Simple interface for some VM lifecycle hooks.

src/main/java/li/cil/oc2/api/bus/device/vm/VMLifecycleEventListener.java

@@ -0,0 +1,5 @@
+package li.cil.oc2.api.bus.device.vm;
+
+public interface VMLifecycleEventListener extends VMDevice {
+    void handleLifecycleEvent(VMLifecycleEventType event);
+}

src/main/java/li/cil/oc2/api/bus/device/vm/VMLifecycleEventType.java

@@ -0,0 +1,26 @@
+package li.cil.oc2.api.bus.device.vm;
+
+public enum VMLifecycleEventType {
+    /**
+     * Reported when the VM resumes running.
+     * <p>
+     * Fired after all devices reported success from {@link VMDevice#load(VMContext)}.
+     * <p>
+     * Fired on initial boot-up as well as when the VM resumes after being restored
+     * from a saved state. It is intended for awaiting asynchronous load operations.
+     */
+    RESUME_RUNNING,
+
+    /**
+     * Reported exactly once, when the VM first starts running.
+     * <p>
+     * Fired after all devices reported success from {@link VMDevice#load(VMContext)}.
+     * <p>
+     * If a running VM is restored from a saved state, this event will not be fired. It is
+     * intended for initializing the VM state on boot, e.g. by loading initial executable
+     * code into memory.
+     * <p>
+     * <em>This is invoked from the worker thread running the VM.</em>
+     */
+    INITIALIZE,
+}

src/main/java/li/cil/oc2/common/vm/VirtualMachineDeviceBusAdapter.java

@@ -4,13 +4,12 @@ import li.cil.ceres.api.Serialized;
 import li.cil.oc2.api.bus.device.Device;
 import li.cil.oc2.api.bus.device.vm.VMDevice;
 import li.cil.oc2.api.bus.device.vm.VMDeviceLoadResult;
+import li.cil.oc2.api.bus.device.vm.VMLifecycleEventListener;
+import li.cil.oc2.api.bus.device.vm.VMLifecycleEventType;
 import li.cil.sedna.api.Board;
 import li.cil.sedna.riscv.device.R5PlatformLevelInterruptController;
 
-import java.util.ArrayList;
-import java.util.BitSet;
-import java.util.HashMap;
-import java.util.Set;
+import java.util.*;
 
 public final class VirtualMachineDeviceBusAdapter {
     private final Board board;
@@ -19,6 +18,8 @@ public final class VirtualMachineDeviceBusAdapter {
     private final HashMap<VMDevice, ManagedVMContext> deviceContexts = new HashMap<>();
     private final ArrayList<VMDevice> incompleteLoads = new ArrayList<>();
 
+    private final HashSet<VMLifecycleEventListener> lifecycleEventListeners = new HashSet<>();
+
     ///////////////////////////////////////////////////////////////////
 
     // This is a superset of allocatedInterrupts. We use this so that after loading we
@@ -86,6 +87,12 @@ public final class VirtualMachineDeviceBusAdapter {
         incompleteLoads.addAll(deviceContexts.keySet());
     }
 
+    public void fireLifecycleEvent(final VMLifecycleEventType event) {
+        for (final VMLifecycleEventListener tickListener : lifecycleEventListeners) {
+            tickListener.handleLifecycleEvent(event);
+        }
+    }
+
     public void addDevices(final Set<Device> devices) {
         for (final Device device : devices) {
             if (device instanceof VMDevice) {
@@ -97,6 +104,10 @@ public final class VirtualMachineDeviceBusAdapter {
                 }
 
                 incompleteLoads.add(vmDevice);
+
+                if (vmDevice instanceof VMLifecycleEventListener) {
+                    lifecycleEventListeners.add((VMLifecycleEventListener) vmDevice);
+                }
             }
         }
     }
@@ -113,6 +124,10 @@ public final class VirtualMachineDeviceBusAdapter {
 
                 incompleteLoads.remove(vmDevice);
 
+                if (vmDevice instanceof VMLifecycleEventListener) {
+                    lifecycleEventListeners.remove(vmDevice);
+                }
+
                 vmDevice.unload();
             }
         }