<Codis><JedisPool><DeadLock>

Overview

Background: I start a thread [call thread A below]in Spark driver to handle opening files in codis, in which I start six thread [call sub threads below]to handle the files in parallel.
What happened:
- I found the codis openingFilePool never update since a given time.
- So I looked into the Thread Dump tools of spark, and saw that thread A is always been WAITING. As below:
- The normal one is as follow:
- See the difference?
  The thread should be TIMED_WAITING(sleep), not be WAITING(wait for some other threads to awake it)!
- It seems there is a deadlock?
Thread A get a jedis instance from JedisResourcePool to get all opening files.
Then, the sub threads handle these opening files and interact with codis in pipeline. [I use try(Pipeline pipeline = CodisPool.getPool().getResource().pipelined())]

Possible causes

I am not sure this is because 1) there is no enough instance in JedisPool; or 2) there is a deadlock?
- ```
try (Pipeline pipeline = CodisPool.getPool().getResource().pipelined())
```
  - I am not sure whether this code will close jedis and pipeline, or it will just close pipeline?
- JedisResourcePool is not thread-safe?
  - Some says that we should sync when we getResource() from JedisResourcePool. I am not sure.
  - And also I think should I configure the number of Jedis pool.

Final words

I have been wondering how to check whether the chained resource is closed. Uh... So I raised a question in stackoverflow.
Show the amzaing answer:

Try-with-resources close only variable, in your case Pipeline pipeline. You can read more in docs https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

You can check it with example:

MyResource class:

class MyResource implements AutoCloseable {

    public SubResource getSubResource() {
        return new SubResource();
    }

    @Override
    public void close() throws Exception {
        System.out.println("Resource closed");
    }
}

SubResource class:

class SubResource implements AutoCloseable{
    @Override
    public void close() throws Exception {
        System.out.println("SubResource closed");
    }
}

Main class:

class Main {

    public static void main(String[] args) {
        try (SubResource s = new MyResource().getSubResource()) {
            System.out.println("Before closing");
        } catch (Exception e) {
            e.printStackTrace();
        }

        System.out.println("After closing");
    }
}

Execution result:

Before closing
SubResource closed
After closing