Coro
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change other per-coro global stuff such as C<$/> you I<must needs> revert
that change, which is most simply done by using local as in: C<< local $/
>>.
The idle pool size is limited to C<8> idle coros (this can be
adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
coros as required.
If you are concerned about pooled coros growing a lot because a
single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
{ terminate }> once per second or so to slowly replenish the pool. In
addition to that, when the stacks used by a handler grows larger than 32kb
(adjustable via $Coro::POOL_RSS) it will also be destroyed.
=cut
our $POOL_SIZE = 8;
our $POOL_RSS = 32 * 1024;
our @async_pool;
sub pool_handler {
while () {
eval {
&{&_pool_handler} while 1;
};
warn $@ if $@;
}
}
=back
=head1 STATIC METHODS
Static methods are actually functions that implicitly operate on the
current coro.
=over 4
=item schedule
Calls the scheduler. The scheduler will find the next coro that is
to be run from the ready queue and switches to it. The next coro
to be run is simply the one with the highest priority that is longest
in its ready queue. If there is no coro ready, it will call the
C<$Coro::idle> hook.
Please note that the current coro will I<not> be put into the ready
queue, so calling this function usually means you will never be called
again unless something else (e.g. an event handler) calls C<< ->ready >>,
thus waking you up.
This makes C<schedule> I<the> generic method to use to block the current
coro and wait for events: first you remember the current coro in
a variable, then arrange for some callback of yours to call C<< ->ready
>> on that once some event happens, and last you call C<schedule> to put
yourself to sleep. Note that a lot of things can wake your coro up,
so you need to check whether the event indeed happened, e.g. by storing the
status in a variable.
See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
=item cede
"Cede" to other coros. This function puts the current coro into
the ready queue and calls C<schedule>, which has the effect of giving
up the current "timeslice" to other coros of the same or higher
priority. Once your coro gets its turn again it will automatically be
resumed.
This function is often called C<yield> in other languages.
=item Coro::cede_notself
Works like cede, but is not exported by default and will cede to I<any>
coro, regardless of priority. This is useful sometimes to ensure
progress is made.
=item terminate [arg...]
Terminates the current coro with the given status values (see
L<cancel>). The values will not be copied, but referenced directly.
=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
These function install enter and leave winders in the current scope. The
enter block will be executed when on_enter is called and whenever the
current coro is re-entered by the scheduler, while the leave block is
executed whenever the current coro is blocked by the scheduler, and
also when the containing scope is exited (by whatever means, be it exit,
die, last etc.).
I<Neither invoking the scheduler, nor exceptions, are allowed within those
BLOCKs>. That means: do not even think about calling C<die> without an
eval, and do not even think of entering the scheduler in any way.
Since both BLOCKs are tied to the current scope, they will automatically
be removed when the current scope exits.
These functions implement the same concept as C<dynamic-wind> in scheme
does, and are useful when you want to localise some resource to a specific
coro.
They slow down thread switching considerably for coros that use them
(about 40% for a BLOCK with a single assignment, so thread switching is
still reasonably fast if the handlers are fast).
These functions are best understood by an example: The following function
will change the current timezone to "Antarctica/South_Pole", which
requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
which remember/change the current timezone and restore the previous
value, respectively, the timezone is only changed for the coro that
installed those handlers.
use POSIX qw(tzset);
async {
my $old_tz; # store outside TZ value here
Coro::on_enter {
$old_tz = $ENV{TZ}; # remember the old value
only way, and if you don't, then C<< ->cancel >> is always faster and more
direct.
=item $coro->schedule_to
Puts the current coro to sleep (like C<Coro::schedule>), but instead
of continuing with the next coro from the ready queue, always switch to
the given coro object (regardless of priority etc.). The readyness
state of that coro isn't changed.
This is an advanced method for special cases - I'd love to hear about any
uses for this one.
=item $coro->cede_to
Like C<schedule_to>, but puts the current coro into the ready
queue. This has the effect of temporarily switching to the given
coro, and continuing some time later.
This is an advanced method for special cases - I'd love to hear about any
uses for this one.
=item $coro->throw ([$scalar])
If C<$throw> is specified and defined, it will be thrown as an exception
inside the coro at the next convenient point in time. Otherwise
clears the exception object.
Coro will check for the exception each time a schedule-like-function
returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
>>, C<< Coro::Handle->readable >> and so on. Most of those functions (all
that are part of Coro itself) detect this case and return early in case an
exception is pending.
The exception object will be thrown "as is" with the specified scalar in
C<$@>, i.e. if it is a string, no line number or newline will be appended
(unlike with C<die>).
This can be used as a softer means than either C<cancel> or C<safe_cancel
>to ask a coro to end itself, although there is no guarantee that the
exception will lead to termination, and if the exception isn't caught it
might well end the whole program.
You might also think of C<throw> as being the moral equivalent of
C<kill>ing a coro with a signal (in this case, a scalar).
=item $coro->join
Wait until the coro terminates and return any values given to the
C<terminate> or C<cancel> functions. C<join> can be called concurrently
from multiple threads, and all will be resumed and given the status
return once the C<$coro> terminates.
=item $coro->on_destroy (\&cb)
Registers a callback that is called when this coro thread gets destroyed,
that is, after it's resources have been freed but before it is joined. The
callback gets passed the terminate/cancel arguments, if any, and I<must
not> die, under any circumstances.
