I think its a fence class

rendering_api/metal/src/core/sync/fence/metal_fence.h

@@ -0,0 +1,10 @@
+#pragma once
+#include "core/sync/fence/gryphn_fence.h"
+#import <Metal/Metal.h>
+#import <Metal/MTLEvent.h>
+
+typedef struct gnPlatformFence_t {
+    id<MTLSharedEvent> fence;
+    MTLSharedEventListener* listener;
+    dispatch_semaphore_t semaphore;
+} gnPlatformFence;

rendering_api/metal/src/core/sync/fence/metal_fence.m

@@ -0,0 +1,32 @@
+#include "metal_fence.h"
+#include "core/devices/metal_output_devices.h"
+
+gnReturnCode gnCreateFenceFn(struct gnFence_t* fence, struct gnOutputDevice_t* device) {
+    fence->fence = malloc(sizeof(gnPlatformFence));
+
+    fence->fence->fence = [device->outputDevice->device newSharedEvent];
+    fence->fence->listener = [[MTLSharedEventListener alloc] init];
+    fence->fence->semaphore = dispatch_semaphore_create(1);
+
+    return GN_SUCCESS;
+}
+void gnSignalFenceFn(struct gnFence_t* fence) {
+    dispatch_semaphore_signal(fence->fence->semaphore);
+}
+void gnWaitForFenceFn(struct gnFence_t* fence, uint64_t timeout) {
+    dispatch_semaphore_wait(fence->fence->semaphore, timeout);
+}
+void gnResetFenceFn(struct gnFence_t* fence) {
+    dispatch_semaphore_signal(fence->fence->semaphore);
+    [fence->fence->fence setSignaledValue:0];
+    [fence->fence->fence notifyListener:fence->fence->listener
+        atValue:1
+        block:^(id<MTLSharedEvent> ev, uint64_t val) {
+        dispatch_semaphore_signal(fence->fence->semaphore);
+    }];
+}
+void gnDestroyFenceFn(struct gnFence_t* fence) {
+    [fence->fence->fence release];
+    [fence->fence->listener release];
+    free(fence->fence);
+}