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|
# Setting up the environment
```ocaml
# #require "eio.mock";;
```
```ocaml
open Eio.Std
let test label v =
traceln "%s: forcing..." label;
match Eio.Lazy.force v with
| v ->
Fiber.check ();
traceln "%s: %d" label v
| exception ex ->
traceln "%s: %a" label Fmt.exn ex;
Fiber.check ()
```
# Tests
Two fibers request the value. It's only computed once:
```ocaml
# Eio_mock.Backend.run @@ fun () ->
let v = Eio.Lazy.from_fun ~cancel:`Restart (fun () ->
traceln "calculating...";
Fiber.yield ();
traceln "complete";
42
) in
Fiber.both
(fun () -> test "a" v)
(fun () -> test "b" v)
;;
+a: forcing...
+calculating...
+b: forcing...
+complete
+a: 42
+b: 42
- : unit = ()
```
The calculation fails. It's still only performed once:
```ocaml
# Eio_mock.Backend.run @@ fun () ->
let v = Eio.Lazy.from_fun ~cancel:`Restart (fun () ->
traceln "calculating...";
Fiber.yield ();
failwith "failed";
) in
Fiber.both
(fun () -> test "a" v)
(fun () -> test "b" v)
;;
+a: forcing...
+calculating...
+b: forcing...
+a: Failure("failed")
+b: Failure("failed")
- : unit = ()
```
## Cancellation
The first fiber cancels. What happens depends on the cancel mode:
```ocaml
let test_cancel cancel =
Eio_mock.Backend.run @@ fun () ->
let v = Eio.Lazy.from_fun ~cancel (fun () ->
traceln "calculating...";
Fiber.yield ();
traceln "complete";
42
) in
Fiber.both
(fun () ->
let x =
Fiber.first
(fun () -> test "a" v; assert false)
(fun () -> 5)
in
traceln "a: %d" x
)
(fun () -> test "b" v)
;;
```
In record mode, the second fiber sees the cancelled exception:
```ocaml
# test_cancel `Record;;
+a: forcing...
+calculating...
+b: forcing...
+a: Cancelled: Eio__core__Fiber.Not_first
+b: Cancelled: Eio__core__Fiber.Not_first
+a: 5
- : unit = ()
```
In protect mode, the first calculation succeeds:
```ocaml
# test_cancel `Protect;;
+a: forcing...
+calculating...
+b: forcing...
+complete
+b: 42
+a: 5
- : unit = ()
```
In restart mode, the second fiber restarts the calculation:
```ocaml
# test_cancel `Restart;;
+a: forcing...
+calculating...
+b: forcing...
+a: Cancelled: Eio__core__Fiber.Not_first
+calculating...
+a: 5
+complete
+b: 42
- : unit = ()
```
|
