• Dr.No (65/65) May 31 2018 My application create some HTML which is then converted to PDF by
• Paul Backus (6/9) May 31 2018 It looks like wkhtmltopdf does not support multithreaded use; see
• Dr.No (10/19) Jun 01 2018 Can I run that function in another memory space within my

Dr.No <jckj33 gmail.com> writes:

My application create some HTML which is then converted to PDF by 
wkhtmltopdf library. I'm trying to figure out how make the PDF 
generation run parallel, currently, it's running linearly. My 
guess is wkhtmltopdf internal variables is preventing 
parallelization. But I'm new to parallization and I don't know 
how to solve that by now. I guesses that that function from an 
external thread would make each wkhtmltopdf initilization run on 
its memory space, similiar to a process. But since it is not 
working, I guess this isn't how it's working.
I'm not asking to just give me the code ready (if it's somehow 
complex) brather some directions, how I may archive that.


Here's my current code:

void genPDFImplt(string htmlFilename, string outputpdfFilename)
{
	import pdf;
	import std.string : toStringz;

	/* Init wkhtmltopdf in graphics less mode */
	wkhtmltopdf_init(0);
	wkhtmltopdf_global_settings *gs = 
wkhtmltopdf_create_global_settings();
	/* We want the result to be storred in the file called test.pdf 
*/
	wkhtmltopdf_set_global_setting(gs, "out", 
outputpdfFilename.toStringz);
	wkhtmltopdf_object_settings *os = 
wkhtmltopdf_create_object_settings();
	/* We want to convert to convert the qstring documentation page 
*/
	wkhtmltopdf_set_object_setting(os, "page", 
htmlFilename.toStringz);
	/* Create the actual converter object used to convert the pages 
*/
	wkhtmltopdf_converter * c = wkhtmltopdf_create_converter(gs);
	static if(0) {
		/* Call the progress_changed function when progress changes */
		wkhtmltopdf_set_progress_changed_callback(c, 
&pdf_progress_changed);
		/* Call the phase _changed function when the phase changes */
		wkhtmltopdf_set_phase_changed_callback(c, &pdf_phase_changed);
		/* Call the error function when an error occures */
		wkhtmltopdf_set_error_callback(c, &pdf_error);
		/* Call the waring function when a warning is issued */
		wkhtmltopdf_set_warning_callback(c, &pdf_warning);
	}
	scope(exit) {
		/* Destroy the converter object since we are done with it */
		wkhtmltopdf_destroy_converter(c);
		/* We will no longer be needing wkhtmltopdf funcionality */
		wkhtmltopdf_deinit();
	}
	wkhtmltopdf_add_object(c, os, null);
	/* Perform the actual convertion */
	wkhtmltopdf_convert(c);
}


called from a loop like this:

foreach(string file; parallel(files)) {
    auto res = doSomething(file);
    auto htmlfile = genHtmlFile(res);
    auto pdffile = genTmpPDFFilename();
    genPDFImplt(htmlfiel, pdffile);
}



Running in a dual core CPU, with 4 threads. It's genrating
one PDF per iteration rather 4. I've made sure already it's the 
genPDFImplt() which is doing that.
	

Paul Backus <snarwin gmail.com> writes:

On Thursday, 31 May 2018 at 19:26:12 UTC, Dr.No wrote:
 My application create some HTML which is then converted to PDF 
 by wkhtmltopdf library. I'm trying to figure out how make the 
 PDF generation run parallel, currently, it's running linearly.

It looks like wkhtmltopdf does not support multithreaded use; see 
here:

https://github.com/wkhtmltopdf/wkhtmltopdf/issues/1711

So, if you want to run the conversions in parallel, you will have 
to use separate processes.

Dr.No <jckj33 gmail.com> writes:

On Friday, 1 June 2018 at 02:30:34 UTC, Paul Backus wrote:
 On Thursday, 31 May 2018 at 19:26:12 UTC, Dr.No wrote:
 My application create some HTML which is then converted to PDF 
 by wkhtmltopdf library. I'm trying to figure out how make the 
 PDF generation run parallel, currently, it's running linearly.

 It looks like wkhtmltopdf does not support multithreaded use; 
 see here:

 https://github.com/wkhtmltopdf/wkhtmltopdf/issues/1711

 So, if you want to run the conversions in parallel, you will 
 have to use separate processes.

Can I run that function in another memory space within my 
application, making even __gshared be allocated in that memory 
space, so that it seems it is another process? it's quite similar 
to thread but everything is allocated in that new memory space 
including __gshared.
I started calling the wkhtmltopdf executable by I wanted to see 
if there's a signficative gain in performance calling the library 
directly. My application do generate a lot of PDFs so I'd like to 
optimiza as possible.