ThreadPoolExecutor and finalization

[Peter Levart]

Hi David,

On 10/31/17 08:45, David Holmes wrote:
>>> The docs for TPE cover this in detail: [1]
>>>
>>> Finalization
>>>     A pool that is no longer referenced in a program AND has no 
>>> remaining threads will be shutdown automatically. If you would like 
>>> to ensure that unreferenced pools are reclaimed even if users forget 
>>> to call shutdown(), then you must arrange that unused threads 
>>> eventually die, by setting appropriate keep-alive times, using a 
>>> lower bound of zero core threads and/or setting 
>>> allowCoreThreadTimeOut(boolean).
>>
>> I'm trying to understand the purpose of finalize() in TPE, but can't. 
>> I'm surely missing something. If the pool is no longer referenced AND 
>> there are no active threads, what is there left to shutdown() 
>> actually? All that remains is garbage that will eventually be GCed.
>
> Ummmmm .... I'm going to have to do some archaeology here ...
>
> David

I can imagine a thread pool where worker threads, while idling, don't 
have a reference to the pool so the pool can shutdown() itself when:

- the pool is no longer referenced AND
- there is no worker thread executing a task (i.e. all worker threads 
are idle)

In such state, the pool is not reachable and may be shutdown.

But it seems that TPE is not such a pool.

Regards, Peter

>
>> Regards, Peter
>>
>>>
>>> David
>>> -----
>>>
>>> [1] 
>>> https://docs.oracle.com/javase/9/docs/api/java/util/concurrent/ThreadPoolExecutor.html 
>>