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/* lazy.vala
*
* Copyright (C) 2011 Maciej Piechotka
*
* This library 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; either
* version 2.1 of the License, or (at your option) any later version.
* This library 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.
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Author:
* Maciej Piechotka <uzytkownik2@gmail.com>
*/
namespace Gee {
public delegate G LazyFunc<G> ();
}
/**
* Represents a lazy value. I.e. value that is computed on demand.
*
* This class is not thread-safe.
*/
public class Gee.Lazy<G> {
public Lazy (owned LazyFunc<G> func) {
_func = (owned)func;
}
public Lazy.from_value (G item) {
_value = item;
}
public void eval () {
if (_func != null) {
_value = _func ();
_func = null;
}
}
public new G get () {
eval ();
return _value;
}
public new G value {
get {
eval ();
return _value;
}
}
/**
* Provides a future for a lazy value.
*
* Note: The future can be requested only once and all access must be
* done through it.
*/
public Gee.Future<G>? future {
owned get {
return new Future<G> (this);
}
}
private LazyFunc<G>? _func;
private G? _value;
private class Future<G> : Object, Gee.Future<G> {
public Future (Lazy<G> lazy) {
_lazy = lazy;
_when_done = new Gee.Future.SourceFuncArrayElement<G>[0];
}
public bool ready {
get {
_mutex.lock ();
bool result = _lazy._func == null;
_mutex.unlock ();
return result;
}
}
public GLib.Error? exception {get {return null;}}
public unowned G wait () throws Gee.FutureError {
_mutex.lock ();
if (_lazy._func != null) {
if (_state == State.EVAL) {
_eval.wait (_mutex);
_mutex.unlock ();
} else {
do_eval ();
}
} else {
_mutex.unlock ();
}
return _lazy._value;
}
public unowned bool wait_until (int64 end_time, out unowned G? value = null) throws Gee.FutureError {
_mutex.lock ();
if (_lazy._func != null) {
if (_state == State.EVAL) {
bool res = _eval.wait_until (_mutex, end_time);
_mutex.unlock ();
if (!res) {
value = null;
return false;
}
} else {
do_eval ();
}
} else {
_mutex.unlock ();
}
value = _lazy._value;
return true;
}
public async unowned G wait_async () throws Gee.FutureError {
_mutex.lock ();
if (_lazy._func != null) {
if (_state == State.EVAL) {
_when_done += SourceFuncArrayElement(wait_async.callback);
yield Gee.Utils.Async.yield_and_unlock (_mutex);
} else {
do_eval ();
}
} else {
_mutex.unlock ();
}
return _lazy.value;
}
private void do_eval () {
_state = State.EVAL;
_mutex.unlock ();
_lazy._value = _lazy._func ();
_mutex.lock ();
_lazy._func = null;
_state = State.UNLOCK;
_eval.broadcast ();
_mutex.unlock ();
Gee.Future.SourceFuncArrayElement<G>[] when_done = (owned)_when_done;
for (int i = 0; i < when_done.length; i++) {
when_done[i].func ();
}
}
private Mutex _mutex = Mutex ();
private Cond _eval = Cond ();
private Lazy<G> _lazy;
private State _state = State.UNLOCK;
private Gee.Future.SourceFuncArrayElement<G>[]? _when_done;
private enum State {
UNLOCK,
EVAL
}
}
}
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