StreamQueue< T> class
An asynchronous pull-based interface for accessing stream events.
Wraps a stream and makes individual events available on request.
You can request (and reserve) one or more events from the stream, and after all previous requests have been fulfilled, stream events go towards fulfilling your request.
For example, if you ask for next two times, the returned futures will be completed by the next two unrequested events from the stream.
The stream subscription is paused when there are no active requests.
Some streams, including broadcast streams, will buffer events while paused, so waiting too long between requests may cause memory bloat somewhere else.
This is similar to, but more convenient than, a StreamIterator.
A StreamIterator
requires you to manually check when a new event is
available and you can only access the value of that event until you
check for the next one. A StreamQueue
allows you to request, for example,
three events at a time, either individually, as a group using take
or skip, or in any combination.
You can also ask to have the rest of the stream provided as a new stream. This allows, for example, taking the first event out of a stream and continuing to use the rest of the stream as a stream.
Example:
var events = new StreamQueue<String>(someStreamOfLines);
var first = await events.next;
while (first.startsWith('#')) {
// Skip comments.
first = await events.next;
}
if (first.startsWith(MAGIC_MARKER)) {
var headerCount =
first.parseInt(first.substring(MAGIC_MARKER.length + 1));
handleMessage(headers: await events.take(headerCount),
body: events.rest);
return;
}
// Error handling.
When you need no further events the StreamQueue
should be closed
using cancel. This releases the underlying stream subscription.
Constructors
-
StreamQueue(Stream<
T> source) -
Create a
StreamQueue
of the events ofsource
.factory
Properties
- eventsDispatched → int
-
The number of events dispatched by this queue. [...]
read-only
-
hasNext
→ Future<
bool> -
Asks if the stream has any more events. [...]
read-only
-
next
→ Future<
T> -
Requests the next (yet unrequested) event from the stream. [...]
read-only
-
peek
→ Future<
T> -
Looks at the next (yet unrequested) event from the stream. [...]
read-only
-
rest
→ Stream<
T> -
Returns a stream of all the remaning events of the source stream. [...]
read-only
- hashCode → int
-
The hash code for this object. [...]
read-only, inherited
- runtimeType → Type
-
A representation of the runtime type of the object.
read-only, inherited
Methods
-
cancel(
{bool immediate: false }) → Future - Cancels the underlying event source. [...]
-
cancelable<
S>( Future< S> callback(StreamQueue< T> queue)) → CancelableOperation< S> -
Passes a copy of this queue to
callback
, and updates this queue to match the copy's position oncecallback
completes. [...] -
lookAhead(
int count) → Future< List< T>> -
Look at the next
count
data events without consuming them. [...] -
skip(
int count) → Future< int> -
Skips the next
count
data events. [...] -
startTransaction(
) → StreamQueueTransaction< T> - Requests a transaction that can conditionally consume events. [...]
-
take(
int count) → Future< List< T>> -
Requests the next
count
data events as a list. [...] -
withTransaction(
Future< bool> callback(StreamQueue< T> queue)) → Future< bool> -
Passes a copy of this queue to
callback
, and updates this queue to match the copy's position ifcallback
returnstrue
. [...] -
noSuchMethod(
Invocation invocation) → dynamic -
Invoked when a non-existent method or property is accessed. [...]
inherited
-
toString(
) → String -
Returns a string representation of this object.
inherited
Operators
-
operator ==(
dynamic other) → bool -
The equality operator. [...]
inherited