Module Task

module Task: sig .. end

High Level Interface to Command.
Since Carbon-20101201

Task

type 'a task

type 'a status =

`\|`	`Timeout`
`\|`	`Canceled`
`\|`	`Result of 'a`
`\|`	`Failed of exn`

val error : exn -> string

Extract error message form exception

val wait : 'a task -> 'a status

Blocks until termination.

val map : ('a -> 'b) -> 'a status -> 'b status

val pretty : (Format.formatter -> 'a -> unit) ->
       Format.formatter -> 'a status -> unit

Monadic Constructors

val nop : unit task

The task that immediately returns unit

val return : 'a -> 'a task

The task that immediately returns a result

val raised : exn -> 'a task

The task that immediately fails with an exception

val canceled : unit -> 'a task

The task that is immediately canceled

val failed : ('a, Format.formatter, unit, 'b task) Pervasives.format4 -> 'a

The task that immediately fails by raising a Failure exception. Typically: [let exit d : 'a task = failed "exit status %d" k]

val call : ('a -> 'b) -> 'a -> 'b task

The task that, when started, invokes a function and immediately returns the result.

val todo : (unit -> 'a task) -> 'a task

val status : 'a status -> 'a task

The task that immediately finishes with provided status

val bind : 'a task -> ('a status -> 'b task) -> 'b task

bind t k first runs t. Then, when t exit with status s, it starts task k s.

Remark: If t was cancelled, k s is still evaluated, but immediately canceled as well. This allows finally-like behaviors to be implemented. To evaluate k r only when t terminates normally, make use of the sequence operator.

val sequence : 'a task -> ('a -> 'b task) -> 'b task

sequence t k first runs t. If t terminates with Result r, then task k r is started. Otherwise, failure or cancelation of t is returned.

val job : 'a task -> unit task

val finally : 'a task -> ('a status -> unit) -> 'a task

finally t cb runs task t and always calls cb s when t exits with status s. Then s is returned. If the callback cb raises an exception, the returned status is emitted.

val callback : 'a task -> ('a status -> unit) -> unit task

Same as finally but the status of the task is discarded.

val (>>>) : 'a task -> ('a status -> 'b task) -> 'b task

bind infix.

val (>>=) : 'a task -> ('a -> 'b task) -> 'b task

sequence infix.

val (>>?) : 'a task -> ('a status -> unit) -> 'a task

finally infix.

val (>>!) : 'a task -> ('a status -> unit) -> unit task

callback infix.

Synchroneous Command

type mutex

val mutex : unit -> mutex

val sync : mutex -> (unit -> 'a task) -> 'a task

Schedules a task such that only one can run simultaneously for a given mutex.

System Command

val command : ?timeout:int ->
       ?time:float Pervasives.ref ->
       ?stdout:Buffer.t ->
       ?stderr:Buffer.t -> string -> string array -> int task

Immediately launch a system-process. Default timeout is 0, which means no-timeout at all. Standard outputs are discarded unless optional buffers are provided. To make the task start later, simply use todo (command ...).

Shared Tasks

When two tasks A and B share a common sub-task S, cancelling A will make B fail either. To prevent this, it is necessary to make S shareable and to use two distinct instances of S in A and B.

Shared tasks manage the number of their instance and actually run or cancel a unique task on demand. In particular, shared tasks can be canceled and re-started later.

type 'a shared

Shareable tasks.

val shared : descr:string -> retry:bool -> (unit -> 'a task) -> 'a shared

Build a shareable task. The build function is called whenever a new instance is required but no shared instance task is actually running. Interrupted tasks (by Cancel or Timeout) are retried for further instances. If the task failed, it can be re-launch if retry is true. Otherwize, further instances will return Failed status.

val share : 'a shared -> 'a task

New instance of shared task.

Task Server

type server

type thread

val thread : 'a task -> thread

val cancel : thread -> unit

val run : thread -> unit

Runs one single task in the background. Typically using on_idle.

val server : ?stages:int -> ?procs:int -> unit -> server

Creates a server of commands.

stages : number of queues in the server. Stage 0 tasks are issued first. Default is 1.

procs : maximum number of running tasks. Default is 4.

val spawn : server -> ?stage:int -> thread -> unit

Schedules a task on the server. The task is not immediately started.

val launch : server -> unit

Starts the server if not running yet

val cancel_all : server -> unit

Cancel all scheduled tasks

val set_procs : server -> int -> unit

Adjusts the maximum number of running process.

val on_server_activity : server -> (unit -> unit) -> unit

Idle server callback

val on_server_start : server -> (unit -> unit) -> unit

On-start server callback

val on_server_stop : server -> (unit -> unit) -> unit

On-stop server callback

val on_server_wait : server -> (unit -> unit) -> unit

On-wait server callback (all tasks are scheduled)

val scheduled : server -> int

Number of scheduled process

val terminated : server -> int

Number of terminated process

val waiting : server -> int option

All task scheduled and server is waiting for termination

GUI Configuration

val on_idle : ((unit -> bool) -> unit) Pervasives.ref

Typically modified by GUI. !on_idle f should repeatedly calls f until it returns false. Default implementation rely on Unix.sleep 1 and Db.progress. See also Gtk_helper module implementation.