diff --git a/ext/-test-/gvl/instrumentation/instrumentation/depend b/ext/-test-/gvl/instrumentation/instrumentation/depend
new file mode 100644
index 00000000000000..33366d5bb2aace
--- /dev/null
+++ b/ext/-test-/gvl/instrumentation/instrumentation/depend
@@ -0,0 +1,163 @@
+# AUTOGENERATED DEPENDENCIES START
+instrumentation.o: $(RUBY_EXTCONF_H)
+instrumentation.o: $(arch_hdrdir)/ruby/config.h
+instrumentation.o: $(hdrdir)/ruby/assert.h
+instrumentation.o: $(hdrdir)/ruby/atomic.h
+instrumentation.o: $(hdrdir)/ruby/backward.h
+instrumentation.o: $(hdrdir)/ruby/backward/2/assume.h
+instrumentation.o: $(hdrdir)/ruby/backward/2/attributes.h
+instrumentation.o: $(hdrdir)/ruby/backward/2/bool.h
+instrumentation.o: $(hdrdir)/ruby/backward/2/inttypes.h
+instrumentation.o: $(hdrdir)/ruby/backward/2/limits.h
+instrumentation.o: $(hdrdir)/ruby/backward/2/long_long.h
+instrumentation.o: $(hdrdir)/ruby/backward/2/stdalign.h
+instrumentation.o: $(hdrdir)/ruby/backward/2/stdarg.h
+instrumentation.o: $(hdrdir)/ruby/defines.h
+instrumentation.o: $(hdrdir)/ruby/intern.h
+instrumentation.o: $(hdrdir)/ruby/internal/anyargs.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/char.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/double.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/fixnum.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/gid_t.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/int.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/intptr_t.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/long.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/long_long.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/mode_t.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/off_t.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/pid_t.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/short.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/size_t.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/st_data_t.h
+instrumentation.o: $(hdrdir)/ruby/internal/arithmetic/uid_t.h
+instrumentation.o: $(hdrdir)/ruby/internal/assume.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/alloc_size.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/artificial.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/cold.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/const.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/constexpr.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/deprecated.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/diagnose_if.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/enum_extensibility.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/error.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/flag_enum.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/forceinline.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/format.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/maybe_unused.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/noalias.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/nodiscard.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/noexcept.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/noinline.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/nonnull.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/noreturn.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/pure.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/restrict.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/returns_nonnull.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/warning.h
+instrumentation.o: $(hdrdir)/ruby/internal/attr/weakref.h
+instrumentation.o: $(hdrdir)/ruby/internal/cast.h
+instrumentation.o: $(hdrdir)/ruby/internal/compiler_is.h
+instrumentation.o: $(hdrdir)/ruby/internal/compiler_is/apple.h
+instrumentation.o: $(hdrdir)/ruby/internal/compiler_is/clang.h
+instrumentation.o: $(hdrdir)/ruby/internal/compiler_is/gcc.h
+instrumentation.o: $(hdrdir)/ruby/internal/compiler_is/intel.h
+instrumentation.o: $(hdrdir)/ruby/internal/compiler_is/msvc.h
+instrumentation.o: $(hdrdir)/ruby/internal/compiler_is/sunpro.h
+instrumentation.o: $(hdrdir)/ruby/internal/compiler_since.h
+instrumentation.o: $(hdrdir)/ruby/internal/config.h
+instrumentation.o: $(hdrdir)/ruby/internal/constant_p.h
+instrumentation.o: $(hdrdir)/ruby/internal/core.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rarray.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rbasic.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rbignum.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rclass.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rdata.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rfile.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rhash.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/robject.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rregexp.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rstring.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rstruct.h
+instrumentation.o: $(hdrdir)/ruby/internal/core/rtypeddata.h
+instrumentation.o: $(hdrdir)/ruby/internal/ctype.h
+instrumentation.o: $(hdrdir)/ruby/internal/dllexport.h
+instrumentation.o: $(hdrdir)/ruby/internal/dosish.h
+instrumentation.o: $(hdrdir)/ruby/internal/error.h
