some progress

node_modules/mongoose/lib/helpers/cursor/eachAsync.js

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+'use strict';
+
+/*!
+ * Module dependencies.
+ */
+
+const EachAsyncMultiError = require('../../error/eachAsyncMultiError');
+const immediate = require('../immediate');
+
+/**
+ * Execute `fn` for every document in the cursor. If `fn` returns a promise,
+ * will wait for the promise to resolve before iterating on to the next one.
+ * Returns a promise that resolves when done.
+ *
+ * @param {Function} next the thunk to call to get the next document
+ * @param {Function} fn
+ * @param {Object} options
+ * @param {Number} [options.batchSize=null] if set, Mongoose will call `fn` with an array of at most `batchSize` documents, instead of a single document
+ * @param {Number} [options.parallel=1] maximum number of `fn` calls that Mongoose will run in parallel
+ * @param {AbortSignal} [options.signal] allow cancelling this eachAsync(). Once the abort signal is fired, `eachAsync()` will immediately fulfill the returned promise (or call the callback) and not fetch any more documents.
+ * @return {Promise}
+ * @api public
+ * @method eachAsync
+ */
+
+module.exports = async function eachAsync(next, fn, options) {
+  const parallel = options.parallel || 1;
+  const batchSize = options.batchSize;
+  const signal = options.signal;
+  const continueOnError = options.continueOnError;
+  const aggregatedErrors = [];
+  const enqueue = asyncQueue();
+
+  let aborted = false;
+
+  return new Promise((resolve, reject) => {
+    if (signal != null) {
+      if (signal.aborted) {
+        return resolve(null);
+      }
+
+      signal.addEventListener('abort', () => {
+        aborted = true;
+        return resolve(null);
+      }, { once: true });
+    }
+
+    if (batchSize != null) {
+      if (typeof batchSize !== 'number') {
+        throw new TypeError('batchSize must be a number');
+      } else if (!Number.isInteger(batchSize)) {
+        throw new TypeError('batchSize must be an integer');
+      } else if (batchSize < 1) {
+        throw new TypeError('batchSize must be at least 1');
+      }
+    }
+
+    iterate((err, res) => {
+      if (err != null) {
+        return reject(err);
+      }
+      resolve(res);
+    });
+  });
+
+  function iterate(finalCallback) {
+    let handleResultsInProgress = 0;
+    let currentDocumentIndex = 0;
+
+    let error = null;
+    for (let i = 0; i < parallel; ++i) {
+      enqueue(createFetch());
+    }
+
+    function createFetch() {
+      let documentsBatch = [];
+      let drained = false;
+
+      return fetch;
+
+      function fetch(done) {
+        if (drained || aborted) {
+          return done();
+        } else if (error) {
+          return done();
+        }
+
+        next(function(err, doc) {
+          if (error != null) {
+            return done();
+          }
+          if (err != null) {
+            if (err.name === 'MongoCursorExhaustedError') {
+              // We may end up calling `next()` multiple times on an exhausted
+              // cursor, which leads to an error. In case cursor is exhausted,
+              // just treat it as if the cursor returned no document, which is
+              // how a cursor indicates it is exhausted.
+              doc = null;
+            } else if (continueOnError) {
+              aggregatedErrors.push(err);
+            } else {
+              error = err;
+              finalCallback(err);
+              return done();
+            }
+          }
+          if (doc == null) {
+            drained = true;
+            if (handleResultsInProgress <= 0) {
+              const finalErr = continueOnError ?
+                createEachAsyncMultiError(aggregatedErrors) :
+                error;
+
+              finalCallback(finalErr);
+            } else if (batchSize && documentsBatch.length) {
+              handleNextResult(documentsBatch, currentDocumentIndex++, handleNextResultCallBack);
+            }
+            return done();
+          }
+
+          ++handleResultsInProgress;
+
+          // Kick off the subsequent `next()` before handling the result, but
+          // make sure we know that we still have a result to handle re: #8422
+          immediate(() => done());
+
+          if (batchSize) {
+            documentsBatch.push(doc);
+          }
+
+          // If the current documents size is less than the provided batch size don't process the documents yet
+          if (batchSize && documentsBatch.length !== batchSize) {
+            immediate(() => enqueue(fetch));
+            return;
+          }
+
+          const docsToProcess = batchSize ? documentsBatch : doc;
+
+          function handleNextResultCallBack(err) {
+            if (batchSize) {
+              handleResultsInProgress -= documentsBatch.length;
+              documentsBatch = [];
+            } else {
+              --handleResultsInProgress;
+            }
+            if (err != null) {
+              if (continueOnError) {
+                aggregatedErrors.push(err);
+              } else {
+                error = err;
+                return finalCallback(err);
+              }
+            }
+            if ((drained || aborted) && handleResultsInProgress <= 0) {
+              const finalErr = continueOnError ?
+                createEachAsyncMultiError(aggregatedErrors) :
+                error;
+              return finalCallback(finalErr);
+            }
+
+            immediate(() => enqueue(fetch));
+          }
+
+          handleNextResult(docsToProcess, currentDocumentIndex++, handleNextResultCallBack);
+        });
+      }
+    }
+  }
+
+  function handleNextResult(doc, i, callback) {
+    let maybePromise;
+    try {
+      maybePromise = fn(doc, i);
+    } catch (err) {
+      return callback(err);
+    }
+    if (maybePromise && typeof maybePromise.then === 'function') {
+      maybePromise.then(
+        function() { callback(null); },
+        function(error) {
+          callback(error || new Error('`eachAsync()` promise rejected without error'));
+        });
+    } else {
+      callback(null);
+    }
+  }
+};
+
+// `next()` can only execute one at a time, so make sure we always execute
+// `next()` in series, while still allowing multiple `fn()` instances to run
+// in parallel.
+function asyncQueue() {
+  const _queue = [];
+  let inProgress = null;
+  let id = 0;
+
+  return function enqueue(fn) {
+    if (
+      inProgress === null &&
+      _queue.length === 0
+    ) {
+      inProgress = id++;
+      return fn(_step);
+    }
+    _queue.push(fn);
+  };
+
+  function _step() {
+    if (_queue.length !== 0) {
+      inProgress = id++;
+      const fn = _queue.shift();
+      fn(_step);
+    } else {
+      inProgress = null;
+    }
+  }
+}
+
+function createEachAsyncMultiError(aggregatedErrors) {
+  if (aggregatedErrors.length === 0) {
+    return null;
+  }
+
+  return new EachAsyncMultiError(aggregatedErrors);
+}