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import arrayEach from 'lodash/_arrayEach';
import arrayMap from 'lodash/_arrayMap';
import isArray from 'lodash/isArray';
import noop from 'lodash/noop';
import property from 'lodash/_baseProperty';
import onlyOnce from './onlyOnce';
import setImmediate from './setImmediate';
export default function queue(worker, concurrency, payload) {
if (concurrency == null) {
concurrency = 1;
}
else if(concurrency === 0) {
throw new Error('Concurrency must not be zero');
}
function _insert(q, data, pos, callback) {
if (callback != null && typeof callback !== 'function') {
throw new Error('task callback must be a function');
}
q.started = true;
if (!isArray(data)) {
data = [data];
}
if(data.length === 0 && q.idle()) {
// call drain immediately if there are no tasks
return setImmediate(function() {
q.drain();
});
}
arrayEach(data, function(task) {
var item = {
data: task,
callback: callback || noop
};
if (pos) {
q.tasks.unshift(item);
} else {
q.tasks.push(item);
}
});
setImmediate(q.process);
}
function _next(q, tasks) {
return function(){
workers -= 1;
var removed = false;
var args = arguments;
arrayEach(tasks, function (task) {
arrayEach(workersList, function (worker, index) {
if (worker === task && !removed) {
workersList.splice(index, 1);
removed = true;
}
});
task.callback.apply(task, args);
if (args[0] != null) {
q.error(args[0], task.data);
}
});
if (workers <= (q.concurrency - q.buffer) ) {
q.unsaturated();
}
if (q.tasks.length + workers === 0) {
q.drain();
}
q.process();
};
}
var workers = 0;
var workersList = [];
var q = {
tasks: [],
concurrency: concurrency,
payload: payload,
saturated: noop,
unsaturated:noop,
buffer: concurrency / 4,
empty: noop,
drain: noop,
error: noop,
started: false,
paused: false,
push: function (data, callback) {
_insert(q, data, false, callback);
},
kill: function () {
q.drain = noop;
q.tasks = [];
},
unshift: function (data, callback) {
_insert(q, data, true, callback);
},
process: function () {
while(!q.paused && workers < q.concurrency && q.tasks.length){
var tasks = q.payload ?
q.tasks.splice(0, q.payload) :
q.tasks.splice(0, q.tasks.length);
var data = arrayMap(tasks, property('data'));
if (q.tasks.length === 0) {
q.empty();
}
workers += 1;
workersList.push(tasks[0]);
if (workers === q.concurrency) {
q.saturated();
}
var cb = onlyOnce(_next(q, tasks));
worker(data, cb);
}
},
length: function () {
return q.tasks.length;
},
running: function () {
return workers;
},
workersList: function () {
return workersList;
},
idle: function() {
return q.tasks.length + workers === 0;
},
pause: function () {
q.paused = true;
},
resume: function () {
if (q.paused === false) { return; }
q.paused = false;
var resumeCount = Math.min(q.concurrency, q.tasks.length);
// Need to call q.process once per concurrent
// worker to preserve full concurrency after pause
for (var w = 1; w <= resumeCount; w++) {
setImmediate(q.process);
}
}
};
return q;
}
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