;
result : async_result option
}
type state =
| Pending of float
| Completed of completion_t
| Failed of Rpc.t
end
(* The following stuff comes from rpc-light.idl *)
module Exception : sig
type exnty
val rpc_of_exnty : exnty -> Rpc.t
end
val exnty_of_exn : exn -> Exception.exnty
val exn_of_exnty : Exception.exnty -> exn
exception Internal_error of string
end
module Task = functor (Interface : INTERFACE) -> struct
module D = Debug.Debugger(struct let name = Interface.service_name end)
open D
(* A task is associated with every running operation *)
type t = {
id: string; (* unique task id *)
ctime: float; (* created timestamp *)
debug_info: string; (* token sent by client *)
mutable state: Interface.Task.state; (* current completion state *)
mutable subtasks: (string * Interface.Task.state) list; (* one level of "subtasks" *)
f: t -> Interface.Task.async_result option; (* body of the function *)
tm: Mutex.t; (* protects cancelling state: *)
mutable cancelling: bool; (* set by cancel *)
mutable cancel: (unit -> unit) list; (* attempt to cancel [f] *)
}
module SMap = Map.Make(struct type t = string let compare = compare end)
(* Tasks are stored in an id -> t map *)
type tasks = {
tasks : t SMap.t ref;
m : Mutex.t;
c : Condition.t;
}
let empty () =
let tasks = ref SMap.empty in
let m = Mutex.create () in
let c = Condition.create () in
{ tasks; m; c }
(* [next_task_id ()] returns a fresh task id *)
let next_task_id =
let counter = ref 0 in
fun () ->
let result = string_of_int !counter in
incr counter;
result
(* [add dbg f] creates a fresh [t], registers and returns it *)
let add tasks dbg (f: t -> Interface.Task.async_result option) =
let t = {
id = next_task_id ();
ctime = Unix.gettimeofday ();
debug_info = dbg;
state = Interface.Task.Pending 0.;
subtasks = [];
f = f;
tm = Mutex.create ();
cancelling = false;
cancel = [];
} in
Mutex.execute tasks.m
(fun () ->
tasks.tasks := SMap.add t.id t !(tasks.tasks)
);
t
(* [run t] executes the task body, updating the fields of [t] *)
let run item =
try
let start = Unix.gettimeofday () in
let result = item.f item in
let duration = Unix.gettimeofday () -. start in
item.state <- Interface.Task.Completed { Interface.Task.duration; result }
with
| e ->
let e = e |> Interface.exnty_of_exn |> Interface.Exception.rpc_of_exnty in
debug "Caught exception while processing queue: %s" (e |> Jsonrpc.to_string);
debug "%s" (Printexc.get_backtrace ());
item.state <- Interface.Task.Failed e
let exists_locked tasks id = SMap.mem id !(tasks.tasks)
let find_locked tasks id =
if not (exists_locked tasks id) then raise (Interface.Does_not_exist("task", id));
SMap.find id !(tasks.tasks)
let with_subtask t name f =
let start = Unix.gettimeofday () in
try
t.subtasks <- (name, Interface.Task.Pending 0.) :: t.subtasks;
let result = f () in
let duration = Unix.gettimeofday () -. start in
t.subtasks <- List.replace_assoc name (Interface.Task.Completed {Interface.Task.duration; result=None}) t.subtasks;
result
with e ->
t.subtasks <- List.replace_assoc name (Interface.Task.Failed (Interface.Exception.rpc_of_exnty (Interface.exnty_of_exn (Interface.Internal_error (Printexc.to_string e))))) t.subtasks;
raise e
let list tasks =
Mutex.execute tasks.m
(fun () ->
SMap.bindings !(tasks.tasks) |> List.map snd
)
(* Remove the task from the id -> task mapping. NB any active thread will still continue. *)
let destroy tasks id =
Mutex.execute tasks.m
(fun () ->
tasks.tasks := SMap.remove id !(tasks.tasks)
)
let cancel tasks id =
let t = Mutex.execute tasks.m (fun () -> find_locked tasks id) in
let callbacks = Mutex.execute t.tm
(fun () ->
t.cancelling <- true;
t.cancel
) in
List.iter
(fun f ->
try
f ()
with e ->
debug "Task.cancel %s: ignore exception %s" id (Printexc.to_string e)
) callbacks
let raise_cancelled t = raise (Interface.Cancelled(t.id))
let check_cancelling t = if Mutex.execute t.tm (fun () -> t.cancelling) then raise_cancelled t
let with_cancel t cancel_fn f =
Mutex.execute t.tm (fun () -> t.cancel <- cancel_fn :: t.cancel);
finally
(fun () ->
check_cancelling t;
f ()
)
(fun () -> Mutex.execute t.tm (fun () -> t.cancel <- List.tl t.cancel))
end