I used the same code posted above only changing syntax needed to create Coro and OS threads.
This is not working code but the only difference is my actual code has functions that connect to vendor api.

#!/usr/bin/perl
$|=1;
print "Start time ".(localtime). "\n";
use strict;
use threads;
use CGI qw(:standard);
use XML::Simple;
use JSON qw(encode_json);
use MIME::Base64 qw(encode_base64);
use DBI;
use SOAP::Lite;
use POSIX qw(ceil);
use Data::Dumper;
use CHI;
$XML::Simple::PREFERRED_PARSER='XML::Parser';
$SOAP::Constants::DO_NOT_USE_CHARSET = 1;

my (@req,@odata,@errdet)=();
    my %threads=();
    foreach my $vnd (@req){
        #$threads{$vnd}=threads->create({ 'context' => 'list', 'exit' 
+=> 'thread_only' },\&startthread,$vnd,$SCH);
        $threads{$vnd}=async{&startthread($vnd,$SCH) };
    }
    cede;
    foreach my $vnd (keys %threads) 
    {
        my($err,$data) =$threads{$vnd}->join();
        if ($err eq 'N') {
            push @odata,@{$data};
        }
        }elseif($err eq 'Y'){
            push @errdet,$data;
        }elsif($threads{$vnd}->error) # with threads it was useful,
        {
            push @errdet,{ Vnd=>$vnd, ErrorCode=>26,ErrorMsg=>$threads
+{$vnd}->error};
        }
     }    


sub startthread
{
    my ($vendor,$SCH)=@_;
    my($err,$data) =();
    require './'.$vendor.'functions.pl"; #load vendor specific code
    ($err,$data)=&getvendordata($SCH);
    return($err,$data);
}

#vendor functions has somewhat code like this besides functions specif
+ic to each vendor api
#fetch data serially in a loop waiting for each call to finish before 
+going on next
sub getvendordata
{
    my $SCH=shift;
    #perform vendor specific tasks mostly SOAP::Lite calls to api
    #Has to perform multiple calls some of them depend on output of pr
+evious calls
    #Also have to make simultaneous calls which may not be related to 
+each other can be done parallelly.
    #e.g. first call to api returns a list of products subsequent call
+s to fetch details.
    #If i start threads/forks again here most of the time program cras
+hes :(
    my ($err,@data)=();
    my @products=getproduects();
        #Maybe i can start coro routines here to get all listed detail
+s simultaneously
    foreach my $product (@products)
    {
        #fetch product details over api
        push @data,$product->getdetails;
    }
    return ($err,\@data);
}
[download]

Coro Code

use strict;
use Coro;
#use Coro::LWP;
use LWP::Protocol::AnyEvent::http;
use CGI qw(:standard);
use XML::Simple;
use JSON qw(encode_json);
use MIME::Base64 qw(encode_base64);
use DBI;
use POSIX qw(ceil);
use Data::Dumper;
use CHI;
use SOAP::Lite;
use SOAP::Transport::HTTP; 
$XML::Simple::PREFERRED_PARSER='XML::Parser';
$SOAP::Constants::DO_NOT_USE_CHARSET = 1;

my (@req,@odata,@errdet)=();
    my %threads=();
    foreach my $vnd (@req){
        #$threads{$vnd}=threads->create({ 'context' => 'list', 'exit' 
+=> 'thread_only' },\&startthread,$vnd,$SCH);
        $threads{$vnd}=async{&startthread($vnd,$SCH) };
    }
    cede;
    foreach my $vnd (keys %threads) 
    {
        my($err,$data) =$threads{$vnd}->join();
        if ($err eq 'N') {
            push @odata,@{$data};
        }
        }elseif($err eq 'Y'){
            push @errdet,$data;
        }elsif($threads{$vnd}->error) # with threads it was useful,
        {
            push @errdet,{ Vnd=>$vnd, ErrorCode=>26,ErrorMsg=>$threads
+{$vnd}->error};
        }
     }    


sub startthread
{
    my ($vendor,$SCH)=@_;
    my($err,$data) =();
    require './'.$vendor.'functions.pl"; #load vendor specific code
    ($err,$data)=&getvendordata($SCH);
    return($err,$data);
}

#vendor functions has somewhat code like this besides functions specif
+ic to each vendor api
#fetch data asyncronously with coro async for each product
sub getvendordata
{
    my $SCH=shift;
    #perform vendor specific tasks mostly SOAP::Lite calls to api
    #Has to perform multiple calls some of them depend on output of pr
+evious calls
    #Also have to make simultaneous calls which may not be related to 
+each other can be done parallelly.
    #e.g. first call to api returns a list of products subsequent call
+s to fetch details.
    #If i start threads/forks again here most of the time program cras
+hes :(
    my ($err,@data)=();
    my @products=getproduects();
        #Maybe i can start coro routines here to get all listed detail
+s simultaneously
    my @tasks=();
    foreach my $product (@products)
    {
        #fetch product details over api
        push @tasks,async {push @data,$product->getdetails};
    }
    foreach my $task (@ftasks) {        $task->join();    }
    return ($err,\@data);
}
[download]

I wait for all threads to finish by joining them.