+instrumentation.o: $(hdrdir)/ruby/internal/eval.h
+instrumentation.o: $(hdrdir)/ruby/internal/event.h
+instrumentation.o: $(hdrdir)/ruby/internal/fl_type.h
+instrumentation.o: $(hdrdir)/ruby/internal/gc.h
+instrumentation.o: $(hdrdir)/ruby/internal/glob.h
+instrumentation.o: $(hdrdir)/ruby/internal/globals.h
+instrumentation.o: $(hdrdir)/ruby/internal/has/attribute.h
+instrumentation.o: $(hdrdir)/ruby/internal/has/builtin.h
+instrumentation.o: $(hdrdir)/ruby/internal/has/c_attribute.h
+instrumentation.o: $(hdrdir)/ruby/internal/has/cpp_attribute.h
+instrumentation.o: $(hdrdir)/ruby/internal/has/declspec_attribute.h
+instrumentation.o: $(hdrdir)/ruby/internal/has/extension.h
+instrumentation.o: $(hdrdir)/ruby/internal/has/feature.h
+instrumentation.o: $(hdrdir)/ruby/internal/has/warning.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/array.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/bignum.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/class.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/compar.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/complex.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/cont.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/dir.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/enum.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/enumerator.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/error.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/eval.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/file.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/gc.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/hash.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/io.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/load.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/marshal.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/numeric.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/object.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/parse.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/proc.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/process.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/random.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/range.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/rational.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/re.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/ruby.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/select.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/select/largesize.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/signal.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/sprintf.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/string.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/struct.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/thread.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/time.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/variable.h
+instrumentation.o: $(hdrdir)/ruby/internal/intern/vm.h
+instrumentation.o: $(hdrdir)/ruby/internal/interpreter.h
+instrumentation.o: $(hdrdir)/ruby/internal/iterator.h
+instrumentation.o: $(hdrdir)/ruby/internal/memory.h
+instrumentation.o: $(hdrdir)/ruby/internal/method.h
+instrumentation.o: $(hdrdir)/ruby/internal/module.h
+instrumentation.o: $(hdrdir)/ruby/internal/newobj.h
+instrumentation.o: $(hdrdir)/ruby/internal/rgengc.h
+instrumentation.o: $(hdrdir)/ruby/internal/scan_args.h
+instrumentation.o: $(hdrdir)/ruby/internal/special_consts.h
+instrumentation.o: $(hdrdir)/ruby/internal/static_assert.h
+instrumentation.o: $(hdrdir)/ruby/internal/stdalign.h
+instrumentation.o: $(hdrdir)/ruby/internal/stdbool.h
+instrumentation.o: $(hdrdir)/ruby/internal/symbol.h
+instrumentation.o: $(hdrdir)/ruby/internal/value.h
+instrumentation.o: $(hdrdir)/ruby/internal/value_type.h
+instrumentation.o: $(hdrdir)/ruby/internal/variable.h
+instrumentation.o: $(hdrdir)/ruby/internal/warning_push.h
+instrumentation.o: $(hdrdir)/ruby/internal/xmalloc.h
+instrumentation.o: $(hdrdir)/ruby/missing.h
+instrumentation.o: $(hdrdir)/ruby/ruby.h
+instrumentation.o: $(hdrdir)/ruby/st.h
+instrumentation.o: $(hdrdir)/ruby/subst.h
+instrumentation.o: $(hdrdir)/ruby/thread.h
+instrumentation.o: $(hdrdir)/ruby/thread_native.h
+instrumentation.o: instrumentation.c
+# AUTOGENERATED DEPENDENCIES END
diff --git a/ext/-test-/gvl/instrumentation/instrumentation/extconf.rb b/ext/-test-/gvl/instrumentation/instrumentation/extconf.rb
new file mode 100644
index 00000000000000..81845048b23816
--- /dev/null
+++ b/ext/-test-/gvl/instrumentation/instrumentation/extconf.rb
@@ -0,0 +1,2 @@
+# frozen_string_literal: false
+create_makefile("-test-/gvl/instrumentation")
diff --git a/ext/-test-/gvl/instrumentation/instrumentation/instrumentation.c b/ext/-test-/gvl/instrumentation/instrumentation/instrumentation.c
new file mode 100644
index 00000000000000..a7c72cc2371604
--- /dev/null
+++ b/ext/-test-/gvl/instrumentation/instrumentation/instrumentation.c
@@ -0,0 +1,95 @@
+#include "ruby/ruby.h"
+#include "ruby/atomic.h"
+#include "ruby/thread.h"
+#include "ruby/thread_native.h"
+
+static rb_atomic_t acquire_enter_count = 0;
+static rb_atomic_t acquire_exit_count = 0;