There can be any number of C<on_destroy> callbacks per coro, and there is
currently no way to remove a callback once added.
=item $oldprio = $coro->prio ($newprio)
Sets (or gets, if the argument is missing) the priority of the
coro thread. Higher priority coro get run before lower priority
coros. Priorities are small signed integers (currently -4 .. +3),
that you can refer to using PRIO_xxx constants (use the import tag :prio
to get then):
PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
3 > 1 > 0 > -1 > -3 > -4
# set priority to HIGH
current->prio (PRIO_HIGH);
The idle coro thread ($Coro::idle) always has a lower priority than any
existing coro.
Changing the priority of the current coro will take effect immediately,
but changing the priority of a coro in the ready queue (but not running)
will only take effect after the next schedule (of that coro). This is a
bug that will be fixed in some future version.
=item $newprio = $coro->nice ($change)
Similar to C<prio>, but subtract the given value from the priority (i.e.
higher values mean lower priority, just as in UNIX's nice command).
=item $olddesc = $coro->desc ($newdesc)
Sets (or gets in case the argument is missing) the description for this
coro thread. This is just a free-form string you can associate with a
coro.
This method simply sets the C<< $coro->{desc} >> member to the given
string. You can modify this member directly if you wish, and in fact, this
is often preferred to indicate major processing states that can then be
seen for example in a L<Coro::Debug> session:
sub my_long_function {
local $Coro::current->{desc} = "now in my_long_function";
...
$Coro::current->{desc} = "my_long_function: phase 1";
...
$Coro::current->{desc} = "my_long_function: phase 2";
...
}
=cut
sub desc {
my $old = $_[0]{desc};
$_[0]{desc} = $_[1] if @_ > 1;
$old;
}
sub transfer {
require Carp;
Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
}
=back
=head1 GLOBAL FUNCTIONS
=over 4
=item Coro::nready
Returns the number of coro that are currently in the ready state,
i.e. that can be switched to by calling C<schedule> directory or
indirectly. The value C<0> means that the only runnable coro is the
currently running one, so C<cede> would have no effect, and C<schedule>
would cause a deadlock unless there is an idle handler that wakes up some
coro.
=item my $guard = Coro::guard { ... }
This function still exists, but is deprecated. Please use the
C<Guard::guard> function instead.
=cut
BEGIN { *guard = \&Guard::guard }
=item unblock_sub { ... }
This utility function takes a BLOCK or code reference and "unblocks" it,
returning a new coderef. Unblocking means that calling the new coderef
will return immediately without blocking, returning nothing, while the
original code ref will be called (with parameters) from within another
coro.
The reason this function exists is that many event libraries (such as
the venerable L<Event|Event> module) are not thread-safe (a weaker form
of reentrancy). This means you must not block within event callbacks,
otherwise you might suffer from crashes or worse. The only event library
currently known that is safe to use without C<unblock_sub> is L<EV> (but
you might still run into deadlocks if all event loops are blocked).
Coro will try to catch you when you block in the event loop
("FATAL: $Coro::idle blocked itself"), but this is just best effort and
only works when you do not run your own event loop.
This function allows your callbacks to block by executing them in another
coro where it is safe to block. One example where blocking is handy
is when you use the L<Coro::AIO|Coro::AIO> functions to save results to
disk, for example.
In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
creating event callbacks that want to block.
If your handler does not plan to block (e.g. simply sends a message to
another coro, or puts some other coro into the ready queue), there is
no reason to use C<unblock_sub>.
Note that you also need to use C<unblock_sub> for any other callbacks that
are indirectly executed by any C-based event loop. For example, when you
use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
provides callbacks that are the result of some event callback, then you
must not block either, or use C<unblock_sub>.
=cut
our @unblock_queue;
# we create a special coro because we want to cede,
# to reduce pressure on the coro pool (because most callbacks
# return immediately and can be reused) and because we cannot cede
# inside an event callback.
our $unblock_scheduler = new Coro sub {
while () {
while (my $cb = pop @unblock_queue) {
&async_pool (@$cb);
# for short-lived callbacks, this reduces pressure on the coro pool
# as the chance is very high that the async_poll coro will be back
# in the idle state when cede returns
cede;
}
schedule; # sleep well
}
};
$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
sub unblock_sub(&) {
my $cb = shift;
sub {
unshift @unblock_queue, [$cb, @_];
$unblock_scheduler->ready;
}
}
=item $cb = rouse_cb
Create and return a "rouse callback". That's a code reference that,
when called, will remember a copy of its arguments and notify the owner
coro of the callback.
See the next function.
=item @args = rouse_wait [$cb]
Wait for the specified rouse callback (or the last one that was created in
this coro).
As soon as the callback is invoked (or when the callback was invoked
before C<rouse_wait>), it will return the arguments originally passed to
the rouse callback. In scalar context, that means you get the I<last>
argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
statement at the end.
See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
=back
=cut
for my $module (qw(Channel RWLock Semaphore SemaphoreSet Signal Specific)) {
my $old = defined &{"Coro::$module\::new"} && \&{"Coro::$module\::new"};
*{"Coro::$module\::new"} = sub {
require "Coro/$module.pm";
# some modules have their new predefined in State.xs, some don't
*{"Coro::$module\::new"} = $old
if $old;
goto &{"Coro::$module\::new"};
};
}
1;
=head1 HOW TO WAIT FOR A CALLBACK
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