Only fetching TaskManager's available tasks once per call to fillPool (#61991)

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

Author: kobelb

x-pack/plugins/task_manager/server/lib/fill_pool.test.ts

@@ -10,7 +10,7 @@ import { fillPool } from './fill_pool';
 import { TaskPoolRunResult } from '../task_pool';
 
 describe('fillPool', () => {
-  test('stops filling when there are no more tasks in the store', async () => {
+  test('stops filling when pool runs all claimed tasks, even if there is more capacity', async () => {
     const tasks = [
       [1, 2, 3],
       [4, 5],
@@ -22,7 +22,7 @@ describe('fillPool', () => {
 
     await fillPool(fetchAvailableTasks, converter, run);
 
-    expect(_.flattenDeep(run.args)).toEqual([1, 2, 3, 4, 5]);
+    expect(_.flattenDeep(run.args)).toEqual([1, 2, 3]);
   });
 
   test('stops filling when the pool has no more capacity', async () => {

x-pack/plugins/task_manager/server/lib/fill_pool.ts

@@ -5,12 +5,12 @@
  */
 
 import { performance } from 'perf_hooks';
-import { after } from 'lodash';
 import { TaskPoolRunResult } from '../task_pool';
 
 export enum FillPoolResult {
   NoTasksClaimed = 'NoTasksClaimed',
   RanOutOfCapacity = 'RanOutOfCapacity',
+  PoolFilled = 'PoolFilled',
 }
 
 type BatchRun<T> = (tasks: T[]) => Promise<TaskPoolRunResult>;
@@ -35,33 +35,28 @@ export async function fillPool<TRecord, TRunner>(
   run: BatchRun<TRunner>
 ): Promise<FillPoolResult> {
   performance.mark('fillPool.start');
-  const markClaimedTasksOnRerunCycle = after(2, () =>
-    performance.mark('fillPool.claimedOnRerunCycle')
-  );
-  while (true) {
-    const instances = await fetchAvailableTasks();
+  const instances = await fetchAvailableTasks();
 
-    if (!instances.length) {
-      performance.mark('fillPool.bailNoTasks');
-      performance.measure(
-        'fillPool.activityDurationUntilNoTasks',
-        'fillPool.start',
-        'fillPool.bailNoTasks'
-      );
-      return FillPoolResult.NoTasksClaimed;
-    }
-    markClaimedTasksOnRerunCycle();
-    const tasks = instances.map(converter);
+  if (!instances.length) {
+    performance.mark('fillPool.bailNoTasks');
+    performance.measure(
+      'fillPool.activityDurationUntilNoTasks',
+      'fillPool.start',
+      'fillPool.bailNoTasks'
+    );
+    return FillPoolResult.NoTasksClaimed;
+  }
+  const tasks = instances.map(converter);
 
-    if ((await run(tasks)) === TaskPoolRunResult.RanOutOfCapacity) {
-      performance.mark('fillPool.bailExhaustedCapacity');
-      performance.measure(
-        'fillPool.activityDurationUntilExhaustedCapacity',
-        'fillPool.start',
-        'fillPool.bailExhaustedCapacity'
-      );
-      return FillPoolResult.RanOutOfCapacity;
-    }
-    performance.mark('fillPool.cycle');
+  if ((await run(tasks)) === TaskPoolRunResult.RanOutOfCapacity) {
+    performance.mark('fillPool.bailExhaustedCapacity');
+    performance.measure(
+      'fillPool.activityDurationUntilExhaustedCapacity',
+      'fillPool.start',
+      'fillPool.bailExhaustedCapacity'
+    );
+    return FillPoolResult.RanOutOfCapacity;
   }
+  performance.mark('fillPool.cycle');
+  return FillPoolResult.PoolFilled;
 }