Re: [boost] [thread] TSS cleanup

Subject: Re: [boost] [thread] TSS cleanup
From: Anthony Williams (anthony.ajw_at_[hidden])
Date: 2008-09-26 16:43:11

"Felipe Magno de Almeida" <felipe.m.almeida_at_[hidden]> writes:

> On Mon, Sep 22, 2008 at 1:05 PM, Anthony Williams <anthony.ajw_at_[hidden]> wrote:
>> "Felipe Magno de Almeida" <felipe.m.almeida_at_[hidden]> writes:
>>
>>> I would like to know if the storage created for
>>> boost::thread_specific_ptr in the tss
>>> specific code for win32 is free'd after the destruction of said
>>> boost::thread_specific_ptr, or
>>> if it stays until the end of the process.
>>
>> Storage is allocated on a per-thread basis, and freed when the thread exits.
>>
>>> For example:
>>>
>>> for(int i = very_big_number;i--;i > 0)
>>>   boost::thread_specific_ptr<int> p(new int);
>>>
>>> To my knowledge, the pointer returned by new in this case is freed.
>>> But does the int* that is created to store the pointer to new int is also
>>> freed, or this program will get only bigger and bigger?
>>
>> As written this code is fine: it will reuse the same slot since p will
>> have the same address each time through, and it uses the address as
>> the key. It is undefined behaviour if other threads can still try and
>> access a given thread_specific_ptr (including having data stored
>> associated with it) after it has been destroyed.
>
> Well, so for spirit it would indeed get only bigger. Since it will hardly
> reuse slots.
> I see the tss algorithm is linear as well.
>
>> If you create and destroy thread_specific_ptr instances all over the
>> place then in general this will increase the list for each thread that
>> accesses the tsp. It shouldn't be too hard to have the TSS entry be
>> removed from the list when it is no longer needed. I'll try and get
>> round to sorting it for Boost 1.37. If you raise a trac ticket I'll be
>> more likely to remember.
>
> Would this work? It seems to fix my problem:

It looks like it at first glance.

Anthony
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