RandomData | Random data generator

Typescript is not able to check for null data across components because type checking would have to be done at runtime instead of compile time. The safest way to implement this would be to pass person in as a prop.

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Here is how I solved it: Not the best solution, but works.

There are indeed some issues with your code:

The result of fetch() will be either:

• an empty list if items is empty
• the result of recursively applying fetch(randomData(item)) on each item in the items list Since there is no recursion leaf that returns a non-empty list, and parent calls don’t add anything to the list either, it can only return an empty result.

Maybe you wanted to include the randomData() in the result as well?

You are using Executors.newFixedThreadPool(4). As the name indicates, the number of threads will be fixed, so when all threads are exhausted, new tasks are queued.

The problem is that you are using join() to wait for some of those new tasks. So on one hand you are blocking one of the threads, and on the other hand you are waiting for something you just put on the queue.

As it is recursive, if it reaches a depth of 4, it will deadlock.

The simplest way to prevent this would be to use a ForkJoinPool. This kind of pool will spawn new threads when one of its threads gets blocked.

As a side note, a ForkJoinPool uses daemon threads, so they don’t prevent the JVM from terminating. If you want to use a Fixed Thread Pool, you have to call shutdown() on it to make sure it allows termination – or configure it to use daemon threads.

Your code is building a lot of intermediate collections and blocking on a lot of join() calls. CompletableFuture is designed to chain related stages of computation thanks to its implementation of CompletionStage, and not just merely using it as a Future that can be completed.

Without changing your current logic, first you could make fetch() return a Stream, which removes a lot of collect()/stream() calls:

If I remember correctly using new in field initialization is forbidden in Java Card. You either have to perform the new from within the static install method (or a method called from install) or you can mark the field private, in which case the array is stored in the constant pool. I would strongly recommend the latter. Basically, no static code execution is allowed.

Using TRUE and FALSE as public static fields is not a good idea either, as they would be reference lookups, which is vulnerable to timing oracles. The whole idea of having TRUE and FALSE defined this way is to protect against such oracles as well as fault injection; I suggest to make them private.

You are calling method for API call in mounted and generating the random list from the most played list in created. But as per the lifecycle diagram of vue given here, you can see that created hook comes first and then mounted hook. So that way you are creating random list on an empty most played array.

As a solution call the getMostPlayed method inside created and randomItem method inside getMostPlayed after API response.

Something like this :

There's nothing wrong with your example, it works.

Please note that the expireAfterSeconds you specify is the duration after createdAt when the document expires, and that instant is the earliest time at which the document may be deleted, but there is no guarantee that the deletion will happen "immediately", exactly at that time.

Quoting from MongoDB docs: TTL indexes: Timing of the Delete Operation:

The TTL index does not guarantee that expired data will be deleted immediately upon expiration. There may be a delay between the time a document expires and the time that MongoDB removes the document from the database.

The background task that removes expired documents runs every 60 seconds. As a result, documents may remain in a collection during the period between the expiration of the document and the running of the background task.

Because the duration of the removal operation depends on the workload of your mongod instance, expired data may exist for some time beyond the 60 second period between runs of the background task.

As you can see, if a document expires, at worst case it may take 60 seconds for the background task to kick in and start removing expired documents, and if there are many (or the database is under heavy load), it may take some time to delete all expired documents.

Solution was to use the following combination

Your problem with the duplicate output is because you are assigning the data to randomData initially. React then rerenders (yielding the first console output) and only then calls your useEffect hook.

I would propose you don't use useEffect at all but instead an initialization function for useState:

You are very close. Your problem is here: