This document discusses the Coro module in Perl, which provides coroutines (lightweight threads) functionality. Coroutines allow multiple operations to run concurrently within a single thread by swapping between them. The Coro module implements coroutines using continuations. Examples shown include using coroutines with timers, semaphores, and sockets. Coroutines can be integrated with the AnyEvent library to provide asynchronous functionality.

1. Cooperative Threads

2.  “First class continuations called Coroutines”
 A pseudo-threads suite implemented on Perl
 Only one thread is running in any moment
Why do we need it?
 Because “real” threads are difficult
 And “real” Perl threads are not threads at all –
almost processes
 Integration with AnyEvent

3. Won’t print anything
The main program ends without giving the
coroutine chance to run
Need to add a “cede;” in the end
use Coro;
async {
print "hellon";
};

4. use Coro;
async {
print "async 1n";
cede;
print "async 2n";
};
print "main 1n";
cede;
print "main 2n";
cede;
Will Print:
main 1
async 1
main 2
async 2

5.  If the test inside the async block fails, we will get the following
messge:
• FATAL: deadlock detected at - line 0
 Main program gave up the CPU, and is not in ready mode
 Async block ended already
 No runnable code – oops.
 What if we want to wait for something to happen? (AnyEvent –
Later)
use Coro;
my $wakeme = $Coro::current;
async {
$wakeme->ready if 0.5 < rand;
};
schedule;

6.  Can be upped and downed
multiple times
 Can be used with guard:
my $guard = $lock->guard;
use Coro;
use Coro::Semaphore;
my $sem = new Coro::Semaphore
0; # a locked semaphore
async {
print "unlocking semaphoren";
$sem->up;
};
print "trying to lock semaphoren";
$sem->down;
print "we got it!n";

7. use Coro;
use Coro::Semaphore;
my $calculate = new Coro::Channel;
my $result = new Coro::Channel;
async {
while (1) {
my $num = $calculate->get; # read a number
$num **= 2; # square it
$result->put ($num); # put the result into the result queue
}
};

8. use Coro;
use Coro::Socket;
sub finger {
my ($user, $host) = @_;
my $fh = new Coro::Socket PeerHost => $host, PeerPort => "finger"
or die "$user@$host: $!";
print $fh "$usern";
print "$user@$host: $_" while <$fh>;
print "$user@$host: donen";
}
# now finger a few accounts
for (
(async { finger "abc", "cornell.edu" }),
(async { finger "sebbo", "world.std.com" }),
(async { finger "trouble", "noc.dfn.de" }) ) {
$_->join; # wait for the result
}

9. use Coro::Timer;
async {
say "before sleep 10";
Coro::Timer::sleep(10);
say "after sleep 10";
};
 Internally, uses AnyEvent

10. For using AnyEvent, you need event loop
• Can put it in the main thread, or in async block
When both Coro and AnyEvent are loaded,
Coro::AnyEvent is automatically loaded

11. use Modern::Perl;
use Coro;
use AnyEvent;
use AnyEvent::Impl::Perl;
use Coro::Timer;
$|=1;
for my $t (10, 20) {
async {
say "before sleep $t";
Coro::Timer::sleep($t);
say "after sleep $t";
};
}
my $t1 = AE::timer 5, 0, sub {say "it's time 5"};
my $t2 = AE::timer 15, 0, sub {say "it's time 15"};
say "before loop";
AnyEvent->condvar->recv;
The Output:
before loop
before sleep 10
before sleep 20
it's time 5
after sleep 10
it's time 15
after sleep 20