crystal-gc-tweak.diff

diff --git a/src/gc/boehm.cr b/src/gc/boehm.cr
index bc05474..d692a28 100644
--- a/src/gc/boehm.cr
+++ b/src/gc/boehm.cr
@@ -16,6 +16,8 @@ lib LibGC
   type Finalizer = Void*, Void* ->
   fun register_finalizer = GC_register_finalizer(obj : Void*, fn : Finalizer, cd : Void*, ofn : Finalizer*, ocd : Void**)
   fun invoke_finalizers = GC_invoke_finalizers : Int32
+  fun set_finalize_on_demand = GC_set_finalize_on_demand(value : Int32)
+  fun get_finalize_on_demand = GC_get_finalize_on_demand : Int32
 
   fun get_heap_usage_safe = GC_get_heap_usage_safe(heap_size : LibC::SizeT*, free_bytes : LibC::SizeT*, unmapped_bytes : LibC::SizeT*, bytes_since_gc : LibC::SizeT*, total_bytes : LibC::SizeT*)
   fun set_max_heap_size = GC_set_max_heap_size(LibC::SizeT)
@@ -78,7 +80,12 @@ module GC
         ->(obj, data) {
           same_object = obj as T
           if same_object.responds_to?(:finalize)
+            old_finalize_on_demand = LibGC.get_finalize_on_demand
+            # Prevent nested finalize calls, triggered by potential
+            # memory (re)allocation operations in finalizers
+            LibGC.set_finalize_on_demand(1)
             same_object.finalize
+            LibGC.set_finalize_on_demand(old_finalize_on_demand)
           end
         }, nil, nil, nil)
       nil