NAME

Coro::State - create and manage simple coroutines

SYNOPSIS

use Coro::State;

$new = new Coro::State sub {
   print "in coroutine (called with @_), switching back\n";
   $new->transfer ($main);
   print "in coroutine again, switching back\n";
   $new->transfer ($main);
}, 5;

$main = new Coro::State;

print "in main, switching to coroutine\n";
$main->transfer ($new);
print "back in main, switch to coroutine again\n";
$main->transfer ($new);
print "back in main\n";

DESCRIPTION

This module implements coroutines. Coroutines, similar to continuations, allow you to run more than one "thread of execution" in parallel. Unlike threads, there is no parallelism and only voluntary switching is used so locking problems are greatly reduced.

This can be used to implement non-local jumps, exception handling, continuations and more.

This module provides only low-level functionality. See Coro and related modules for a higher level process abstraction including scheduling.

MEMORY CONSUMPTION

A newly created coroutine that has not been used only allocates a relatively small (a few hundred bytes) structure. Only on the first transfer will perl stacks (a few k) and optionally C stack. All this is very system-dependent. On my x86_64-pc-linux-gnu system this amounts to about 8k per (non-trivial) coroutine.

FUNCTIONS

$coro = new Coro::State [$coderef[, @args...]]

Create a new coroutine and return it. The first transfer call to this coroutine will start execution at the given coderef. If the subroutine returns it will be executed again. If it throws an exception the program will terminate.

Calling exit in a coroutine will not work correctly, so do not do that.

If the coderef is omitted this function will create a new "empty" coroutine, i.e. a coroutine that cannot be transfered to but can be used to save the current coroutine in.

The returned object is an empty hash which can be used for any purpose whatsoever, for example when subclassing Coro::State.

$prev->transfer ($next, $flags)

Save the state of the current subroutine in $prev and switch to the coroutine saved in $next.

The "state" of a subroutine includes the scope, i.e. lexical variables and the current execution state (subroutine, stack). The $flags value can be used to specify that additional state to be saved (and later restored), by oring the following constants together:

Constant    Effect
SAVE_DEFAV  save/restore @_
SAVE_DEFSV  save/restore $_
SAVE_ERRSV  save/restore $@

These constants are not exported by default. If you don't need any extra additional state saved, use 0 as the flags value.

If you feel that something important is missing then tell me. Also remember that every function call that might call transfer (such as Coro::Channel::put) might clobber any global and/or special variables. Yes, this is by design ;) You can always create your own process abstraction model that saves these variables.

The easiest way to do this is to create your own scheduling primitive like this:

sub schedule {
   local ($_, $@, ...);
   $old->transfer ($new);
}

Coro::State::cctx_count

Returns the number of C-level coroutines allocated. If this number is very high (more than a dozen) it might help to identify points of C-level recursion in your code and moving this into a separate coroutine.

Coro::State::cctx_idle

Returns the number of allocated but idle (free for reuse) C level coroutines. As C level coroutines are curretly rarely being deallocated, a high number means that you used many C coroutines in the past.

BUGS

This module is not thread-safe. You must only ever use this module from the same thread (this requirement might be loosened in the future).

SEE ALSO

Coro.

AUTHOR

Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/