From ad3f18f031a0bd897f756d66486c2bc0216794a1 Mon Sep 17 00:00:00 2001
From: "Jeff Washington (jwash)"
 <75863576+jeffwashington@users.noreply.github.com>
Date: Wed, 14 Jul 2021 19:04:55 -0500
Subject: [PATCH] fix race condition in bg file reader file error (#18682)

---
 runtime/src/shared_buffer_reader.rs | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/runtime/src/shared_buffer_reader.rs b/runtime/src/shared_buffer_reader.rs
index b52fab54fb..5bf7083661 100644
--- a/runtime/src/shared_buffer_reader.rs
+++ b/runtime/src/shared_buffer_reader.rs
@@ -186,6 +186,7 @@ impl SharedBufferBgReader {
         let mut max_bytes_read = 0;
         let mut wait_us = 0;
         let mut total_bytes = 0;
+        let mut error = SharedBufferReader::default_error();
         loop {
             if self.stop.load(Ordering::Relaxed) {
                 // unsure what error is most appropriate here.
@@ -234,9 +235,9 @@ impl SharedBufferBgReader {
                         bytes_read += size;
                         // loop to read some more. Underlying reader does not usually read all we ask for.
                     }
-                    Err(err) => {
+                    Err(mut err) => {
                         error_received = true;
-                        self.set_error(err);
+                        std::mem::swap(&mut error, &mut err);
                         break;
                     }
                 }
@@ -259,6 +260,8 @@ impl SharedBufferBgReader {
 
             if error_received {
                 // do not ask for more data from 'reader'. We got an error and saved all the data we got before the error.
+                // but, wait to set error until we have added our buffer to newly_read_data
+                self.set_error(error);
                 break;
             }
         }
@@ -692,10 +695,12 @@ pub mod tests {
         );
         // #2 will read valid bytes first and succeed, then get error
         let mut data = vec![0; sent.len()];
-        // this read should succeed because it was prior to error being received by bg reader
+        // this read should succeed because it is reading data prior to error being received by bg reader
         let expected_len = 1;
         for i in 0..sent.len() {
-            assert_eq!(reader2.read(&mut data[i..=i]).unwrap(), expected_len);
+            let len = reader2.read(&mut data[i..=i]);
+            assert!(len.is_ok(), "{:?}, progress: {}", len, i);
+            assert_eq!(len.unwrap(), expected_len, "progress: {}", i);
         }
         assert_eq!(sent, data);
         assert_eq!(