CRaC & CRIU

1. Create a standard checkpoint/restore notification API
   • Use org.crac as a wrapper for:
     jdk.crac / javax.crac / -Dorg.crac.Core.Compat=..
2. Make the JDK "snapsafe":
   • i.e. act gracefully on checkpoint/restore & clone events
   • state, secrets, time, resources, ...
3. Integrate with checkpoint/restore mechanisms:
   • Currently only CRIU

• Serializes single processes to the file system

Using org.crac

•                   
  import org.crac.Context;
  import org.crac.Core;
  import org.crac.Resource;
  
  @Component
  public class MyCheckpointRestoreListener implements Resource {
  
    @Autowired
    public MyCheckpointRestoreListener(...) {
      Core.getGlobalContext().register(this);
      logger.info("=> MyCheckpointRestoreListener: Registering in {}", Core.getGlobalContext());
    }
    @Override
    public void beforeCheckpoint(Context<? extends Resource> context) {
      logger.info("=> MyCheckpointRestoreListener: beforeCheckpoint");
    }
    @Override
    public void afterRestore(Context<? extends Resource> context) {
      logger.info("=> MyCheckpointRestoreListener: afterRestore");
    }
  }
                    
                  

FireCRaCer DEMO

1. "Unattended" checkpoint/restore with unmodified JDK
    
2. Using a "CRaC"-enhanced JDK inside Firecracker
    
3. Using a "JVMTI-agent" implementing the org.crac API

Java-agent implementing org.crac

• Injected with -Dorg.crac.Core.Compat=io.simonis.crac

•                   
  package io.simonis.crac.impl;
  
  public class FirecrackerContext extends Context<Resource> {
  
    private final ArrayList<WeakReference<Resource>> resources = new ArrayList<>();
  
    @Override
    public void register(Resource resource) {
      resources.add(new WeakReference<Resource>(resource));
    }
  
    @Override
    public void beforeCheckpoint(Context<? extends Resource> context) throws CheckpointException {
      for (var iterator = resources.listIterator(resources.size()); iterator.hasPrevious();) {
        Resource r = iterator.previous().get();
        r.beforeCheckpoint(this);
        ...
    @Override
    public void afterRestore(Context<? extends Resource> context) throws RestoreException {
      for (var iterator = resources.listIterator(); iterator.hasNext();) {
        ...
                    
                  

JVMTI-agent controlling threads and GC

• Use JVMTI to suspend/resume threads before/after checkpointing:

•                   
  jint Java_io_simonis_SuspendResumeAgent_suspendThreads(JNIEnv *env, jclass cls) {
    jint threads_count;
    jthread *threads;
    jvmti->GetAllThreads(&threads_count, &threads);
    ...
    jvmtiError error = jvmti->SuspendThreadList(threads_count - 1, threads, errors);
  
  jint Java_io_simonis_SuspendResumeAgent_resumeThreads(JNIEnv *env, jclass cls) {
    jint threads_count;
    jthread *threads;
    jvmti->GetAllThreads(&threads_count, &threads);
    ...
    jvmtiError error = jvmti->ResumeThreadList(threads_count, threads, errors);
                    
                  

• Use JVMTI to perform a full GC before checkpointing:

•                   
  jint Java_io_simonis_SuspendResumeAgent_forceGC(JNIEnv *env, jclass cls) {
    jvmtiError error = jvmti->ForceGarbageCollection();