+static rb_atomic_t release_count = 0;
+
+void
+ex_callback(rb_event_flag_t event, gvl_hook_event_args_t args)
+{
+    switch(event) {
+      case RUBY_INTERNAL_EVENT_GVL_ACQUIRE_ENTER:
+        RUBY_ATOMIC_INC(acquire_enter_count);
+        break;
+      case RUBY_INTERNAL_EVENT_GVL_ACQUIRE_EXIT:
+        RUBY_ATOMIC_INC(acquire_exit_count);
+        break;
+      case RUBY_INTERNAL_EVENT_GVL_RELEASE:
+        RUBY_ATOMIC_INC(release_count);
+        break;
+    }
+}
+
+static gvl_hook_t * single_hook = NULL;
+
+static VALUE
+thread_counters(VALUE thread)
+{
+    VALUE array = rb_ary_new2(3);
+    rb_ary_push(array, UINT2NUM(acquire_enter_count));
+    rb_ary_push(array, UINT2NUM(acquire_exit_count));
+    rb_ary_push(array, UINT2NUM(release_count));
+    return array;
+}
+
+static VALUE
+thread_reset_counters(VALUE thread)
+{
+    RUBY_ATOMIC_SET(acquire_enter_count, 0);
+    RUBY_ATOMIC_SET(acquire_exit_count, 0);
+    RUBY_ATOMIC_SET(release_count, 0);
+    return Qtrue;
+}
+
+static VALUE
+thread_register_gvl_callback(VALUE thread)
+{
+    single_hook = rb_gvl_event_new(
+        *ex_callback,
+        RUBY_INTERNAL_EVENT_GVL_ACQUIRE_ENTER | RUBY_INTERNAL_EVENT_GVL_ACQUIRE_EXIT | RUBY_INTERNAL_EVENT_GVL_RELEASE
+    );
+
+    return Qnil;
+}
+
+static VALUE
+thread_unregister_gvl_callback(VALUE thread)
+{
+    if (single_hook) {
+        rb_gvl_event_delete(single_hook);
+        single_hook = NULL;
+    }
+
+    return Qnil;
+}
+
+static VALUE
+thread_register_and_unregister_gvl_callback(VALUE thread)
+{
+    gvl_hook_t * hooks[5];
+    for (int i = 0; i < 5; i++) {
+        hooks[i] = rb_gvl_event_new(*ex_callback, RUBY_INTERNAL_EVENT_GVL_ACQUIRE_ENTER);
+    }
+
+    if (!rb_gvl_event_delete(hooks[4])) return Qfalse;
+    if (!rb_gvl_event_delete(hooks[0])) return Qfalse;
+    if (!rb_gvl_event_delete(hooks[3])) return Qfalse;
+    if (!rb_gvl_event_delete(hooks[2])) return Qfalse;
+    if (!rb_gvl_event_delete(hooks[1])) return Qfalse;
+    return Qtrue;
+}
+
+void
+Init_instrumentation(void)
+{
+    VALUE mBug = rb_define_module("Bug");
+    VALUE klass = rb_define_module_under(mBug, "GVLInstrumentation");
+    rb_define_singleton_method(klass, "counters", thread_counters, 0);
+    rb_define_singleton_method(klass, "reset_counters", thread_reset_counters, 0);
+    rb_define_singleton_method(klass, "register_callback", thread_register_gvl_callback, 0);
+    rb_define_singleton_method(klass, "unregister_callback", thread_unregister_gvl_callback, 0);
+    rb_define_singleton_method(klass, "register_and_unregister_callbacks", thread_register_and_unregister_gvl_callback, 0);
+}
diff --git a/include/ruby/internal/event.h b/include/ruby/internal/event.h
index 04b137a1939e85..633d17fa9e0541 100644
--- a/include/ruby/internal/event.h
+++ b/include/ruby/internal/event.h
@@ -82,18 +82,22 @@
  *
  * @{
  */
-#define RUBY_INTERNAL_EVENT_SWITCH          0x040000 /**< Thread switched. */
-#define RUBY_EVENT_SWITCH                   0x040000 /**< @old{RUBY_INTERNAL_EVENT_SWITCH} */
-                                         /* 0x080000 */
-#define RUBY_INTERNAL_EVENT_NEWOBJ          0x100000 /**< Object allocated. */
-#define RUBY_INTERNAL_EVENT_FREEOBJ         0x200000 /**< Object swept. */
-#define RUBY_INTERNAL_EVENT_GC_START        0x400000 /**< GC started. */
-#define RUBY_INTERNAL_EVENT_GC_END_MARK     0x800000 /**< GC ended mark phase. */
-#define RUBY_INTERNAL_EVENT_GC_END_SWEEP   0x1000000 /**< GC ended sweep phase. */
-#define RUBY_INTERNAL_EVENT_GC_ENTER       0x2000000 /**< `gc_enter()` is called. */
-#define RUBY_INTERNAL_EVENT_GC_EXIT        0x4000000 /**< `gc_exit()` is called. */
-#define RUBY_INTERNAL_EVENT_OBJSPACE_MASK  0x7f00000 /**< Bitmask of GC events. */
-#define RUBY_INTERNAL_EVENT_MASK          0xffff0000 /**< Bitmask of internal events. */
+#define RUBY_INTERNAL_EVENT_SWITCH             0x00040000 /**< Thread switched. */
+#define RUBY_EVENT_SWITCH                      0x00040000 /**< @old{RUBY_INTERNAL_EVENT_SWITCH} */
+                                             /*0x00080000 */
+#define RUBY_INTERNAL_EVENT_NEWOBJ             0x00100000 /**< Object allocated. */
+#define RUBY_INTERNAL_EVENT_FREEOBJ            0x00200000 /**< Object swept. */
+#define RUBY_INTERNAL_EVENT_GC_START           0x00400000 /**< GC started. */
+#define RUBY_INTERNAL_EVENT_GC_END_MARK        0x00800000 /**< GC ended mark phase. */
+#define RUBY_INTERNAL_EVENT_GC_END_SWEEP       0x01000000 /**< GC ended sweep phase. */
+#define RUBY_INTERNAL_EVENT_GC_ENTER           0x02000000 /**< `gc_enter()` is called. */
+#define RUBY_INTERNAL_EVENT_GC_EXIT            0x04000000 /**< `gc_exit()` is called. */
+#define RUBY_INTERNAL_EVENT_OBJSPACE_MASK      0x07f00000 /**< Bitmask of GC events. */
+#define RUBY_INTERNAL_EVENT_GVL_ACQUIRE_ENTER  0x10000000 /** `gvl_acquire() is called */
+#define RUBY_INTERNAL_EVENT_GVL_ACQUIRE_EXIT   0x20000000 /** `gvl_acquire() is exiting successfully */
+#define RUBY_INTERNAL_EVENT_GVL_RELEASE        0x40000000 /** `gvl_release() is called */
+#define RUBY_INTERNAL_EVENT_GVL_MASK           0x70000000 /**< Bitmask of GVL events. */
+#define RUBY_INTERNAL_EVENT_MASK               0xffff0000 /**< Bitmask of internal events. */
 
