promise-error.txt

Hi Jonathan,

I took an example from Data::Dump::Tree (DDT)and started playing with Promises, the 
goal was simply educative, I am following your "Parallelism, Concurrency,
and Asynchrony in Perl 6" document to try the different mechanisms. The final goal
being the parallelization of DDT as it is too sluggish and also in preparation of
Asciio 2.0. Tell me if you want the development branch and the example on github to
check the problems below.


Problem 1
=========

	for ^50
	{
	$dump_start = now ;
	my $d1 = start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ; 
	my $d2 = start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ; 
	my $d3 = start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ; 
	my $d4 = start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ; 
	my $d5 = start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ; 
	my $d6 = start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ; 
	my $d7 = start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ; 
	my $d8 = start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ; 

	await $d1, $d2, $d3, $d4, $d5, $d6, $d7, $d8 ;

	say "dump time: {now - $dump_start} s" ;
	}

The problem is that it first iterates quickly and then slows down considerably

dump time: 0.24248294 s # first iteration
dump time: 0.2493730 s
dump time: 0.2249258 s
dump time: 0.25128736 s
dump time: 0.24334974 s
dump time: 0.2577809 s
...
dump time: 0.4216805 s
dump time: 0.404167881 s
dump time: 0.40570028 s
dump time: 0.41778251 s
dump time: 0.4126616 s # last iteration 


I ran it with 500 iteration, around iteration 150 the time seems to stabilize just below 0.5s.
At iteration 500 it is half the time under 0.5s and half the time very slightly higher
with peaks around 0.7 s

Problem 2
=========

I changed the code to this loop and that call to ddt to show the promises, wrongly calling promises
threads in my example.

	for ^15
	{
	@threads.push: start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ;
	}

	ddt @threads ;

that worked fine and fast. I changed the code to

	for ^16 # change from ^15 to ^16
	{
	@threads.push: start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ;
	}

	ddt @threads ;


that doesn't work at all. The "ddt @threads" does not get executed, nothing get's schedules, no CPU is used. It's dead Jim.


Problem 3 
=========

I changed the code to

	for ^15 # change back to ^15
	{
	@threads.push: start $d.ddt: :get, { :$config, :$regex, :$match }, :title<config parsing>, :elements_filters[&sorter] ;
	}

	ddt @threads, :flat{1, 5} ; #changed the option to ddt


The option to ddt makes the rendering much slower, slow enough to that some promises get scheduled before the 
ddt call returns.

I ran it mucltiple times on the command line, sometimes it works, like the example below:

132 ~/4/P6-Data-Dump-Tree p6 time_threads.pl
time: 0.24393817 s
[15] @0
    0 = .Promise <Planned> 5 = .Promise <Kept>    10 = .Promise <Planned>
    1 = .Promise <Planned> 6 = .Promise <Planned> 11 = .Promise <Planned>
    2 = .Promise <Planned> 7 = .Promise <Planned> 12 = .Promise <Planned>
    3 = .Promise <Planned> 8 = .Promise <Planned> 13 = .Promise <Planned>
    4 = .Promise <Planned> 9 = .Promise <Planned> 14 = .Promise <Planned>

time: 0.5515428 s
total time 0.8070619 s


sometimes it fails with this error:
-----------------------------------

122 ~/4/P6-Data-Dump-Tree p6 time_threads.pl
time: 0.2489823 s
[15] @0
    0 = .Promise <Planned> 5 = .Promise <Planned> 10 = .Promise <Kept>
    1 = .Promise <Planned> 6 = .Promise <Planned> 11 = .Promise <Planned>
    2 = .Promise <Planned> 7 = .Promise <Kept>    12 = .Promise <Kept>
    3 = .Promise <Planned> 8 = .Promise <Planned> 13 = .Promise <Broken>
    4 = .Promise <Planned> 9 = .Promise <Planned> 14 = .Promise <Kept>

Tried to get the result of a broken Promise
  in block <unit> at time_threads.pl line 53

Original exception:
    Cannot find method 'specialize' on object of type NQPClassHOW
      in method reset at /home/nadim/nadim/devel/repositories/perl_modules/P6-Data-Dump-Tree/lib/Data/Dump/Tree.pm (Data::Dump::Tree) line 218

my code at line 218 looks like this :
	$.width //= %+((qx[stty size] || '0 80') ~~ /\d+ \s+ (\d+)/)[0] ;



Other times it fails like this without outputing the result of ddt: 
-------------------------------------------------------------------

122 ~/4/P6-Data-Dump-Tree p6 time_threads.pl
time: 0.24770038 s
Unhandled exception in code scheduled on thread 19
Unhandled exception in code scheduled on thread 18
Unhandled exception in code scheduled on thread 13
Unhandled exception in code scheduled on thread 6
Type check failed in binding to parameter 'value'; expected Any but got NQPMu (?)