pull-spawn
v0.0.7
Published
Spawn pull streams into substreams.
Downloads
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Readme
pull-spawn
Spawn pull streams into substreams.
Usage
spawn(throughCreator, ?onSpawn)
Creates an isolated execution context around the through stream. If the through stream ends with an error, spawn
will
recreate the through stream.
####args
throughCreator
- A callback that should return the through stream.onSpawn
- Optional callback to trigger when spawns.
####example
var pull = require("pull-stream");
var spawn = require("pull-spawn");
pull(
pull.count(20),
spawn( function () {
return function (read) {
return function (end, cb) {
if (Math.round(Math.random() * 3) == 0) { return cb(new Error("random error")); }
read(end, cb);
}
}
}, function() {console.log("spawning")}),
pull.log()
)
spawn.isolate(throughCreator)
Similar to spawn
, but will spawn
a through
on each read. Usefull, when you want to extract one read into multiple
writes.
throughCreator
will get data
as argument. data
is the read result.
example
var pull = require("pull-stream");
var isolate = require("pull-spawn").isolate;
pull(
pull.values([1, 2, 3]),
isolate(function (num) {
console.log("isolating", num);
return pull(
pull.map(function (n) {return n * num})
)
}),
pull.log()
)
spawn.fork(sink)
Forks readable stream into another Sink
other than the main sink.
Respects back-pressure: reads from upstream, only once both sinks are ready to read.
The forked stream will abort if an error ocurred on the main stream. The main stream won't abort if the forked stream was aborted.
args
sink
, as it sounds, should be a sink stream.
pull(
pull.count(10),
spawn.fork(pull.drain(console.error)),
pull.log()
)
You can specify several sinks:
pull(
pull.count(10),
spawn.fork(
sink1,
sink2
),
pull.log()
)
Which is eventually similar to:
pull(
pull.count(10),
spawn.fork(sink1)
spawn.fork(sink2)
pull.log()
)
sink
can also be an array of sinks.
example
var pull = require("pull-stream");
var fork = require("pull-spawn").fork;
var slowMap = pull.asyncMap( function (d, done) {
setTimeout( function () {
done(null, d);
}, 1000)
})
pull(
pull.values([1,2,3,4,5]),
fork(
pull(pull.map(function (d) {return d*10}), pull.log()),
pull(slowMap, pull.map(function () {return "slow fork"}), pull.log())
),
pull.log()
)
advanced usage: fork a through
var read = someSourceStream;
var s = spawn.fork(through)(read);
// main stream
pull(
s,
pull.log();
)
// forked stream
pull(
s.child,
pull.log();
)
As you can see, if you fork a pull-stream manually, you'll be able to access pipedStream.child
and read from it.
spawn.observe(sink)
observe
is exactly the same as fork
, with one difference. It would read as fast as the main sink reads. Which means
that if the observer is a slow sink, it's data will be buffered.
If the observer is faster than the main sink, it will wait the main sink to read.
Everything else, is exactly the same (including the child
property).
example
var pull = require("pull-stream");
var observe = require("pull-spawn").observe;
var slowMap = pull.asyncMap( function (d, done) {
setTimeout( function () {
done(null, d);
}, 1000)
})
pull(
pull.values([1,2,3,4,5]),
observe(
pull(pull.map(function (d) {return d*10}), pull.log()),
pull(slowMap,pull.map(function () {return "observed"}), pull.log())
),
pull.log()
)
spawn.consume(sink)
Similar to observe
and fork
with one main difference. It will pull data from upstream as fast as the fastes consumer
(could be the main consumer, or the alternative consumer). The stream will abort consuming data after the last consumer
was terminated.
install
With npm do:
npm install pull-spawn
license
MIT