 /** @} */
 
diff --git a/include/ruby/thread_native.h b/include/ruby/thread_native.h
index c23b15e133a81f..7c4b24273fc685 100644
--- a/include/ruby/thread_native.h
+++ b/include/ruby/thread_native.h
@@ -201,5 +201,20 @@ void rb_native_cond_initialize(rb_nativethread_cond_t *cond);
  */
 void rb_native_cond_destroy(rb_nativethread_cond_t *cond);
 
+typedef struct gvl_hook_event_args {
+    unsigned long waiting;
+} gvl_hook_event_args_t;
+
+typedef void (*rb_gvl_callback)(uint32_t event, gvl_hook_event_args_t args);
+
+typedef struct gvl_hook {
+    rb_gvl_callback callback;
+    rb_event_flag_t event;
+
+    struct gvl_hook *next;
+} gvl_hook_t;
+
+gvl_hook_t * rb_gvl_event_new(rb_gvl_callback callback, rb_event_flag_t event);
+bool rb_gvl_event_delete(gvl_hook_t * hook);
 RBIMPL_SYMBOL_EXPORT_END()
 #endif
diff --git a/test/-ext-/gvl/test_instrumentation_api.rb b/test/-ext-/gvl/test_instrumentation_api.rb
new file mode 100644
index 00000000000000..e93df2becfbbee
--- /dev/null
+++ b/test/-ext-/gvl/test_instrumentation_api.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: false
+class TestGVLInstrumentation < Test::Unit::TestCase
+  def setup
+    pend("TODO: No windows support yet") if /mswin|mingw|bccwin/ =~ RUBY_PLATFORM
+  end
+
+  def test_gvl_instrumentation
+    require '-test-/gvl/instrumentation'
+    Bug::GVLInstrumentation.reset_counters
+    Bug::GVLInstrumentation::register_callback
+
+    begin
+      threads = 5.times.map { Thread.new { sleep 0.05; 1 + 1; sleep 0.02 } }
+      threads.each(&:join)
+      Bug::GVLInstrumentation.counters.each do |c|
+        assert_predicate c,:nonzero?
+      end
+    ensure
+      Bug::GVLInstrumentation::unregister_callback
+    end
+  end
+
+  def test_gvl_instrumentation_fork_safe
+    skip "No fork()" unless Process.respond_to?(:fork)
+
+    require '-test-/gvl/instrumentation'
+    Bug::GVLInstrumentation::register_callback
+
+    begin
+      pid = fork do
+        Bug::GVLInstrumentation.reset_counters
+        threads = 5.times.map { Thread.new { sleep 0.05; 1 + 1; sleep 0.02 } }
+        threads.each(&:join)
+        Bug::GVLInstrumentation.counters.each do |c|
+          assert_predicate c,:nonzero?
+        end
+      end
+      _, status = Process.wait2(pid)
+      assert_predicate status, :success?
+    ensure
+      Bug::GVLInstrumentation::unregister_callback
+    end
+  end
+
+  def test_gvl_instrumentation_unregister
+    require '-test-/gvl/instrumentation'
+    assert Bug::GVLInstrumentation::register_and_unregister_callbacks
+  end
+end
+
diff --git a/thread_pthread.c b/thread_pthread.c
index 55289de73a3be4..2e581a10a81c28 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -101,6 +101,83 @@
 #  endif
 #endif
 
