Merge pull request #12219 from Expensify/jasper-readPromiseSeqQueue

Make `API.read` wait on all requests on the SequentialQueue to respond

src/libs/API.js

@@ -105,7 +105,10 @@ function makeRequestWithSideEffects(command, apiCommandParameters = {}, onyxData
  * @param {Object} [onyxData.failureData] - Onyx instructions that will be passed to Onyx.update() when the response has jsonCode !== 200.
  */
 function read(command, apiCommandParameters, onyxData) {
-    makeRequestWithSideEffects(command, apiCommandParameters, onyxData, CONST.API_REQUEST_TYPE.READ);
+    // Ensure all write requests on the sequential queue have finished responding before running read requests.
+    // Responses from read requests can overwrite the optimistic data inserted by
+    // write requests that use the same Onyx keys and haven't responded yet.
+    SequentialQueue.waitForIdle().then(() => makeRequestWithSideEffects(command, apiCommandParameters, onyxData, CONST.API_REQUEST_TYPE.READ));
 }
 
 export {

src/libs/Network/SequentialQueue.js

@@ -114,9 +114,18 @@ function getCurrentRequest() {
     return currentRequest;
 }
 
+/**
+ * Returns a promise that resolves when the sequential queue is done processing all persisted write requests.
+ * @returns {Promise}
+ */
+function waitForIdle() {
+    return isReadyPromise;
+}
+
 export {
     flush,
     getCurrentRequest,
     isRunning,
     push,
+    waitForIdle,
 };