From 693541c1820008e69eb726e865f47bf26cbe55d8 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 15 Apr 2026 16:14:21 +0300
Subject: [PATCH] cgen: fix v generated shared .so crash on dlclose (fixes
 #15657)

---
 vlib/v/gen/c/cgen.v                                    | 6 ++++++
 vlib/v/gen/c/testdata/boehm_shared_startup.c.must_have | 1 +
 vlib/v/gen/c/testdata/boehm_shared_startup.vv          | 3 +++
 3 files changed, 10 insertions(+)
 create mode 100644 vlib/v/gen/c/testdata/boehm_shared_startup.c.must_have
 create mode 100644 vlib/v/gen/c/testdata/boehm_shared_startup.vv

diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 4b5b0bb69..68cf40e11 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -9239,6 +9239,12 @@ fn (mut g Gen) write_init_function() {
 		g.writeln('\tv__trace_calls__on_call(_S("_vinit"));')
 	}
 
+	if g.pref.is_shared
+		&& g.pref.gc_mode in [.boehm_full, .boehm_incr, .boehm_full_opt, .boehm_incr_opt, .boehm_leak] {
+		// Shared libraries can be unloaded while Boehm marker threads are still alive.
+		g.writeln('\tGC_set_markers_count(1);')
+	}
+
 	if g.use_segfault_handler && !g.pref.is_shared {
 		if _ := g.table.fns['v_segmentation_fault_handler'] {
 			// 11 is SIGSEGV. It is hardcoded here, to avoid FreeBSD compilation errors for trivial examples.
diff --git a/vlib/v/gen/c/testdata/boehm_shared_startup.c.must_have b/vlib/v/gen/c/testdata/boehm_shared_startup.c.must_have
new file mode 100644
index 000000000..532b2ea21
--- /dev/null
+++ b/vlib/v/gen/c/testdata/boehm_shared_startup.c.must_have
@@ -0,0 +1 @@
+GC_set_markers_count(1);
diff --git a/vlib/v/gen/c/testdata/boehm_shared_startup.vv b/vlib/v/gen/c/testdata/boehm_shared_startup.vv
new file mode 100644
index 000000000..7704bbf68
--- /dev/null
+++ b/vlib/v/gen/c/testdata/boehm_shared_startup.vv
@@ -0,0 +1,3 @@
+// vtest vflags: -gc boehm -shared
+@[export: 'noop']
+pub fn noop() {}
-- 
2.39.5