Make VM lifecycle events allow being used to sync up device state pre/post resume.

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

@@ -1,6 +1,29 @@
 package li.cil.oc2.api.bus.device.vm;
 
 public enum VMDeviceLifecycleEventType {
+    /**
+     * Fired 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>
+     */
+    INITIALIZING,
+
+    /**
+     * Fired when the VM is paused, typically before state is persisted.
+     * <p>
+     * Allows devices that offer interaction to external code-flow to suspend
+     * such interactions until {@link #RESUMED_RUNNING} is fired. This is required
+     * if such interactions may modify VM state, to prevent corrupting data being
+     * serialized asynchronously.
+     */
+    PAUSING,
+
     /**
      * Fired when the VM resumes running.
      * <p>
@@ -13,17 +36,16 @@ public enum VMDeviceLifecycleEventType {
     RESUME_RUNNING,
 
     /**
-     * Fired exactly once, when the VM first starts running.
+     * Fired when the VM resumed running.
      * <p>
-     * Fired after all devices reported success from {@link VMDevice#load(VMContext)}.
+     * Fired after {@link #RESUME_RUNNING} has been fired and handled by all devices.
      * <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.
+     * Allows device initialization that relies on all other devices having fully loaded.
      * <p>
-     * <em>This is invoked from the worker thread running the VM.</em>
+     * Typically this is used in combination with {@link #PAUSING}, to re-enable external
+     * interactions after VM state is guaranteed to be safe to modify again.
      */
-    INITIALIZE,
+    RESUMED_RUNNING,
 
     /**
      * Fired when the device is disposed, either because the VM is disposed or the source

src/main/java/li/cil/oc2/common/bus/device/item/ByteBufferFlashMemoryVMDevice.java

@@ -64,7 +64,7 @@ public final class ByteBufferFlashMemoryVMDevice extends IdentityProxy<ItemStack
     @Override
     public void handleLifecycleEvent(final VMDeviceLifecycleEventType event) {
         switch (event) {
-            case INITIALIZE:
+            case INITIALIZING:
                 // TODO Have start address passed with event?
                 copyDataToMemory(0x80000000L);
                 break;

src/main/java/li/cil/oc2/common/bus/device/item/FirmwareFlashMemoryVMDevice.java

@@ -30,7 +30,7 @@ public final class FirmwareFlashMemoryVMDevice extends IdentityProxy<ItemStack>
     @Override
     public void handleLifecycleEvent(final VMDeviceLifecycleEventType event) {
         switch (event) {
-            case INITIALIZE:
+            case INITIALIZING:
                 // TODO Have start address passed with event?
                 firmware.run(memoryMap, 0x80000000L);
                 break;

src/main/java/li/cil/oc2/common/tileentity/ComputerTileEntity.java

@@ -407,18 +407,19 @@ public final class ComputerTileEntity extends AbstractTileEntity implements ITic
 
         joinVirtualMachine();
 
-        tag.put(TERMINAL_TAG_NAME, NBTSerialization.serialize(terminal));
-
-        tag.put(BUS_ELEMENT_TAG_NAME, NBTSerialization.serialize(busElement));
-        tag.put(VIRTUAL_MACHINE_TAG_NAME, NBTSerialization.serialize(virtualMachine));
-
         if (runner != null) {
             tag.put(RUNNER_TAG_NAME, NBTSerialization.serialize(runner));
+            virtualMachine.vmAdapter.fireLifecycleEvent(VMDeviceLifecycleEventType.PAUSING);
             runner.scheduleResumeEvent(); // Allow synchronizing to async device saves.
         } else {
             NBTUtils.putEnum(tag, RUN_STATE_TAG_NAME, runState);
         }
 
+        tag.put(TERMINAL_TAG_NAME, NBTSerialization.serialize(terminal));
+
+        tag.put(BUS_ELEMENT_TAG_NAME, NBTSerialization.serialize(busElement));
+        tag.put(VIRTUAL_MACHINE_TAG_NAME, NBTSerialization.serialize(virtualMachine));
+
         final CompoundNBT items = new CompoundNBT();
         items.put(MEMORY_TAG_NAME, memoryItemHandler.serializeNBT());
         items.put(HARD_DRIVE_TAG_NAME, hardDriveItemHandler.serializeNBT());
@@ -739,12 +740,13 @@ public final class ComputerTileEntity extends AbstractTileEntity implements ITic
         protected void handleBeforeRun() {
             if (!firedInitializationEvent) {
                 firedInitializationEvent = true;
-                virtualMachine.vmAdapter.fireLifecycleEvent(VMDeviceLifecycleEventType.INITIALIZE);
+                virtualMachine.vmAdapter.fireLifecycleEvent(VMDeviceLifecycleEventType.INITIALIZING);
             }
 
             if (!firedResumeEvent) {
                 firedResumeEvent = true;
                 virtualMachine.vmAdapter.fireLifecycleEvent(VMDeviceLifecycleEventType.RESUME_RUNNING);
+                virtualMachine.vmAdapter.fireLifecycleEvent(VMDeviceLifecycleEventType.RESUMED_RUNNING);
             }
 
             int value;