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import indexOf from 'lodash/_baseIndexOf';
import isArray from 'lodash/isArray';
import noop from 'lodash/noop';
import rest from './rest';
import onlyOnce from './onlyOnce';
import setImmediate from './setImmediate';
import DLL from './DoublyLinkedList';
import wrapAsync from './wrapAsync';
export default function queue(worker, concurrency, payload) {
if (concurrency == null) {
concurrency = 1;
}
else if(concurrency === 0) {
throw new Error('Concurrency must not be zero');
}
var _worker = wrapAsync(worker);
var numRunning = 0;
var workersList = [];
function _insert(data, insertAtFront, 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();
});
}
for (var i = 0, l = data.length; i < l; i++) {
var item = {
data: data[i],
callback: callback || noop
};
if (insertAtFront) {
q._tasks.unshift(item);
} else {
q._tasks.push(item);
}
}
setImmediate(q.process);
}
function _next(tasks) {
return rest(function(args){
numRunning -= 1;
for (var i = 0, l = tasks.length; i < l; i++) {
var task = tasks[i];
var index = indexOf(workersList, task, 0);
if (index >= 0) {
workersList.splice(index)
}
task.callback.apply(task, args);
if (args[0] != null) {
q.error(args[0], task.data);
}
}
if (numRunning <= (q.concurrency - q.buffer) ) {
q.unsaturated();
}
if (q.idle()) {
q.drain();
}
q.process();
});
}
var isProcessing = false;
var q = {
_tasks: new DLL(),
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(data, false, callback);
},
kill: function () {
q.drain = noop;
q._tasks.empty();
},
unshift: function (data, callback) {
_insert(data, true, callback);
},
remove: function (testFn) {
q._tasks = q._tasks.filter(function (node) {
return !testFn(node);
})
},
process: function () {
// Avoid trying to start too many processing operations. This can occur
// when callbacks resolve synchronously (#1267).
if (isProcessing) {
return;
}
isProcessing = true;
while(!q.paused && numRunning < q.concurrency && q._tasks.length){
var tasks = [], data = [];
var l = q._tasks.length;
if (q.payload) l = Math.min(l, q.payload);
for (var i = 0; i < l; i++) {
var node = q._tasks.shift();
tasks.push(node);
data.push(node.data);
}
numRunning += 1;
workersList.push(tasks[0]);
if (q._tasks.length === 0) {
q.empty();
}
if (numRunning === q.concurrency) {
q.saturated();
}
var cb = onlyOnce(_next(tasks));
_worker(data, cb);
}
isProcessing = false;
},
length: function () {
return q._tasks.length;
},
running: function () {
return numRunning;
},
workersList: function () {
return workersList;
},
idle: function() {
return q._tasks.length + numRunning === 0;
},
pause: function () {
q.paused = true;
},
resume: function () {
if (q.paused === false) { return; }
q.paused = false;
setImmediate(q.process);
}
};
return q;
}
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