Make mrb->arena variable sized. Use MRB_GC_FIXED_ARENA for old behavior.

You will not see "arena overflow" error anymore, but I encourage gem authors
to check your gems with MRB_GC_FIXED_ARENA to avoid memory broat.

include/mrbconf.h

@@ -59,6 +59,12 @@
 /* array size for parser buffer */
 //#define MRB_PARSER_BUF_SIZE 1024
 
+/* arena size */
+//#define MRB_GC_ARENA_SIZE 100
+
+/* fixed size GC arena */
+//#define MRB_GC_FIXED_ARENA
+
 /* -DDISABLE_XXXX to drop following features */
 //#define DISABLE_STDIO		/* use of stdio */
 

include/mruby.h

@@ -46,8 +46,8 @@ struct mrb_state;
 
 typedef void* (*mrb_allocf) (struct mrb_state *mrb, void*, size_t, void *ud);
 
-#ifndef MRB_ARENA_SIZE
-#define MRB_ARENA_SIZE 100
+#ifndef MRB_GC_ARENA_SIZE
+#define MRB_GC_ARENA_SIZE 100
 #endif
 
 typedef struct {
@@ -128,7 +128,12 @@ typedef struct mrb_state {
   struct heap_page *sweeps;
   struct heap_page *free_heaps;
   size_t live; /* count of live objects */
-  struct RBasic *arena[MRB_ARENA_SIZE];   /* GC protection array */
+#ifdef MRB_GC_FIXED_ARENA
+  struct RBasic *arena[MRB_GC_ARENA_SIZE]; /* GC protection array */
+#else
+  struct RBasic **arena;                   /* GC protection array */
+  int arena_capa;
+#endif
   int arena_idx;
 
   enum gc_state gc_state; /* state of gc */

src/gc.c

@@ -370,10 +370,16 @@ mrb_free_heap(mrb_state *mrb)
 static void
 gc_protect(mrb_state *mrb, struct RBasic *p)
 {
-  if (mrb->arena_idx >= MRB_ARENA_SIZE) {
+  if (mrb->arena_idx >= MRB_GC_ARENA_SIZE) {
+#ifdef MRB_GC_FIXED_ARENA
     /* arena overflow error */
-    mrb->arena_idx = MRB_ARENA_SIZE - 4; /* force room in arena */
+    mrb->arena_idx = MRB_GC_ARENA_SIZE - 4; /* force room in arena */
     mrb_raise(mrb, E_RUNTIME_ERROR, "arena overflow error");
+#else
+    /* extend arena */
+    mrb->arena_capa *= 1.5;
+    mrb->arena = (struct RBasic**)mrb_realloc(mrb, mrb->arena, sizeof(struct RBasic*)*mrb->arena_capa);
+#endif
   }
   mrb->arena[mrb->arena_idx++] = p;
 }
@@ -1041,6 +1047,20 @@ mrb_gc_arena_save(mrb_state *mrb)
 void
 mrb_gc_arena_restore(mrb_state *mrb, int idx)
 {
+#ifndef MRB_GC_FIXED_ARENA
+  int capa = mrb->arena_capa;
+
+  if (idx < capa / 2) {
+    capa *= 0.66;
+    if (capa < MRB_GC_ARENA_SIZE) {
+      capa = MRB_GC_ARENA_SIZE;
+    }
+    if (capa != mrb->arena_capa) {
+      mrb->arena = (struct RBasic**)mrb_realloc(mrb, mrb->arena, sizeof(struct RBasic*)*capa);
+      mrb->arena_capa = capa;
+    }
+  }
+#endif
   mrb->arena_idx = idx;
 }
 

src/state.c

@@ -42,6 +42,11 @@ mrb_open_allocf(mrb_allocf f, void *ud)
   mrb->allocf = f;
   mrb->current_white_part = MRB_GC_WHITE_A;
 
+#ifndef MRB_GC_FIXED_ARENA
+  mrb->arena = (struct RBasic**)mrb_malloc(mrb, sizeof(struct RBasic*)*MRB_GC_ARENA_SIZE);
+  mrb->arena_capa = MRB_GC_ARENA_SIZE;
+#endif
+
   mrb_init_heap(mrb);
   mrb->c = (struct mrb_context*)mrb_malloc(mrb, sizeof(struct mrb_context));
   *mrb->c = mrb_context_zero;
@@ -191,6 +196,9 @@ mrb_close(mrb_state *mrb)
   mrb_free_symtbl(mrb);
   mrb_free_heap(mrb);
   mrb_alloca_free(mrb);
+#ifndef MRB_GC_FIXED_ARENA
+  mrb_free(mrb, mrb->arena);
+#endif
   mrb_free(mrb, mrb);
 }