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DATE 2016-12-01

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Key: archive_learn Value: 2016-12-01

Key: id Value: 543583

MESSAGE
DATE 2016-12-18
FROM ruben safir
SUBJECT Re: [Learn] Threads and Object Methods
From learn-bounces-at-nylxs.com Sun Dec 18 21:24:31 2016
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To: learn-at-nylxs.com
From: ruben safir
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Date: Sun, 18 Dec 2016 21:23:30 -0500
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On 12/18/2016 09:15 PM, ruben safir wrote:
> On 12/18/2016 04:40 PM, Vir Campestris wrote:
>> You're missing the second parameter to the function. Perhaps if he'd
>> written
>>
>> Reader foo;
>> std::thread paint(&reader::read_chunk, &foo);
>>
>> it would have made more sense to you. You can pass args to the function,
>> which may include a pointer to an object of the type. I prefer to pass a
>> pointer to a static member function for the first parameter which takes
>> a pointer to an object of the class and invokes a corresponding
>> non-static member.
>>
>> Andy
>
>
> Not really. There are data members of the object that are dynamically altered
> and stored in the private encapsulation of the object which a a method handles
> inside the thread. read_chunk is a member of the Image class and it is
> assigned indexes within a block of memory, and a chunk of raw data. It
> interprets the block of memory and writes to the block of memory which is
> private to an instance of Image. The idea was to create a number of threads
> that write to the block, each in its assigned area, simultaneously in parallel.
>
> read_chunk looks like this
>
> void Image::read_chunk ( )
> {
> CHUNKY * new_chunk = set_chunk();//the chunk construction call is within
> std::cout << "Type " << new_chunk->type() << std::endl;
> std::cout << "Length " << new_chunk->length() << std::endl;
> std::cout << "CRC " << new_chunk->cr() << std::endl;
>
> if(new_chunk->type() == "IHDR")
> {
> std::cout << "we have a header chunk " << std::endl;
> IHDR * head = new IHDR;
> unsigned char * cur = new_chunk->data(); //NOTE:: cur is now point at the new heap for in CHNUNK and not the index for the file
> head->width = ntohl( *(reinterpret_cast(cur ) ) );
> cur += 4;
> head->height = ntohl( *(reinterpret_cast( cur ) ) );
> cur += 4;
> head->depth = *( reinterpret_cast( cur ) );
> cur++;
> head->color_type = *( reinterpret_cast( cur ) );
> cur++;
> head->compress = *( reinterpret_cast( cur ) );
> cur++;
> head->filter = *( reinterpret_cast( cur ) );
> cur++;
> head->interlace = *( reinterpret_cast( cur ) );
> cur++;
>
> canvas_size = static_cast(head->height) * static_cast(head->width) * blank_canvas_psize(*head);
> canvas = new unsigned char[ canvas_size ];
> std::cout << "Canvas made: " << static_cast(head->height) * static_cast(head->width) * blank_canvas_psize(*head) << " bytes" << std::endl;
> //char tmp;
> //std::cin >> tmp;
> }
>
> if(new_chunk->type() == "IDAT")
> {
> //confusion here. Do we want to create a new data array on the heap to pass through to the images for placement on canvas?
> //No. Not needed. Use the CHUNKY object instead. It already has the data array. Have the chunky obj schedule itself for
> //copy to the canvas
> set_canvas(*new_chunk); //SET MUTEX LOCK and assign canvas index to a CHUNKY object
> }
>
> if(new_chunk->type() == "IEND")
> {
> std::cout << "we have a IEND chunk " << std::endl;
> //set_index(get_index() + 12 + new_chunk->length() ) ;
> return;
> }
> std::thread ctch = getNext(); //calls this method in recursion
> ctch.join(); //I want this to be detached
> //read_chunk();
> return ;
> } /* ----- end of method Image::read_chunk ----- */
>
>


and I had to use a lamda for the thread

std::thread Image::getNext ()
{
std::cout << std::endl << "getNext" << std::endl;
// next_index();
std::thread paint( [this]{ read_chunk(); } );
std::cout << std::endl << "**created thread**" << paint.get_id() << std::endl;
return paint;
} /* ----- end of method Image::getNext ----- */


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