public static Future any(IEnumerable <Future> futures)
{
var completer = Completer.sync();
Func <object, FutureOr> onValue = (object value) => {
if (!completer.isCompleted)
{
completer.complete(FutureOr.value(value));
}
return(FutureOr.nil);
};
Func <Exception, FutureOr> onError = (Exception error) => {
if (!completer.isCompleted)
{
completer.completeError(error);
}
return(FutureOr.nil);
};
foreach (var future in futures)
{
future.then(onValue, onError: onError);
}
return(completer.future);
}
internal void _asyncComplete(FutureOr value)
{
D.assert(!_isComplete);
// Two corner cases if the value is a future:
// 1. the future is already completed and an error.
// 2. the future is not yet completed but might become an error.
// The first case means that we must not immediately complete the Future,
// as our code would immediately start propagating the error without
// giving the time to install error-handlers.
// However the second case requires us to deal with the value immediately.
// Otherwise the value could complete with an error and report an
// unhandled error, even though we know we are already going to listen to
// it.
if (value.isFuture)
{
_chainFuture(value.f);
return;
}
_setPendingComplete();
_zone.scheduleMicrotask(() => {
_completeWithValue(value.v);
return(null);
});
}
static void _chainForeignFuture(Future source, _Future target)
{
D.assert(!target._isComplete);
D.assert(!(source is _Future));
// Mark the target as chained (and as such half-completed).
target._setPendingComplete();
try {
source.then((value) => {
D.assert(target._isPendingComplete);
// The "value" may be another future if the foreign future
// implementation is mis-behaving,
// so use _complete instead of _completeWithValue.
target._clearPendingComplete(); // Clear this first, it's set again.
target._complete(FutureOr.value(value));
return(new FutureOr());
},
onError: (Exception error) => {
D.assert(target._isPendingComplete);
target._completeError(error);
return(new FutureOr());
});
}
catch (Exception e) {
// This only happens if the `then` call threw synchronously when given
// valid arguments.
// That requires a non-conforming implementation of the Future interface,
// which should, hopefully, never happen.
async_.scheduleMicrotask(() => {
target._completeError(e);
return(null);
});
}
}
internal static _Future immediate(FutureOr result)
{
var future = new _Future(Zone.current);
future._asyncComplete(result);
return(future);
}
public override void complete(FutureOr value = default)
{
if (!_future._mayComplete)
{
throw new Exception("Future already completed");
}
_future._complete(value);
}
internal static void _cancelAndValue <T>(StreamSubscription <T> subscription, _Future future, object value)
{
var cancelFuture = subscription.cancel();
if (cancelFuture != null && !Equals(cancelFuture, Future._nullFuture))
{
cancelFuture.whenComplete(() => future._complete(FutureOr.value(value)));
}
else
{
future._complete(FutureOr.value(value));
}
}
Future <S> fold <S>(S initialValue, Func <S, T, S> combine)
{
_Future result = new _Future();
S value = initialValue;
StreamSubscription <T> subscription = null;
subscription = listen(
(T element) => {
_stream._runUserCode(() => combine(value, element), (S newValue) => { value = newValue; },
e => _stream._cancelAndErrorClosure(subscription, result)(e));
},
onError: (e, s) => result._completeError((Exception)e),
onDone: () => { result._complete(FutureOr.value(value)); },
cancelOnError: true);
return(result.to <S>());
}
public static Future forEach <T>(IEnumerable <T> elements, Func <T, FutureOr> action)
{
var iterator = elements.GetEnumerator();
return(doWhile(() => {
if (!iterator.MoveNext())
{
return false;
}
var result = action(iterator.Current);
if (result.isFuture)
{
return FutureOr.future(result.f.then(_kTrue));
}
return true;
}));
}
Future <T> reduce(Func <T, T, T> combine)
{
_Future result = new _Future();
bool seenFirst = false;
T value = default;
StreamSubscription <T> subscription = null;
subscription = listen(
(T element) => {
if (seenFirst)
{
_stream._runUserCode(() => combine(value, element), (T newValue) => { value = newValue; },
onError: (e) => _stream._cancelAndErrorClosure(subscription, result)(e));
}
else
{
value = element;
seenFirst = true;
}
},
onError: (e, s) => result._completeError((Exception)e),
onDone: () => {
if (!seenFirst)
{
try {
// Throw and recatch, instead of just doing
// _completeWithErrorCallback, e, theError, StackTrace.current),
// to ensure that the stackTrace is set on the error.
