allow concurrent removals when iterating pending events

so we can remove failed events in the next commit

src/matrix/room/sending/SendQueue.js

@@ -47,25 +47,11 @@ export class SendQueue {
         this._roomEncryption = roomEncryption;
     }
 
-    _nextPendingEvent(current) {
-        if (!current) {
-            return this._pendingEvents.get(0);
-        } else {
-            const idx = this._pendingEvents.indexOf(current);
-            if (idx !== -1) {
-                return this._pendingEvents.get(idx + 1);
-            }
-            return;
-        }
-    }
-
     _sendLoop(log) {
         this._isSending = true;
         this._sendLoopLogItem = log.runDetached("send queue flush", async log => {
-            let pendingEvent;
             try {
-                // eslint-disable-next-line no-cond-assign
-                while (pendingEvent = this._nextPendingEvent(pendingEvent)) {
+                for (const pendingEvent of this._pendingEvents) {
                     await log.wrap("send event", async log => {
                         log.set("queueIndex", pendingEvent.queueIndex);
                         try {

src/observable/list/SortedArray.js

@@ -58,6 +58,14 @@ export class SortedArray extends BaseObservableList {
         }
     }
 
+    _getNext(item) {
+        let idx = sortedIndex(this._items, item, this._comparator);
+        while(idx < this._items.length && this._comparator(this._items[idx], item) <= 0) {
+            idx += 1;
+        }
+        return this.get(idx);
+    }
+
     set(item, updateParams = null) {
         const idx = sortedIndex(this._items, item, this._comparator);
         if (idx >= this._items.length || this._comparator(this._items[idx], item) !== 0) {
@@ -88,6 +96,72 @@ export class SortedArray extends BaseObservableList {
     }
 
     [Symbol.iterator]() {
-        return this._items.values();
+        return new Iterator(this);
     }
 }
+
+// iterator that works even if the current value is removed while iterating
+class Iterator {
+    constructor(sortedArray) {
+        this._sortedArray = sortedArray;
+        this._current = null;
+    }
+
+    next() {
+        if (this._sortedArray) {
+            if (this._current) {
+                this._current = this._sortedArray._getNext(this._current);
+            } else {
+                this._current = this._sortedArray.get(0);
+            }
+            if (this._current) {
+                return {value: this._current};
+            } else {
+                // cause done below
+                this._sortedArray = null;
+            }
+        }
+        if (!this._sortedArray) {
+            return {done: true};
+        }
+    }
+}
+
+export function tests() {
+    return {
+        "setManyUnsorted": assert => {
+            const sa = new SortedArray((a, b) => a.localeCompare(b));
+            sa.setManyUnsorted(["b", "a", "c"]);
+            assert.equal(sa.length, 3);
+            assert.equal(sa.get(0), "a");
+            assert.equal(sa.get(1), "b");
+            assert.equal(sa.get(2), "c");
+        }, 
+        "_getNext": assert => {
+            const sa = new SortedArray((a, b) => a.localeCompare(b));
+            sa.setManyUnsorted(["b", "a", "f"]);
+            assert.equal(sa._getNext("a"), "b");
+            assert.equal(sa._getNext("b"), "f");
+            // also finds the next if the value is not in the collection
+            assert.equal(sa._getNext("c"), "f");
+            assert.equal(sa._getNext("f"), undefined);
+        },
+        "iterator with removals": assert => {
+            const queue = new SortedArray((a, b) => a.idx - b.idx);
+            queue.setManyUnsorted([{idx: 5}, {idx: 3}, {idx: 1}, {idx: 4}, {idx: 2}]);
+            const it = queue[Symbol.iterator]();
+            assert.equal(it.next().value.idx, 1);
+            assert.equal(it.next().value.idx, 2);
+            queue.remove(1);
+            assert.equal(it.next().value.idx, 3);
+            queue.remove(1);
+            assert.equal(it.next().value.idx, 4);
+            queue.remove(1);
+            assert.equal(it.next().value.idx, 5);
+            queue.remove(1);
+            assert.equal(it.next().done, true);
+            // check done persists
+            assert.equal(it.next().done, true);
+        }
+    }
+}