Error:

I would like to understand in what scenario the following example would cause a null pointer exception.

For example:

1）

public class DataLoaderAsync {
    private volatile Future task = null;
    private ReentrantLock reentrantLock = new ReentrantLock();
    public void start(Runnable runnable) {
        if (this.task == null) {
            try {
                reentrantLock.lock();

                if (this.task == null) {
                    this.task = ExecutorServiceMgr.getCatWrappedExecutorService().submit(runnable);
                }
            } finally {
                reentrantLock.unlock();
            }
        }
    }
    public void waitForCompletion() {
        Future currentTask = this.task;
        if (currentTask == null) {
            throw new DataLoaderRuntimeException("The task is not initialized yet");
        }
        if (currentTask.isDone()) {
            return;
        }
        try {
            reentrantLock.lock();
            if (currentTask.isDone()) {
                return;
            }
            FutureUtil.getOrCatch(currentTask);
        } finally {
            ***reentrantLock.unlock();*** // null position
        }
    }
}


waitForPolicyLoader java.lang.NullPointerException: Cannot invoke "java.util.concurrent.locks.ReentrantLock.unlock()" because "this.reentrantLock" is null
    at xxxx.DataLoaderAsync.waitForCompletion(DataLoaderAsync.java:58)
    at xxxx.DataBusiness.waitForLoader(DirectPolicyDataBusiness.java:97)
    at xxxx.DataBusiness.loadPolicies(ShareSpecialPolicyDataBusiness.java:204)
    at com.dianping.cat.async.CatWrappedRunnable.run(CatWrappedRunnable.java:29)
    at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
    at com.google.common.util.concurrent.TrustedListenableFutureTask$TrustedFutureInterruptibleTask.runInterruptibly(TrustedListenableFutureTask.java:131)
    at com.google.common.util.concurrent.InterruptibleTask.run(InterruptibleTask.java:74)
    at com.google.common.util.concurrent.TrustedListenableFutureTask.run(TrustedListenableFutureTask.java:82)
    at java.base/java.util.concurrent.ThreadPerTaskExecutor$TaskRunner.run(ThreadPerTaskExecutor.java:314)
    at java.base/java.lang.VirtualThread.run(VirtualThread.java:309)

2）

 public static Set<SubKey> getOrLoadPolicies(Context searchContext) {
    try {
        Set<SubKey> policies = searchContext.getReadonlyInfo().getPolicies();
        if (policies != null) {
            return policies;
        }
        Set<SubKey> avRedis = READER.getPolicies(searchContext);
        searchContext.getReadonlyInfo().setPolicies(avRedis); // null position
        return avRedis;
    } catch (Exception e) {
        LogManager.build(LOG_LOCATION, "getPolicies", e).error();
    }
    return Sets.newHashSet();
}


getPolicies java.lang.NullPointerException: Cannot invoke "xxx.setPolicies(java.util.Set)" because the return value of "xxx.Context.getReadonlyInfo()" is null
at xxx.getOrLoadPolicies(Forbidden.java:183)
at xxx.init(AbstractPolicyFilter.java:173)
at xxx.<init>(AbstractPolicyFilter.java:111)
at com.dianping.cat.async.CatWrappedRunnable.lambda$run$0(CatWrappedRunnable.java:30)
at com.dianping.cat.async.CatAsyncSupportTemplate.doExecute(CatAsyncSupportTemplate.java:121)
at com.dianping.cat.async.CatAsyncSupportTemplate.execute(CatAsyncSupportTemplate.java:96)
at com.dianping.cat.async.CatWrappedRunnable.run(CatWrappedRunnable.java:29)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
at com.google.common.util.concurrent.TrustedListenableFutureTask$TrustedFutureInterruptibleTask.runInterruptibly(TrustedListenableFutureTask.java:131)
at com.google.common.util.concurrent.InterruptibleTask.run(InterruptibleTask.java:74)
at com.google.common.util.concurrent.TrustedListenableFutureTask.run(TrustedListenableFutureTask.java:82)
at java.base/java.util.concurrent.ThreadPerTaskExecutor$TaskRunner.run(ThreadPerTaskExecutor.java:314)
at java.base/java.lang.VirtualThread.run(VirtualThread.java:309)

java version:
openjdk version “21.0.3” 2024-04-16 LTS
OpenJDK Runtime Environment Temurin-21.0.3+9 (build 21.0.3+9-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.3+9 (build 21.0.3+9-LTS, mixed mode, sharing)

Know what scenarios will trigger it.