Provided by: libio-async-perl_0.803-1_all 
NAME
"IO::Async::Function" - call a function asynchronously
SYNOPSIS
use Future::AsyncAwait;
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 );
my $isprime = await $function->call(
args => [ 123454321 ],
);
print "123454321 " . ( $isprime ? "is" : "is not" ) . " a prime number\n";
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->();
module => STRING
func => STRING
Since version 0.79.
An alternative to the "code" argument, which names a module to load and a function to call
within it. "module" should give a perl module name (i.e. "Some::Name", not a filename
like Some/Name.pm), and "func" should give the basename of a function within that module
(i.e. without the module name prefixed). It will be invoked, without extra arguments, as
the main code body of the object.
The task of loading this module and resolving the resulting function from it is only
performed on the remote worker side, so the controlling process will not need to actually
load the module.
init_func => STRING or ARRAY [ STRING, ... ]
Optional addition to the "module" and "func" alternatives. Names a function within the
module to call each time a new worker is created.
If this value is an array reference, its first element must be a string giving the name of
the function; the remaining values are passed to that function as arguments.
model => "fork" | "thread" | "spawn"
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 in "await" expressions return Future instances.
start
$function->start;
Start the worker processes
stop
$function->stop;
Stop the worker processes
$f = $function->stop;
Since version 0.75.
If called in non-void context, returns a IO::Async::Future instance that will complete
once every worker process has stopped and exited. This may be useful for waiting until all
of the processes are waited on, or other edge-cases, but is not otherwise particularly
useful.
restart
$function->restart;
Gracefully stop and restart all the worker processes.
call
@result = await $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.
priority => NUM
Optional. Defines the sorting order when no workers are available and calls must
be queued for later. A default of zero will apply if not provided.
Higher values cause the call to be considered more important, and will be placed
earlier in the queue than calls with a smaller value. Calls of equal priority are
still handled in FIFO order.
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>