+static gvl_hook_t * rb_gvl_hooks = NULL;
+static pthread_rwlock_t rb_gvl_hooks_rw_lock = PTHREAD_RWLOCK_INITIALIZER;
+
+gvl_hook_t *
+rb_gvl_event_new(rb_gvl_callback callback, rb_event_flag_t event) {
+    gvl_hook_t *hook = ALLOC_N(gvl_hook_t, 1);
+    hook->callback = callback;
+    hook->event = event;
+
+    int r;
+    if ((r = pthread_rwlock_wrlock(&rb_gvl_hooks_rw_lock))) {
+        rb_bug_errno("pthread_rwlock_wrlock", r);
+    }
+
+    hook->next = rb_gvl_hooks;
+    ATOMIC_PTR_EXCHANGE(rb_gvl_hooks, hook);
+
+    if ((r = pthread_rwlock_unlock(&rb_gvl_hooks_rw_lock))) {
+        rb_bug_errno("pthread_rwlock_unlock", r);
+    }
+    return hook;
+}
+
+bool
+rb_gvl_event_delete(gvl_hook_t * hook) {
+    int r;
+    if ((r = pthread_rwlock_wrlock(&rb_gvl_hooks_rw_lock))) {
+        rb_bug_errno("pthread_rwlock_wrlock", r);
+    }
+
+    bool success = FALSE;
+
+    if (rb_gvl_hooks == hook) {
+        ATOMIC_PTR_EXCHANGE(rb_gvl_hooks, hook->next);
+        success = TRUE;
+    } else {
+        gvl_hook_t *h = rb_gvl_hooks;
+
+        do {
+            if (h->next == hook) {
+                h->next = hook->next;
+                success = TRUE;
+            }
+        } while ((h = h->next));
+    }
+
+    if ((r = pthread_rwlock_unlock(&rb_gvl_hooks_rw_lock))) {
+        rb_bug_errno("pthread_rwlock_unlock", r);
+    }
+
+    if (success) {
+        ruby_xfree(hook);
+    }
+    return success;
+}
+
+static void
+rb_gvl_execute_hooks(rb_event_flag_t event, rb_atomic_t waiting) {
+    int r;
+    if ((r = pthread_rwlock_rdlock(&rb_gvl_hooks_rw_lock))) {
+        rb_bug_errno("pthread_rwlock_rdlock", r);
+    }
+
+    if (rb_gvl_hooks) {
+        gvl_hook_t *h = rb_gvl_hooks;
+        gvl_hook_event_args_t args = { .waiting = waiting };
+        do {
+            if (h->event & event) {
+                (*h->callback)(event, args);
+            }
+        } while((h = h->next));
+    }
+    if ((r = pthread_rwlock_unlock(&rb_gvl_hooks_rw_lock))) {
+        rb_bug_errno("pthread_rwlock_unlock", r);
+    }
+}
+
 enum rtimer_state {
     /* alive, after timer_create: */
     RTIMER_DISARM,
@@ -290,6 +367,10 @@ gvl_acquire_common(rb_global_vm_lock_t *gvl, rb_thread_t *th)
 	          "we must not be in ubf_list and GVL waitq at the same time");
 
