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

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.

        @result = $code->( @args )

   init_code => CODE
       Optional. If defined, this is invoked exactly once in every child process or thread, after
       it is created, but before the first invocation of the function body itself.

        $init_code->()

   model => "fork" | "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

       The following methods documented with a trailing call to "->get" return Future instances.

   start
          $function->start

       Start the worker processes

   stop
          $function->stop

       Stop the worker processes

   restart
          $function->restart

       Gracefully stop and restart all the worker processes.

   call
          @result = $function->call( %params )->get

       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.

       If the function body returns normally the list of results are provided as the (successful)
       result of returned future. If the function throws an exception this results in a failed
       future. In the special case that the exception is in fact an unblessed "ARRAY" reference,
       this array is unpacked and used as-is for the "fail" result. If the exception is not such
       a reference, it is used as the first argument to "fail", in the category of "error".

          $f->done( @result )

          $f->fail( @{ $exception } )
          $f->fail( $exception, error => )

   call (void)
          $function->call( %params )

       When not returning a future, the "on_result", "on_return" and "on_error" arguments give
       continuations to handle successful results or failure.

       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 occurred 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.

   workers
          $count = $function->workers

       Returns the total number of worker processes available

   workers_busy
          $count = $function->workers_busy

       Returns the number of worker processes that are currently busy

   workers_idle
          $count = $function->workers_idle

       Returns the number of worker processes that are currently idle

EXAMPLES

   Extended Error Information on Failure
       The array-unpacking form of exception indiciation allows the function body to more
       precicely control the resulting failure from the "call" future.

        my $divider = IO::Async::Function->new(
           code => sub {
              my ( $numerator, $divisor ) = @_;
              $divisor == 0 and
                 die [ "Cannot divide by zero", div_zero => $numerator, $divisor ];

              return $numerator / $divisor;
           }
        );

NOTES

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

AUTHOR

       Paul Evans <leonerd@leonerd.org.uk>