flow like the river

BACK_BACK/node_modules/parcel-bundler/lib/utils/PromiseQueue.js

@@ -0,0 +1,109 @@
+"use strict";
+
+var _interopRequireDefault = require("@babel/runtime/helpers/interopRequireDefault");
+
+var _asyncToGenerator2 = _interopRequireDefault(require("@babel/runtime/helpers/asyncToGenerator"));
+
+class PromiseQueue {
+  constructor(callback, options = {}) {
+    this.process = callback;
+    this.maxConcurrent = options.maxConcurrent || Infinity;
+    this.retry = options.retry !== false;
+    this.queue = [];
+    this.processing = new Set();
+    this.processed = new Set();
+    this.numRunning = 0;
+    this.runPromise = null;
+    this.resolve = null;
+    this.reject = null;
+  }
+
+  add(job, ...args) {
+    if (this.processing.has(job)) {
+      return;
+    }
+
+    if (this.runPromise && this.numRunning < this.maxConcurrent) {
+      this._runJob(job, args);
+    } else {
+      this.queue.push([job, args]);
+    }
+
+    this.processing.add(job);
+  }
+
+  run() {
+    if (this.runPromise) {
+      return this.runPromise;
+    }
+
+    const runPromise = new Promise((resolve, reject) => {
+      this.resolve = resolve;
+      this.reject = reject;
+    });
+    this.runPromise = runPromise;
+
+    this._next();
+
+    return runPromise;
+  }
+
+  _runJob(job, args) {
+    var _this = this;
+
+    return (0, _asyncToGenerator2.default)(function* () {
+      try {
+        _this.numRunning++;
+        yield _this.process(job, ...args);
+
+        _this.processing.delete(job);
+
+        _this.processed.add(job);
+
+        _this.numRunning--;
+
+        _this._next();
+      } catch (err) {
+        _this.numRunning--;
+
+        if (_this.retry) {
+          _this.queue.push([job, args]);
+        } else {
+          _this.processing.delete(job);
+        }
+
+        if (_this.reject) {
+          _this.reject(err);
+        }
+
+        _this._reset();
+      }
+    })();
+  }
+
+  _next() {
+    if (!this.runPromise) {
+      return;
+    }
+
+    if (this.queue.length > 0) {
+      while (this.queue.length > 0 && this.numRunning < this.maxConcurrent) {
+        this._runJob(...this.queue.shift());
+      }
+    } else if (this.processing.size === 0) {
+      this.resolve(this.processed);
+
+      this._reset();
+    }
+  }
+
+  _reset() {
+    this.processed = new Set();
+    this.runPromise = null;
+    this.resolve = null;
+    this.reject = null;
+  }
+
+}
+
+module.exports = PromiseQueue;