NAME
    Coro::ProcessPool - an asynchronous process pool

SYNOPSIS
        use Coro::ProcessPool;

        my $pool = Coro::ProcessPool->new(
            max_procs => 4,
            max_reqs  => 100,
        );

        my $double = sub { $_[0] * 2 };

        # Process in sequence
        my %result;
        foreach my $i (1 .. 1000) {
            $result{$i} = $pool->process($double, [$i]);
        }

        # Process as a batch
        my @results = $pool->map($double, 1 .. 1000);

        # Defer waiting for result
        my %deferred = map { $_ => $pool->defer($double, [$_]) } 1 .. 1000);
        foreach my $i (keys %deferred) {
            print "$i = " . $deferred{$i}->() . "\n";
        }

        $pool->shutdown;

DESCRIPTION
    Processes tasks using a pool of external Perl processes.

METHODS
  new
    Creates a new process pool. Processes will be spawned as needed.

    max_procs
        This is the maximum number of child processes to maintain. If all
        processes are busy handling tasks, further calls to "process" in .
        will yield until a process becomes available. If not specified,
        defaults to the number of CPUs on the system.

    max_reqs
        If this is a positive number (defaults to 0), child processes will
        be terminated and replaced after handling "max_reqs" tasks. Choosing
        the correct value for "max_reqs" is a tradeoff between the need to
        clear memory leaks in the child process and the time it takes to
        spawn a new process and import any packages used by client code.

  process($f, $args, $timeout)
    Processes code ref $f in a child process from the pool. If $args is
    provided, it is an array ref of arguments that will be passed to $f.
    Returns the result of calling "$f-"(@$args)>.

    This call will yield until the results become available. If all
    processes are busy, this method will block until one becomes available.
    Processes are spawned as needed, up to "max_procs", from this method.
    Also note that the use of "max_reqs" can cause this method to yield
    while a new process is spawned.

    A timeout may be optionally specified in fractional seconds. If
    specified, $timeout will cause "process" to croak if $timeout seconds
    pass an no process becomes available to handle the task.

    Note that the timeout only applies to the time it takes to acquire an
    available process. It does not watch the time it takes to perform the
    task.

  map($f, @args)
    Applies $f to each value in @args in turn and returns a list of the
    results. Although the order in which each argument is processed is not
    guaranteed, the results are guaranteed to be in the same order as @args,
    even if the result of calling $f returns a list itself (in which case,
    the results of that calcuation is flattened into the list returned by
    "map".

  defer($f, $args)
    Similar to "process" in ., but returns immediately. The return value is
    a code reference that, when called, returns the results of calling
    "$f-"(@$args)>.

        my $deferred = $pool->defer($coderef, [ $x, $y, $z ]);
        my $result   = $deferred->();

  shutdown
    Shuts down all processes and resets state on the process pool. After
    calling this method, the pool is effectively in a new state and may be
    used normally.

A NOTE ABOUT IMPORTS AND CLOSURES
    Code refs are serialized using Storable to pass them to the worker
    processes. Once deserialized in the pool process, these functions can no
    longer see the stack as it is in the parent process. Therefore, imports
    and variables external to the function are unavailable.

    Something like this will not work:

        use Foo;
        my $foo = Foo->new();

        my $result = $pool->process(sub {
            return $foo->bar; # $foo not found
        });

    Nor will this:

        use Foo;
        my $result = $pool->process(sub {
            my $foo = Foo->new; # Foo not found
            return $foo->bar;
        });

    The correct way to do this is to import from within the function:

        my $result = $pool->process(sub {
            require Foo;
            my $foo = Foo->new();
            return $foo->bar;
        });

    ...or to pass in external variables that are needed by the function:

        use Foo;
        my $foo = Foo->new();

        my $result = $pool->process(sub { $_[0]->bar }, [ $foo ]);

  Use versus require
    The "use" pragma is run a compile time, whereas "require" is evaluated
    at runtime. Because of this, the use of "use" in code passed directly to
    the "process" method can fail because the "use" statement has already
    been evaluated when the calling code was compiled.

    This will not work:

        $pool->process(sub {
            use Foo;
            my $foo = Foo->new();
        });

    This will work:

        $pool->process(sub {
            require Foo;
            my $foo = Foo->new();
        });

    If "use" is necessary (for example, to import a method or transform the
    calling code via import), it is recommended to move the code into its
    own module, which can then be called in the anonymous routine:

        package Bar;

        use Foo;

        sub dostuff {
            ...
        }

    Then, in your caller:

        $pool->process(sub {
            require Bar;
            Bar::dostuff();
        });

COMPATIBILITY
    "Coro::ProcessPool" will likely break on Win32 due to missing support
    for non-blocking file descriptors (Win32 can only call "select" and
    "poll" on actual network sockets). Without rewriting this as a network
    server, which would impact performance and be really annoying, it is
    likely this module will not support Win32 in the near future.

    The following modules will get you started if you wish to explore a
    synchronous process pool on Windows:

    Win32::Process
    Win32::IPC
    Win32::Pipe

AUTHOR
    Jeff Ober <jeffober@gmail.com>

LICENSE
    BSD License

