Re: [Boost-users] [boost] [thread] thread handling question

Subject: Re: [Boost-users] [boost] [thread] thread handling question
From: Markus Pieper (onkelhotte_at_[hidden])
Date: 2016-06-09 13:04:05

Thanks, it worked!

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Am 2. Juni 2016 10:30:28 vorm. schrieb Andreas Wehrmann 
<a.wehrmann_at_[hidden]>:

> On 06/02/2016 10:07 AM, Markus Pieper wrote:
>> Hi, this may be a very dumb question… My boost version is 1.56.0.
>>
>> In my program I use a database logging technique. To avoid blocking
>> the main thread, I coded this:
>>
>> int main()
>> {
>>   while(bDoCalculations == true)
>> {
>>       // calculate some stuff
>>       m_Logger->doLogging();
>>    }
>> }
>>
>> void CLoggingData::doLogging() {
>>    std::vector<float>* Result;
>>    // fill Result
>> boost::thread (&CLoggingData::doStoreData, this, Result);
>> }
>>
>> void CLoggingData::doStoreData(std::vector<float>* dataVector) {
>>    // pass pointer to database writer instance
>>    delete dataVector;
>> }
>>
>> I do not use join() in the doLogging method because I don’t want the
>> main thread to block if the database is busy and will not respond
>> immediately.
>>
>> But then, after a long run I get a boost::thread_resource_error
>> exception. You may say: Of course, you never join your thread and
>> after a few thousands new threads you blow your stack.
>>
>> Well, but what can I do to get my desired behavior? In the
>> documentation I found this which I think of might help:
>>
>> You can use a thread_joiner to ensure that the thread has been joined
>> at the thread destructor.
>>
>> int main()
>> {
>>   boost::thread t(my_func);
>>    boost::thread_joiner g(t);
>>   // do someting else
>> } // here the thread_joiner destructor will join the thread before it
>> is destroyed.
>>
>> But where is the thread_joiner class implemented? Or do I have to add
>> something inside my doStoreData method to end the thread properly?
>>
>> Thanks in advance,
>> Markus
>>
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>>
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>
> Hey there,
>
> I had a similar problem. My main thread issues "tasks" which are to run
> asynchonously.
> The main thread may request many tasks to be executed.
> Once a task is finished, the result is reported back to the main thread,
> the proper task thread is joined and the next task will be started in a
> new thread.
>
> Initially I forgot to join the task threads which sooner or later
> (depending on how much was going on)
> lead to the exact same problem that you described
> (the OS keeps some info around when a thread ends; joining the thread
> will release the info).
>
> Here's basically what I did:
>
> 1. Keep a list of all ongoing/pending tasks
> 2. When a task is done, let it report back to main thread
> 3. When main thread receives such a "finished" message,
>      it looks through the list to find out what task is done and joins
> the proper thread instance.
>
> In my opinion you need to do something like the above anyway,
> because when the app is to shut down while tasks are still running you
> need to wait for them to "finish" anyway.
>
> Best regards,
> Andreas
>
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