         list_add_tail(&gvl->waitq, &nd->node.gvl);
+        ATOMIC_INC(gvl->waiting);
+        if (rb_gvl_hooks) {
+            rb_gvl_execute_hooks(RUBY_INTERNAL_EVENT_GVL_ACQUIRE_ENTER, gvl->waiting);
+        }
 
         do {
             if (!gvl->timer) {
@@ -301,6 +382,7 @@ gvl_acquire_common(rb_global_vm_lock_t *gvl, rb_thread_t *th)
         } while (gvl->owner);
 
         list_del_init(&nd->node.gvl);
+        ATOMIC_DEC(gvl->waiting);
 
         if (gvl->need_yield) {
             gvl->need_yield = 0;
@@ -311,6 +393,11 @@ gvl_acquire_common(rb_global_vm_lock_t *gvl, rb_thread_t *th)
         gvl->timer_err = ETIMEDOUT;
     }
     gvl->owner = th;
+
+    if (rb_gvl_hooks) {
+        rb_gvl_execute_hooks(RUBY_INTERNAL_EVENT_GVL_ACQUIRE_EXIT, gvl->waiting);
+    }
+
     if (!gvl->timer) {
         if (!designate_timer_thread(gvl) && !ubf_threads_empty()) {
             rb_thread_wakeup_timer_thread(-1);
@@ -329,6 +416,10 @@ gvl_acquire(rb_global_vm_lock_t *gvl, rb_thread_t *th)
 static const native_thread_data_t *
 gvl_release_common(rb_global_vm_lock_t *gvl)
 {
+    if (rb_gvl_hooks) {
+        rb_gvl_execute_hooks(RUBY_INTERNAL_EVENT_GVL_RELEASE, gvl->waiting);
+    }
+
     native_thread_data_t *next;
     gvl->owner = 0;
     next = list_top(&gvl->waitq, native_thread_data_t, node.ubf);
@@ -390,6 +481,7 @@ rb_gvl_init(rb_global_vm_lock_t *gvl)
     rb_native_cond_initialize(&gvl->switch_wait_cond);
     list_head_init(&gvl->waitq);
     gvl->owner = 0;
+    gvl->waiting = 0;
     gvl->timer = 0;
     gvl->timer_err = ETIMEDOUT;
     gvl->need_yield = 0;
@@ -644,9 +736,14 @@ static void native_thread_init(rb_thread_t *th);
 void
 Init_native_thread(rb_thread_t *th)
 {
+    int r;
+    if ((r = pthread_rwlock_init(&rb_gvl_hooks_rw_lock, NULL))) {
+        rb_bug_errno("pthread_rwlock_init", r);
+    }
+
 #if defined(HAVE_PTHREAD_CONDATTR_SETCLOCK)
     if (condattr_monotonic) {
-        int r = pthread_condattr_init(condattr_monotonic);
+        r = pthread_condattr_init(condattr_monotonic);
         if (r == 0) {
             r = pthread_condattr_setclock(condattr_monotonic, CLOCK_MONOTONIC);
         }
diff --git a/thread_pthread.h b/thread_pthread.h
index 2ac354046c010b..1b38a6d34cedbc 100644
--- a/thread_pthread.h
+++ b/thread_pthread.h
@@ -59,6 +59,7 @@ typedef struct rb_global_vm_lock_struct {
      *   timer.
      */
     struct list_head waitq; /* <=> native_thread_data_t.node.ubf */
+    rb_atomic_t waiting;
     const struct rb_thread_struct *timer;
     int timer_err;
 
diff --git a/thread_win32.c b/thread_win32.c
index 9b44ceb96a9e4a..6838820084aa36 100644
--- a/thread_win32.c
+++ b/thread_win32.c
@@ -35,6 +35,16 @@ static volatile DWORD ruby_native_thread_key = TLS_OUT_OF_INDEXES;
 
 static int w32_wait_events(HANDLE *events, int count, DWORD timeout, rb_thread_t *th);
 
+gvl_hook_t *
+rb_gvl_event_new(rb_gvl_callback callback, rb_event_flag_t event) {
+    // not implemented yet
+}
+
+bool
+rb_gvl_event_delete(gvl_hook_t * hook) {
+    // not implemented yet
+}
+
 RBIMPL_ATTR_NORETURN()
 static void
 w32_error(const char *func)