From cd946c454113b3441442051204ef9ba68f4213d4 Mon Sep 17 00:00:00 2001
From: Calvin Rose <calsrose@gmail.com>
Date: Mon, 28 Sep 2026 17:35:18 -0500
Subject: [PATCH] Apply fix for threaded channels "eating" values.

Reported by @pepe with help from Claude.
---
 src/core/corelib.c   |  6 +++---
 src/core/ev.c        |  5 ++++-
 test/suite-ev2.janet | 13 +++++++++++++
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/core/corelib.c b/src/core/corelib.c
index cdaba373..556420ce 100644
--- a/src/core/corelib.c
+++ b/src/core/corelib.c
@@ -550,9 +550,9 @@ JANET_CORE_FN(janet_core_gensym,
 
 JANET_CORE_FN(janet_core_gccollect,
               "(gccollect)",
-              "Run garbage collection. You should probably not call this manually.") {
+              "Run the garbage collector to free unreachable values.") {
     (void) argv;
-    (void) argc;
+    janet_fixarity(argc, 0);
     janet_collect();
     return janet_wrap_nil();
 }
@@ -561,7 +561,7 @@ JANET_CORE_FN(janet_core_gcsetinterval,
               "(gcsetinterval interval)",
               "Set an integer number of bytes to allocate before running garbage collection. "
               "Low values for interval will be slower but use less memory. "
-              "High values will be faster but use more memory.") {
+              "High values will be faster but use more memory. Set to 0 to disable automatic collection.") {
     janet_fixarity(argc, 1);
     size_t s = janet_getsize(argv, 0);
     /* limit interval to 48 bits */
diff --git a/src/core/ev.c b/src/core/ev.c
index bd87460b..01077def 100644
--- a/src/core/ev.c
+++ b/src/core/ev.c
@@ -977,7 +977,10 @@ static void janet_thread_chan_cb(JanetEVGenericMessage msg) {
                 break;
             }
             if (!sent) {
-                janet_chan_unpack(channel, &x, 1);
+                if (channel->closed || janet_q_push_head(&channel->items, &x, sizeof(Janet))) {
+                    /* channel is closed or full. Otherwise, keep it. */
+                    janet_chan_unpack(channel, &x, 1);
+                }
             }
         } else {
             JanetChannelPending writer;
diff --git a/test/suite-ev2.janet b/test/suite-ev2.janet
index 24a2e0c8..99020f24 100644
--- a/test/suite-ev2.janet
+++ b/test/suite-ev2.janet
@@ -101,4 +101,17 @@
 (assert (deep= @"hello\nworld2\n" (slurp "tmp/out.txt")) "file threading 1")
 (assert (deep= @"world1\nabc\n" (slurp "tmp/out2.txt")) "file threading 2")
 
+# A value given to a threaded channel whose only waiting reader has since been
+# resumed by another select clause must be kept for the next reader.
+(def stale-tchan (ev/thread-chan 10))
+(def stale-pchan (ev/chan 10))
+(ev/spawn (ev/select stale-tchan stale-pchan))
+(ev/sleep 0)
+(ev/give stale-pchan 1)
+(ev/sleep 0)
+(ev/give stale-tchan 42)
+(ev/sleep 0.01)
+(assert (= 42 (try (ev/with-deadline 1 (ev/take stale-tchan)) ([_] nil)))
+        "value given to a threaded channel with a stale reader is kept")
+
 (end-suite)