slightly better way to handle makeExclusiveReturning

Author: rlindner81

src/shared/semaphore.js

@@ -72,17 +72,19 @@ class Semaphore {
 
   /**
    * Take an async function and turn it into an exclusively executing async function. Calls during async execution will
-   * be returned.
+   * get a promise for the result of the exclusive caller.
    */
   static makeExclusiveReturning(cb) {
     let isRunning;
+    let runningPromise;
     return async (...args) => {
       if (isRunning) {
-        return;
+        return runningPromise;
       }
       isRunning = true;
       try {
-        return await cb(...args);
+        runningPromise = cb(...args);
+        return await runningPromise;
       } finally {
         isRunning = false;
       }

test/shared/semaphore.test.js

@@ -9,12 +9,11 @@ describe("semaphore", () => {
   let executionLog;
   const n = 3;
   const m = 2;
-  const result = "finished";
   const runner = async (index) => {
     executionLog.push(format("started %d", index));
     await sleep(10);
     executionLog.push(format("finished %d", index));
-    return result;
+    return format("result %d", index);
   };
 
   beforeEach(() => {
@@ -27,15 +26,15 @@ describe("semaphore", () => {
     const resultsSecondary = await Promise.all(Array.from({ length: m }, (_, i) => runner(n + i + 1)));
     expect(resultsPrimary).toMatchInlineSnapshot(`
       [
-        "finished",
-        "finished",
-        "finished",
+        "result 1",
+        "result 2",
+        "result 3",
       ]
     `);
     expect(resultsSecondary).toMatchInlineSnapshot(`
       [
-        "finished",
-        "finished",
+        "result 4",
+        "result 5",
       ]
     `);
     expect(executionLog).toMatchInlineSnapshot(`
@@ -61,15 +60,15 @@ describe("semaphore", () => {
     const resultsSecondary = await Promise.all(Array.from({ length: m }, (_, i) => exclusiveRunner(n + i + 1)));
     expect(resultsPrimary).toMatchInlineSnapshot(`
       [
-        "finished",
-        "finished",
-        "finished",
+        "result 1",
+        "result 2",
+        "result 3",
       ]
     `);
     expect(resultsSecondary).toMatchInlineSnapshot(`
       [
-        "finished",
-        "finished",
+        "result 4",
+        "result 5",
       ]
     `);
     expect(executionLog).toMatchInlineSnapshot(`
@@ -95,15 +94,15 @@ describe("semaphore", () => {
     const resultsSecondary = await Promise.all(Array.from({ length: m }, (_, i) => exclusiveRunner(n + i + 1)));
     expect(resultsPrimary).toMatchInlineSnapshot(`
       [
-        "finished",
-        undefined,
-        undefined,
+        "result 1",
+        "result 1",
+        "result 1",
       ]
     `);
     expect(resultsSecondary).toMatchInlineSnapshot(`
       [
-        "finished",
-        undefined,
+        "result 4",
+        "result 4",
       ]
     `);
     expect(executionLog).toMatchInlineSnapshot(`