stbi: fix memory leak from stbi.load/1 with GC (#16028)

cmd/tools/vtest-all.v

@@ -263,6 +263,15 @@ fn get_all_commands() []Command {
 			rmfile: 'v.c'
 		}
 	}
+	$if linux {
+		res << Command{
+			line: '$vexe vlib/v/tests/bench/bench_stbi_load.v && prlimit -v10485760 vlib/v/tests/bench/bench_stbi_load'
+			okmsg: 'STBI load does not leak with GC on, when loading images multiple times (use < 10MB)'
+			runcmd: .execute
+			contains: 'logo.png 1000 times.'
+			rmfile: 'vlib/v/tests/bench/bench_stbi_load'
+		}
+	}
 	$if !windows {
 		res << Command{
 			line: '$vexe -raw-vsh-tmp-prefix tmp vlib/v/tests/script_with_no_extension'

thirdparty/stb_image/stbi.c

@@ -1,5 +1,19 @@
 #define STB_IMAGE_IMPLEMENTATION
 #define STB_IMAGE_WRITE_IMPLEMENTATION
+
+#include <stddef.h>
+
+extern void * stbi__callback_malloc(size_t size);
+extern void * stbi__callback_realloc(void *ptr, size_t size);
+extern void   stbi__callback_free(void *ptr);
+
+#define STBI_MALLOC(sz)           stbi__callback_malloc(sz)
+#define STBI_REALLOC(p,newsz)     stbi__callback_realloc(p,newsz)
+#define STBI_FREE(p)              stbi__callback_free(p)
+#define STBIW_MALLOC(sz)          stbi__callback_malloc(sz)
+#define STBIW_REALLOC(p,newsz)    stbi__callback_realloc(p,newsz)
+#define STBIW_FREE(p)             stbi__callback_free(p)
+
 #include "stb_image.h"
 #include "stb_image_write.h"
 
@@ -20,3 +34,4 @@ void write_force_png_filter(int level){
 void write_tga_with_rle(int level) {
 	stbi_write_tga_with_rle = level;
 }
+

vlib/stbi/stbi.c.v

@@ -4,6 +4,31 @@
 
 module stbi
 
+[if trace_stbi_allocations ?]
+fn trace_allocation(message string) {
+	eprintln(message)
+}
+
+[export: 'stbi__callback_malloc']
+fn cb_malloc(s usize) voidptr {
+	res := unsafe { malloc(isize(s)) }
+	trace_allocation('> stbi__callback_malloc: $s => ${ptr_str(res)}')
+	return res
+}
+
+[export: 'stbi__callback_realloc']
+fn cb_realloc(p voidptr, s usize) voidptr {
+	res := unsafe { v_realloc(p, isize(s)) }
+	trace_allocation('> stbi__callback_realloc: ${ptr_str(p)} , $s => ${ptr_str(res)}')
+	return res
+}
+
+[export: 'stbi__callback_free']
+fn cb_free(p voidptr) {
+	trace_allocation('> stbi__callback_free: ${ptr_str(p)}')
+	unsafe { free(p) }
+}
+
 #flag -I @VEXEROOT/thirdparty/stb_image
 #include "stb_image.h"
 #include "stb_image_write.h"

vlib/v/tests/bench/bench_stbi_load.v

@@ -0,0 +1,19 @@
+import os
+import stbi
+
+fn load_image(path string) {
+	img := stbi.load(path) or { return }
+	assert img.ok
+	// unsafe { img.free() }
+}
+
+fn main() {
+	pid := os.getpid()
+	image_path := os.args[1] or { '${@VEXEROOT}/examples/assets/logo.png' }
+	for i in 1 .. 1001 {
+		if i % 100 == 0 {
+			println('pid: $pid | Loaded $image_path $i times.')
+		}
+		load_image(image_path)
+	}
+}