From 9da21771eb11287d455f40a98c5b24e97c48a0f9 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 11 Mar 2026 12:35:48 +0300
Subject: [PATCH] cgen: the gc makes the apps run slow at first (fixes #24827)

---
 vlib/v/gen/c/cmain.v                          | 78 ++++++++++++-------
 .../boehm_default_startup.c.must_have         |  2 +
 .../v/gen/c/testdata/boehm_default_startup.vv |  2 +
 3 files changed, 56 insertions(+), 26 deletions(-)
 create mode 100644 vlib/v/gen/c/testdata/boehm_default_startup.c.must_have
 create mode 100644 vlib/v/gen/c/testdata/boehm_default_startup.vv

diff --git a/vlib/v/gen/c/cmain.v b/vlib/v/gen/c/cmain.v
index f162d84c6..1c0caf9ee 100644
--- a/vlib/v/gen/c/cmain.v
+++ b/vlib/v/gen/c/cmain.v
@@ -148,32 +148,26 @@ fn (mut g Gen) gen_c_main_function_header() {
 	}
 }
 
-fn (mut g Gen) gen_boehm_gc_init() {
-	g.writeln('#if defined(_VGCBOEHM)')
-	if g.pref.gc_mode == .boehm_leak {
-		g.writeln('\tGC_set_find_leak(1);')
-	}
-	if g.pref.os == .linux && !g.pref.no_builtin {
-		g.writeln('\tbool __v_gc_debugger_workaround = builtin__gc_prepare_for_debugger_init();')
-	}
-	g.writeln('\tGC_set_pages_executable(0);')
-	if g.pref.use_coroutines {
-		g.writeln('\tGC_allow_register_threads();')
-	}
-	g.writeln('\tGC_INIT();')
-	if g.pref.os == .linux && !g.pref.no_builtin {
-		g.writeln('\tbuiltin__gc_restore_roots_after_debugger_init(__v_gc_debugger_workaround);')
-	}
-	if g.pref.gc_mode in [.boehm_incr, .boehm_incr_opt] {
-		g.writeln('\tGC_enable_incremental();')
-	}
-	g.writeln('#endif')
-}
-
 fn (mut g Gen) gen_c_main_header() {
 	g.gen_c_main_function_header()
 	if g.pref.gc_mode in [.boehm_full, .boehm_incr, .boehm_full_opt, .boehm_incr_opt, .boehm_leak] {
-		g.gen_boehm_gc_init()
+		g.writeln('#if defined(_VGCBOEHM)')
+		if g.pref.gc_mode == .boehm_leak {
+			g.writeln('\tGC_set_find_leak(1);')
+		}
+		g.writeln('\tGC_set_pages_executable(0);')
+		if g.pref.gc_mode in [.boehm_full_opt, .boehm_incr_opt] {
+			g.writeln('\tGC_set_free_space_divisor(2);')
+		}
+		if g.pref.use_coroutines {
+			g.writeln('\tGC_allow_register_threads();')
+		}
+		g.writeln('\tGC_INIT();')
+
+		if g.pref.gc_mode in [.boehm_incr, .boehm_incr_opt] {
+			g.writeln('\tGC_enable_incremental();')
+		}
+		g.writeln('#endif')
 	}
 	if g.pref.gc_mode == .vgc {
 		g.writeln('\tbuiltin__vgc_init();')
@@ -222,7 +216,19 @@ sapp_desc sokol_main(int argc, char* argv[]) {
 	g.gen_c_main_trace_calls_hook()
 
 	if g.pref.gc_mode in [.boehm_full, .boehm_incr, .boehm_full_opt, .boehm_incr_opt, .boehm_leak] {
-		g.gen_boehm_gc_init()
+		g.writeln('#if defined(_VGCBOEHM)')
+		if g.pref.gc_mode == .boehm_leak {
+			g.writeln('\tGC_set_find_leak(1);')
+		}
+		g.writeln('\tGC_set_pages_executable(0);')
+		if g.pref.gc_mode in [.boehm_full_opt, .boehm_incr_opt] {
+			g.writeln('\tGC_set_free_space_divisor(2);')
+		}
+		g.writeln('\tGC_INIT();')
+		if g.pref.gc_mode in [.boehm_incr, .boehm_incr_opt] {
+			g.writeln('\tGC_enable_incremental();')
+		}
+		g.writeln('#endif')
 	}
 	if g.pref.gc_mode == .vgc {
 		g.writeln('\tbuiltin__vgc_init();')
@@ -299,7 +305,22 @@ pub fn (mut g Gen) gen_c_main_for_tests() {
 	g.writeln('')
 	g.gen_c_main_function_header()
 	if g.pref.gc_mode in [.boehm_full, .boehm_incr, .boehm_full_opt, .boehm_incr_opt, .boehm_leak] {
-		g.gen_boehm_gc_init()
+		g.writeln('#if defined(_VGCBOEHM)')
+		if g.pref.gc_mode == .boehm_leak {
+			g.writeln('\tGC_set_find_leak(1);')
+		}
+		g.writeln('\tGC_set_pages_executable(0);')
+		if g.pref.gc_mode in [.boehm_full_opt, .boehm_incr_opt] {
+			g.writeln('\tGC_set_free_space_divisor(2);')
+		}
+		if g.pref.use_coroutines {
+			g.writeln('\tGC_allow_register_threads();')
+		}
+		g.writeln('\tGC_INIT();')
+		if g.pref.gc_mode in [.boehm_incr, .boehm_incr_opt] {
+			g.writeln('\tGC_enable_incremental();')
+		}
+		g.writeln('#endif')
 	}
 	if g.pref.gc_mode == .vgc {
 		g.writeln('\tbuiltin__vgc_init();')
@@ -398,12 +419,17 @@ pub fn (mut g Gen) gen_c_main_trace_calls_hook() {
 
 // gen_dll_main create DllMain() for windows .dll.
 pub fn (mut g Gen) gen_dll_main() {
+	opt_gc_setup := if g.pref.gc_mode in [.boehm_full_opt, .boehm_incr_opt] {
+		'\t\t\tGC_set_free_space_divisor(2);\n'
+	} else {
+		''
+	}
 	g.writeln('VV_EXP BOOL DllMain(HINSTANCE hinst,DWORD fdwReason,LPVOID lpvReserved) {
 	switch (fdwReason) {
 		case DLL_PROCESS_ATTACH : {
 #if defined(_VGCBOEHM)
 			GC_set_pages_executable(0);
-			GC_INIT();
+${opt_gc_setup}			GC_INIT();
 #endif
 			_vinit_caller();
 			break;
diff --git a/vlib/v/gen/c/testdata/boehm_default_startup.c.must_have b/vlib/v/gen/c/testdata/boehm_default_startup.c.must_have
new file mode 100644
index 000000000..1122b4253
--- /dev/null
+++ b/vlib/v/gen/c/testdata/boehm_default_startup.c.must_have
@@ -0,0 +1,2 @@
+GC_set_free_space_divisor(2);
+GC_INIT();
diff --git a/vlib/v/gen/c/testdata/boehm_default_startup.vv b/vlib/v/gen/c/testdata/boehm_default_startup.vv
new file mode 100644
index 000000000..9f25395d5
--- /dev/null
+++ b/vlib/v/gen/c/testdata/boehm_default_startup.vv
@@ -0,0 +1,2 @@
+// vtest vflags: -gc boehm
+fn main() {}
-- 
2.39.5