package Async; $VERSION = '0.10'; sub new { my ($pack, $task) = @_; my $r = \ do {local *FH}; my $w = \ do {local *FH}; unless (pipe $r, $w) { $ERROR = "Couldn't make pipe: $!"; return; } my $pid = fork(); unless (defined $pid) { $ERROR = "Couldn't fork: $!"; return; } if ($pid) { # parent close $w; my $self = { TASK => $task, PID => $pid, PIPE => $r, FD => fileno($r), DATA => '', }; bless $self => $pack; } else { # child close $r; my $result = $task->(); print $w $result; exit 0; } } # return true iff async process is complete # with true `$force' argmuent, wait until process is complete before returning sub ready { my ($self, $force) = @_; my $timeout; $timeout = 0 unless $force; return 1 if $self->{FINISHED}; my $fdset = ''; vec($fdset, $self->{FD}, 1) = 1; while (select($fdset, undef, undef, $timeout)) { my $buf; my $nr = read $self->{PIPE}, $buf, 8192; if ($nr) { $self->{DATA} .= $buf; } elsif (defined $nr) { # EOF $self->{FINISHED} = 1; return 1; } else { $self->{ERROR} = "Read error: $!"; $self->{FINISHED} = 1; return 1; } } return 0; } # Return error message if an error occurred # Return false if no error occurred sub error { $_[0]{ERROR}; } # Return resulting data if async process is complete # return undef if it is incopmplete # a true $force argument waits for the process to complete before returning sub result { my ($self, $force) = @_; if ($self->{FINISHED}) { $self->{DATA}; } elsif ($force) { $self->ready('force completion'); $self->{DATA}; } else { return; } } sub DESTROY { my ($self) = @_; my $pid = $self->{PID}; kill 9 => $pid; # I don't care. waitpid($pid, 0); } package AsyncTimeout; @ISA = 'Async'; sub new { my ($pack, $task, $timeout, $msg) = @_; $msg = "Timed out\n" unless defined $msg; my $newtask = sub { local $SIG{ALRM} = sub { die "TIMEOUT\n" }; alarm $timeout; my $s = eval {$task->()}; return $msg if !defined($s) && $@ eq "TIMEOUT\n"; return $s; }; my $self = Async->new($newtask); return unless $self; bless $self => AsyncTimeout; } package AsyncData; @ISA = 'Async'; sub new { require Storable; my ($pack, $task) = @_; my $newtask = sub { my $v = $task->(); return Storable::freeze($v); }; my $self = Async->new($newtask); return unless $self; bless $self => AsyncData; } sub result { require Storable; my $self = shift; my $rc = $self->SUPER::result(@_); return defined $rc ? Storable::thaw($rc) : $rc; } 1; =head1 NAME Async - Asynchronous evaluation of Perl code (with optional timeouts) =head1 SYNOPSIS my $proc = Async->new(sub { any perl code you want executed }); if ($proc->ready) { # the code has finished executing if ($proc->error) { # something went wrong } else { $result = $proc->result; # The return value of the code } } # or: $result = $proc->result('force completion'); # wait for it to finish =head1 DESCRIPTION C executes some code in a separate process and retrieves the result. Since the code is running in a separate process, your main program can continue with whatever it was doing while the separate code is executing. This separate code is called an `asynchronous computation'. When your program wants to check to see if the asynchronous computation is complete, it can call the C method, which returns true if so, and false if it is still running. After the asynchronous computation is complete, you should call the C method to make sure that everything went all right. C will return C if the computation completed normally, and an error message otherwise. Data returned by the computation can be retrieved with the C method. The data must be a single string; any non-string value returned by the computation will be stringized. (See AsyncData below for how to avoid this.) If the computation has not completed yet, C will return an undefined value. C takes an optional parameter, C<$force>. If C<$force> is true, then the calling process will wait until the asynchronous computation is complete before returning. =head2 C use Async; $proc = AsyncTimeout->new(sub {...}, $timeout, $special); C implements a version of C that has an automatic timeout. If the asynchronous computation does not complete before C<$timeout> seconds have elapsed, it is forcibly terminated and returns a special value C<$special>. The default special value is the string "Timed out\n". All the other methods for C are exactly the same as for C. =head2 C use Async; $proc = AsyncData->new(sub {...}); C is just like C except that instead of returning a string, the asynchronous computation may return any scalar value. If the scalar value is a reference, the C method will yield a refernce to a copy of this data structure. The C module requires that C be installed. C will die if C is unavailable. All the other methods for C are exactly the same as for C. =head1 WARNINGS FOR THE PROGRAMMER The asynchronous computation takes place in a separate process, so nothing it does can affect the main program. For example, if it modifies global variables, changes the current directory, opens and closes filehandles, or calls C, the parent process will be unaware of these things. However, the asynchronous computatin does inherit the main program's file handles, so if it reads data from files that the main program had open, that data will not be availble to the main program; similarly the asynchronous computation can write data to the same file as the main program if it inherits an open filehandle for that file. =head1 ERRORS The errors that are reported by the C mechanism are: those that are internal to C itself: Couldn't make pipe: (reason) Couldn't fork: (reason) Read error: (reason) If your asynchronous computation dies for any reason, that is not considered to be an `error'; that is the normal termination of the process. Any messages written to C will go to the computation's C, which is normally inherited from the main program, and the C will be the empty string. =head1 EXAMPLE use Async; sub long_running_computation { # This function simulates a computation that takes a long time to run my ($x) = @_; sleep 5; return $x+2; # Eureka! } # Main program: my $proc = Async->new(sub {long_running_computation(2)}) or die; # The long-running computation is now executing. # while (1) { print "Main program: The time is now ", scalar(localtime), "\n"; my $e; if ($proc->ready) { if ($e = $proc->error) { print "Something went wrong. The error was: $e\n"; } else { print "The result of the computation is: ", $proc->result, "\n"; } undef $proc; } # The result is not ready; we can go off and do something else here. sleep 1; # One thing we could do is to take nap. } =head1 AUTHOR Mark-Jason Dominus C. =cut