NAME

       "IO::Async::Function" - call a function asynchronously

SYNOPSIS

        use IO::Async::Function;

        use IO::Async::Loop;
        my $loop = IO::Async::Loop->new;

        my $function = IO::Async::Function->new(
           code => sub {
              my ( $number ) = @_;
              return is_prime( $number );
           },
        );

        $loop->add( $function );

        $function->call(
           args => [ 123454321 ],
           on_return => sub {
              my $isprime = shift;
              print "123454321 " . ( $isprime ? "is" : "is not" ) . " a prime number\n";
           },
           on_error => sub {
              print STDERR "Cannot determine if it's prime - $_[0]\n";
           },
        );

        $loop->run;

DESCRIPTION

       This subclass of IO::Async::Notifier wraps a function body in a collection of worker
       processes, to allow it to execute independently of the main process.  The object acts as a
       proxy to the function, allowing invocations to be made by passing in arguments, and
       invoking a continuation in the main process when the function returns.

       The object represents the function code itself, rather than one specific invocation of it.
       It can be called multiple times, by the "call" method.  Multiple outstanding invocations
       can be called; they will be dispatched in the order they were queued. If only one worker
       process is used then results will be returned in the order they were called. If multiple
       are used, then each request will be sent in the order called, but timing differences
       between each worker may mean results are returned in a different order.

       Since the code block will be called multiple times within the same child process, it must
       take care not to modify any of its state that might affect subsequent calls. Since it
       executes in a child process, it cannot make any modifications to the state of the parent
       program. Therefore, all the data required to perform its task must be represented in the
       call arguments, and all of the result must be represented in the return values.

       The Function object is implemented using an IO::Async::Routine with two IO::Async::Channel
       objects to pass calls into and results out from it.

       The "IO::Async" framework generally provides mechanisms for multiplexing IO tasks between
       different handles, so there aren't many occasions when such an asynchronous function is
       necessary. Two cases where this does become useful are:

       1.  When a large amount of computationally-intensive work needs to be performed (for
           example, the "is_prime" test in the example in the "SYNOPSIS").

       2.  When a blocking OS syscall or library-level function needs to be called, and no
           nonblocking or asynchronous version is supplied. This is used by
           "IO::Async::Resolver".

       This object is ideal for representing "pure" functions; that is, blocks of code which have
       no stateful effect on the process, and whose result depends only on the arguments passed
       in. For a more general co-routine ability, see also IO::Async::Routine.

PARAMETERS

       The following named parameters may be passed to "new" or "configure":

       code => CODE
               The body of the function to execute.

       model => "spawn" | "thread"
               Optional. Requests a specific "IO::Async::Routine" model. If not supplied, leaves
               the default choice up to Routine.

       min_workers => INT
       max_workers => INT
               The lower and upper bounds of worker processes to try to keep running. The actual
               number running at any time will be kept somewhere between these bounds according
               to load.

       max_worker_calls => INT
               Optional. If provided, stop a worker process after it has processed this number of
               calls. (New workers may be started to replace stopped ones, within the bounds
               given above).

       idle_timeout => NUM
               Optional. If provided, idle worker processes will be shut down after this amount
               of time, if there are more than "min_workers" of them.

       exit_on_die => BOOL
               Optional boolean, controls what happens after the "code" throws an exception. If
               missing or false, the worker will continue running to process more requests. If
               true, the worker will be shut down. A new worker might be constructed by the
               "call" method to replace it, if necessary.

       setup => ARRAY
               Optional array reference. Specifies the "setup" key to pass to the underlying
               IO::Async::Process when setting up new worker processes.

METHODS

   $function->start
       Start the worker processes

   $function->stop
       Stop the worker processes

   $function->restart
       Gracefully stop and restart all the worker processes.

   $function->call( %params )
       Schedules an invocation of the contained function to be executed on one of the worker
       processes. If a non-busy worker is available now, it will be called immediately. If not,
       it will be queued and sent to the next free worker that becomes available.

       The request will already have been serialised by the marshaller, so it will be safe to
       modify any referenced data structures in the arguments after this call returns.

       The %params hash takes the following keys:

       args => ARRAY
               A reference to the array of arguments to pass to the code.

       on_result => CODE
               A continuation that is invoked when the code has been executed. If the code
               returned normally, it is called as:

                $on_result->( 'return', @values )

               If the code threw an exception, or some other error occured such as a closed
               connection or the process died, it is called as:

                $on_result->( 'error', $exception_name )

       on_return => CODE and on_error => CODE
               An alternative to "on_result". Two continuations to use in either of the
               circumstances given above. They will be called directly, without the leading
               'return' or 'error' value.

   $future = $function->call( %params )
       When returning a future, the "on_result", "on_return" and "on_error" continuations are
       optional.

   $count = $function->workers
       Returns the total number of worker processes available

   $count = $function->workers_busy
       Returns the number of worker processes that are currently busy

   $count = $function->workers_idle
       Returns the number of worker processes that are currently idle

NOTES

       For the record, 123454321 is 11111 * 11111, a square number, and therefore not prime.

AUTHOR

       Paul Evans <leonerd@leonerd.org.uk>