throw new Exception("IterableElementError.noElement()");
}
catch (Exception e) {
async_._completeWithErrorCallback(result, e);
}
}
else
{
// TODO: need check
result._complete(FutureOr.value(value));
}
},
cancelOnError: true);
return(result.to <T>());
}
internal void _complete(FutureOr value = default)
{
D.assert(!_isComplete);
if (value.isFuture)
{
if (value.f is _Future coreFuture)
{
_chainCoreFuture(coreFuture, this);
}
else
{
_chainForeignFuture(value.f, this);
}
}
else
{
_FutureListener listeners = _removeListeners();
_setValue(value.v);
_propagateToListeners(this, listeners);
}
}
public abstract void complete(FutureOr value = default);
public static Future wait <T>(IEnumerable <Future> futures, bool eagerError = false, Action <T> cleanUp = null)
{
_Future result = new _Future();
List <T> values = null; // Collects the values. Set to null on error.
int remaining = 0; // How many futures are we waiting for.
Exception error = null; // The first error from a future.
Func <Exception, FutureOr> handleError = (Exception theError) => {
remaining--;
if (values != null)
{
if (cleanUp != null)
{
foreach (var value in values)
{
if (value != null)
{
// Ensure errors from cleanUp are uncaught.
sync(() => {
cleanUp(value);
return(FutureOr.nil);
});
}
}
}
values = null;
if (remaining == 0 || eagerError)
{
result._completeError(theError);
}
else
{
error = theError;
}
}
else if (remaining == 0 && !eagerError)
{
result._completeError(error);
}
return(FutureOr.nil);
};
try {
// As each future completes, put its value into the corresponding
// position in the list of values.
foreach (var future in futures)
{
int pos = remaining;
future.then((object value) => {
remaining--;
if (values != null)
{
values[pos] = (T)value;
if (remaining == 0)
{
result._completeWithValue(values);
}
}
else
{
if (cleanUp != null && value != null)
{
// Ensure errors from cleanUp are uncaught.
sync(() => {
cleanUp((T)value);
return(FutureOr.nil);
});
}
if (remaining == 0 && !eagerError)
{
result._completeError(error);
}
}
return(FutureOr.nil);
}, onError: handleError);
// Increment the 'remaining' after the call to 'then'.
// If that call throws, we don't expect any future callback from
// the future, and we also don't increment remaining.
remaining++;
}
if (remaining == 0)
{
return(value(FutureOr.value(new List <T>())));
}
values = new List <T>(new T[remaining]);
}
catch (Exception e) {
// The error must have been thrown while iterating over the futures
// list, or while installing a callback handler on the future.
if (remaining == 0 || eagerError)
{
// Throw a new Future.error.
// Don't just call `result._completeError` since that would propagate
// the error too eagerly, not giving the callers time to install
// error handlers.
// Also, don't use `_asyncCompleteError` since that one doesn't give
// zones the chance to intercept the error.
return(Future.error(e));
}
else
{
// Don't allocate a list for values, thus indicating that there was an
// error.
// Set error to the caught exception.
error = e;
}
}
return(result);
}
public static Future value(FutureOr value = default)
{
return(_Future.immediate(value));
}
static void _propagateToListeners(_Future source, _FutureListener listeners)
{
while (true)
{
D.assert(source._isComplete);
bool hasError = source._hasError;
if (listeners == null)
{
if (hasError)
{
AsyncError asyncError = source._error;
source._zone.handleUncaughtError(asyncError);
}
return;
}
// Usually futures only have one listener. If they have several, we
// call handle them separately in recursive calls, continuing
// here only when there is only one listener left.
while (listeners._nextListener != null)
{
_FutureListener currentListener = listeners;
listeners = currentListener._nextListener;
currentListener._nextListener = null;
_propagateToListeners(source, currentListener);
}
_FutureListener listener = listeners;
var sourceResult = source._resultOrListeners;
// Do the actual propagation.
// Set initial state of listenerHasError and listenerValueOrError. These
// variables are updated with the outcome of potential callbacks.
