rust/src/libstd/future.rs

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// NB: transitionary, de-mode-ing.
// tjc: allowing deprecated modes due to function issue.
// can re-forbid them after snapshot
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#[forbid(deprecated_pattern)];
/*!
* A type representing values that may be computed concurrently and
* operations for working with them.
*
* # Example
*
* ~~~
* let delayed_fib = future::spawn {|| fib(5000) };
* make_a_sandwich();
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* io::println(fmt!("fib(5000) = %?", delayed_fib.get()))
* ~~~
*/
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use either::Either;
use pipes::{recv, oneshot, ChanOne, PortOne, send_one, recv_one};
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use cast::copy_lifetime;
#[doc = "The future type"]
pub struct Future<A> {
/*priv*/ mut state: FutureState<A>,
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}
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// FIXME(#2829) -- futures should not be copyable, because they close
// over fn~'s that have pipes and so forth within!
impl<A> Future<A> : Drop {
fn finalize() {}
}
priv enum FutureState<A> {
Pending(fn~() -> A),
Evaluating,
Forced(~A)
}
/// Methods on the `future` type
impl<A:Copy> Future<A> {
fn get() -> A {
//! Get the value of the future
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get(&self)
}
}
impl<A> Future<A> {
fn get_ref(&self) -> &self/A {
get_ref(self)
}
fn with<B>(blk: fn(&A) -> B) -> B {
//! Work with the value without copying it
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with(&self, blk)
}
}
pub fn from_value<A>(val: A) -> Future<A> {
/*!
* Create a future from a value
*
* The value is immediately available and calling `get` later will
* not block.
*/
Future {state: Forced(~(move val))}
}
pub fn from_port<A:Send>(port: PortOne<A>) ->
Future<A> {
/*!
* Create a future from a port
*
* The first time that the value is requested the task will block
* waiting for the result to be received on the port.
*/
let port = ~mut Some(move port);
do from_fn |move port| {
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let mut port_ = None;
port_ <-> *port;
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let port = option::unwrap(move port_);
match recv(move port) {
oneshot::send(move data) => move data
}
}
}
pub fn from_fn<A>(f: ~fn() -> A) -> Future<A> {
/*!
* Create a future from a function.
*
* The first time that the value is requested it will be retreived by
* calling the function. Note that this function is a local
* function. It is not spawned into another task.
*/
Future {state: Pending(move f)}
}
pub fn spawn<A:Send>(blk: fn~() -> A) -> Future<A> {
/*!
* Create a future from a unique closure.
*
* The closure will be run in a new task and its result used as the
* value of the future.
*/
let (chan, port) = oneshot::init();
let chan = ~mut Some(move chan);
do task::spawn |move blk, move chan| {
let chan = option::swap_unwrap(&mut *chan);
send_one(move chan, blk());
}
return from_port(move port);
}
pub fn get_ref<A>(future: &r/Future<A>) -> &r/A {
/*!
* Executes the future's closure and then returns a borrowed
* pointer to the result. The borrowed pointer lasts as long as
* the future.
*/
// The unsafety here is to hide the aliases from borrowck, which
// would otherwise be concerned that someone might reassign
// `future.state` and cause the value of the future to be freed.
// But *we* know that once `future.state` is `Forced()` it will
// never become "unforced"---so we can safely return a pointer
// into the interior of the Forced() variant which will last as
// long as the future itself.
match future.state {
Forced(ref v) => { // v here has type &A, but with a shorter lifetime.
return unsafe{ copy_lifetime(future, &**v) }; // ...extend it.
}
Evaluating => {
fail ~"Recursive forcing of future!";
}
Pending(_) => {}
}
let mut state = Evaluating;
state <-> future.state;
match move state {
Forced(_) | Evaluating => {
fail ~"Logic error.";
}
Pending(move f) => {
future.state = Forced(~f());
return get_ref(future);
}
}
}
pub fn get<A:Copy>(future: &Future<A>) -> A {
//! Get the value of the future
*get_ref(future)
}
pub fn with<A,B>(future: &Future<A>, blk: fn(&A) -> B) -> B {
//! Work with the value without copying it
blk(get_ref(future))
}
#[allow(non_implicitly_copyable_typarams)]
pub mod test {
#[test]
pub fn test_from_value() {
let f = from_value(~"snail");
assert get(&f) == ~"snail";
}
#[test]
pub fn test_from_port() {
let (ch, po) = oneshot::init();
send_one(move ch, ~"whale");
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let f = from_port(move po);
assert get(&f) == ~"whale";
}
#[test]
pub fn test_from_fn() {
let f = from_fn(|| ~"brail");
assert get(&f) == ~"brail";
}
#[test]
pub fn test_interface_get() {
let f = from_value(~"fail");
assert f.get() == ~"fail";
}
#[test]
pub fn test_with() {
let f = from_value(~"nail");
assert with(&f, |v| copy *v) == ~"nail";
}
#[test]
pub fn test_get_ref_method() {
let f = from_value(22);
assert *f.get_ref() == 22;
}
#[test]
pub fn test_get_ref_fn() {
let f = from_value(22);
assert *get_ref(&f) == 22;
}
#[test]
pub fn test_interface_with() {
let f = from_value(~"kale");
assert f.with(|v| copy *v) == ~"kale";
}
#[test]
pub fn test_spawn() {
let f = spawn(|| ~"bale");
assert get(&f) == ~"bale";
}
#[test]
#[should_fail]
#[ignore(cfg(target_os = "win32"))]
pub fn test_futurefail() {
let f = spawn(|| fail);
let _x: ~str = get(&f);
}
#[test]
pub fn test_sendable_future() {
let expected = ~"schlorf";
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let f = do spawn |copy expected| { copy expected };
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do task::spawn |move f, move expected| {
let actual = get(&f);
assert actual == expected;
}
}
}