From 3c01f71d9e2b760cbbe567da90684af486731f95 Mon Sep 17 00:00:00 2001
From: Kevin O'Connor <kevin@koconnor.net>
Date: Wed, 24 Sep 2025 18:52:10 -0400
Subject: [PATCH] itersolve: Don't call trapq_check_sentinels() from
 itersolve_generate_steps()

Commit a89694ac changed the code to run itersolve_generate_steps()
from multiple threads simultaneously.  However,
trapq_check_sentinels() can modify the shared trapq object.  So,
calling it from multiple threads could introduce a race condition.

Move the call to trapq_check_sentinels() to steppersyncmgr_gen_steps()
to avoid the issue.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
---
 klippy/chelper/itersolve.c   |  1 -
 klippy/chelper/steppersync.c | 12 ++++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/klippy/chelper/itersolve.c b/klippy/chelper/itersolve.c
index 9b1206249..5b1683606 100644
--- a/klippy/chelper/itersolve.c
+++ b/klippy/chelper/itersolve.c
@@ -151,7 +151,6 @@ itersolve_generate_steps(struct stepper_kinematics *sk, struct stepcompress *sc
     sk->last_flush_time = flush_time;
     if (!sk->tq)
         return 0;
-    trapq_check_sentinels(sk->tq);
     struct move *m = list_first_entry(&sk->tq->moves, struct move, node);
     while (last_flush_time >= m->print_time + m->move_t)
         m = list_next_entry(m, node);
diff --git a/klippy/chelper/steppersync.c b/klippy/chelper/steppersync.c
index 4dede38fb..6b571f4b6 100644
--- a/klippy/chelper/steppersync.c
+++ b/klippy/chelper/steppersync.c
@@ -21,6 +21,7 @@
 #include "serialqueue.h" // struct queue_message
 #include "stepcompress.h" // stepcompress_flush
 #include "steppersync.h" // steppersync_alloc
+#include "trapq.h" // trapq_check_sentinels
 
 
 /****************************************************************
@@ -397,6 +398,17 @@ steppersyncmgr_gen_steps(struct steppersyncmgr *ssm, double flush_time
                          , double gen_steps_time, double clear_history_time)
 {
     struct steppersync *ss;
+    // Prepare trapqs for step generation
+    list_for_each_entry(ss, &ssm->ss_list, ssm_node) {
+        struct syncemitter *se;
+        list_for_each_entry(se, &ss->se_list, ss_node) {
+            if (!se->sc || !se->sk)
+                continue;
+            struct trapq *tq = itersolve_get_trapq(se->sk);
+            if (tq)
+                trapq_check_sentinels(tq);
+        }
+    }
     // Start step generation threads
     list_for_each_entry(ss, &ssm->ss_list, ssm_node) {
         uint64_t flush_clock = clock_from_time(&ss->ce, flush_time);