From f97d840f96592eca16e362574d5e27cf66fa974f Mon Sep 17 00:00:00 2001
From: Igor Ribeiro de Assis <igor.assis@gmail.com>
Date: Tue, 16 Mar 2021 21:46:22 +0100
Subject: [PATCH] Fix FutureStream memory usage (#17395) [backport:1.2]

(cherry picked from commit 9bb0e557497c6d66ef7bdcda765098fd0271726f)
---
 lib/pure/asyncstreams.nim | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/pure/asyncstreams.nim b/lib/pure/asyncstreams.nim
index 7ffde9c106..bd366f58d7 100644
--- a/lib/pure/asyncstreams.nim
+++ b/lib/pure/asyncstreams.nim
@@ -110,7 +110,11 @@ proc read*[T](future: FutureStream[T]): owned(Future[(bool, T)]) =
     resFut.complete(res)
 
     # If the saved callback isn't nil then let's call it.
-    if not savedCb.isNil: savedCb()
+    if not savedCb.isNil:
+      if fs.queue.len > 0:
+        savedCb()
+      else:
+        future.cb = savedCb
 
   if future.queue.len > 0 or future.finished:
     newCb(future)