// Non-error results, including futures, are stored in
// listenerValueOrError and listenerHasError is set to false. Errors
// are stored in listenerValueOrError as an [AsyncError] and
// listenerHasError is set to true.
bool listenerHasError = hasError;
var listenerValueOrError = sourceResult;
// Only if we either have an error or callbacks, go into this, somewhat
// expensive, branch. Here we'll enter/leave the zone. Many futures
// don't have callbacks, so this is a significant optimization.
if (hasError || listener.handlesValue || listener.handlesComplete)
{
Zone zone = listener._zone;
if (hasError && !source._zone.inSameErrorZone(zone))
{
// Don't cross zone boundaries with errors.
AsyncError asyncError = source._error;
source._zone.handleUncaughtError(asyncError);
return;
}
Zone oldZone = null;
if (!ReferenceEquals(Zone.current, zone))
{
// Change zone if it's not current.
oldZone = Zone._enter(zone);
}
// These callbacks are abstracted to isolate the try/catch blocks
// from the rest of the code to work around a V8 glass jaw.
Action handleWhenCompleteCallback = () => {
// The whenComplete-handler is not combined with normal value/error
// handling. This means at most one handleX method is called per
// listener.
D.assert(!listener.handlesValue);
D.assert(!listener.handlesError);
FutureOr completeResult;
try {
completeResult = listener.handleWhenComplete();
}
catch (Exception e) {
if (hasError && ReferenceEquals(source._error.InnerException, e))
{
listenerValueOrError = source._error;
}
else
{
listenerValueOrError = new AsyncError(e);
}
listenerHasError = true;
return;
}
if (completeResult.isFuture)
{
var completeResultFuture = completeResult.f;
if (completeResultFuture is _Future completeResultCoreFuture &&
completeResultCoreFuture._isComplete)
{
if (completeResultCoreFuture._hasError)
{
listenerValueOrError = completeResultCoreFuture._error;
listenerHasError = true;
}
// Otherwise use the existing result of source.
return;
}
// We have to wait for the completeResult future to complete
// before knowing if it's an error or we should use the result
// of source.
var originalSource = source;
listenerValueOrError =
completeResultFuture.then((_) => FutureOr.future(originalSource));
listenerHasError = false;
}
};
Action handleValueCallback = () => {
try {
listenerValueOrError = listener.handleValue(sourceResult);
}
catch (Exception e) {
listenerValueOrError = new AsyncError(e);
listenerHasError = true;
}
};
Action handleError = () => {
try {
AsyncError asyncError = source._error;
if (listener.matchesErrorTest(asyncError) &&
listener.hasErrorCallback)
{
listenerValueOrError = listener.handleError(asyncError);
listenerHasError = false;
}
}
catch (Exception e) {
if (ReferenceEquals(source._error.InnerException, e))
{
listenerValueOrError = source._error;
}
else
{
listenerValueOrError = new AsyncError(e);
}
listenerHasError = true;
}
};
if (listener.handlesComplete)
{
handleWhenCompleteCallback();
}
else if (!hasError)
{
if (listener.handlesValue)
{
handleValueCallback();
}
}
else
{
if (listener.handlesError)
{
handleError();
}
}
// If we changed zone, oldZone will not be null.
if (oldZone != null)
{
Zone._leave(oldZone);
}
if (listenerValueOrError is FutureOr futureOr)
{
listenerValueOrError = futureOr.isFuture ? futureOr.f : futureOr.v;
}
// If the listener's value is a future we need to chain it. Note that
// this can only happen if there is a callback.
if (listenerValueOrError is Future chainSource)
{
// Shortcut if the chain-source is already completed. Just continue
// the loop.
_Future listenerResult = listener.result;
if (chainSource is _Future chainSourceCore)
{
if (chainSourceCore._isComplete)
{
listeners = listenerResult._removeListeners();
listenerResult._cloneResult(chainSourceCore);
source = chainSourceCore;
continue;
}
else
{
_chainCoreFuture(chainSourceCore, listenerResult);
}
}
else
{
_chainForeignFuture(chainSource, listenerResult);
}
return;
}
}
_Future result = listener.result;
listeners = result._removeListeners();
if (!listenerHasError)
{
result._setValue(listenerValueOrError);
}
else
{
AsyncError asyncError = (AsyncError)listenerValueOrError;
result._setErrorObject(asyncError);
}
// Prepare for next round.
source = result;
}
}