From 4084f7ebec63cf9b6a53f3a12df91bbf0c0a4161 Mon Sep 17 00:00:00 2001
From: K Pamnany <kpamnany@users.noreply.github.com>
Date: Fri, 8 Jul 2022 18:47:14 +0000
Subject: [PATCH] Add channel state checks to reduce exceptions

In channel iteration and in the `@sync` race check.
---
 base/channels.jl | 18 +++++++++++-------
 base/task.jl     | 24 +++++++++++++-----------
 2 files changed, 24 insertions(+), 18 deletions(-)

diff --git a/base/channels.jl b/base/channels.jl
index da7b1d24583ca..0cf3b8d799926 100644
--- a/base/channels.jl
+++ b/base/channels.jl
@@ -493,14 +493,18 @@ function show(io::IO, ::MIME"text/plain", c::Channel)
 end
 
 function iterate(c::Channel, state=nothing)
-    try
-        return (take!(c), nothing)
-    catch e
-        if isa(e, InvalidStateException) && e.state === :closed
-            return nothing
-        else
-            rethrow()
+    if isopen(c) || isready(c)
+        try
+            return (take!(c), nothing)
+        catch e
+            if isa(e, InvalidStateException) && e.state === :closed
+                return nothing
+            else
+                rethrow()
+            end
         end
+    else
+        return nothing
     end
 end
 
diff --git a/base/task.jl b/base/task.jl
index 22b9c81c95606..5601fea70a112 100644
--- a/base/task.jl
+++ b/base/task.jl
@@ -424,19 +424,21 @@ function sync_end(c::Channel{Any})
     # Capture all waitable objects scheduled after the end of `@sync` and
     # include them in the exception. This way, the user can check what was
     # scheduled by examining at the exception object.
-    local racy
-    for r in c
-        if !@isdefined(racy)
-            racy = []
+    if isready(c)
+        local racy
+        for r in c
+            if !@isdefined(racy)
+                racy = []
+            end
+            push!(racy, r)
         end
-        push!(racy, r)
-    end
-    if @isdefined(racy)
-        if !@isdefined(c_ex)
-            c_ex = CompositeException()
+        if @isdefined(racy)
+            if !@isdefined(c_ex)
+                c_ex = CompositeException()
+            end
+            # Since this is a clear programming error, show this exception first:
+            pushfirst!(c_ex, ScheduledAfterSyncException(racy))
         end
-        # Since this is a clear programming error, show this exception first:
-        pushfirst!(c_ex, ScheduledAfterSyncException(racy))
     end
 
     if @isdefined(c_ex)