Apache::SubProcess -- Executing SubProcesses under mod_perl


Apache::SubProcess -- Executing SubProcesses under mod_perl


  use Apache::SubProcess ();

  use Config;
  use constant PERLIO_IS_ENABLED => $Config{useperlio};

  # pass @ARGV / read from the process
  $command = "/tmp/argv.pl";
  @argv = qw(foo bar);
  $out_fh = $r->spawn_proc_prog($command, \@argv);
  $output = read_data($out_fh);

  # pass environment / read from the process
  $command = "/tmp/env.pl";
  $r->subprocess_env->set(foo => "bar");
  $out_fh = $r->spawn_proc_prog($command);
  $output = read_data($out_fh);

  # write to/read from the process
  $command = "/tmp/in_out_err.pl";
  ($in_fh, $out_fh, $err_fh) = $r->spawn_proc_prog($command);
  print $in_fh "hello\n";
  $output = read_data($out_fh);
  $error  = read_data($err_fh);

  # helper function to work w/ and w/o perlio-enabled Perl
  sub read_data {
      my($fh) = @_;
      my $data;
      if (PERLIO_IS_ENABLED || IO::Select->new($fh)->can_read(10)) {
          $data = <$fh>;
      return defined $data ? $data : '';


Apache::SubProcess provides the Perl API for running and communicating with processes spawned from mod_perl handlers.

At the moment it's possible to spawn only external program in a new process. It's possible to provide other interfaces, e.g. executing a sub-routine reference (via B::Deparse) and may be spawn a new program in a thread (since the APR api includes API for spawning threads, e.g. that's how it's running mod_cgi on win32).



Spawn a sub-process and return STD communication pipes:

  $out_fh                    = $r->spawn_proc_prog($command);
  $out_fh                    = $r->spawn_proc_prog($command, \@argv);
  ($in_fh, $out_fh, $err_fh) = $r->spawn_proc_prog($command);
  ($in_fh, $out_fh, $err_fh) = $r->spawn_proc_prog($command, \@argv);
obj: $r ( Apache::RequestRec object|docs::2.0::api::Apache::RequestRec )
arg1: $command ( string )
The command to be $exec()'ed.

opt arg2: \@argv ( ARRAY ref )
A reference to an array of arguments to be passed to the process as the process' ARGV.

ret: ...
In SCALAR context returns the output filehandle of the spawned process.

In LIST context returns the input, outpur and error filehandles of the spawned process.

since: 1.99_15

It's possible to pass environment variables as well, by calling:

  $r->subprocess_env->set($key => $value);

before spawning the subprocess.

There is an issue with reading from the read filehandle ($in_fh)):

A pipe filehandle returned under perlio-disabled Perl needs to call select() if the other end is not fast enough to send the data, since the read is non-blocking.

A pipe filehandle returned under perlio-enabled Perl on the other hand does the select() internally, because it's really a filehandle opened via :APR layer, which internally uses APR to communicate with the pipe. The way APR is implemented Perl's select() cannot be used with it (mainly because select() wants fileno() and APR is a crossplatform implementation which hides the internal datastructure).

Therefore to write a portable code, you want to use select for perlio-disabled Perl and do nothing for perlio-enabled Perl, hence you can use something similar to the read_data() wrapper shown in the Synopsis section.

Several examples appear in the Synopsis section.

See Also

mod_perl 2.0 documentation.


mod_perl 2.0 and its core modules are copyrighted under The Apache Software License, Version 2.0.


The mod_perl development team and numerous contributors.

 Apache::SubProcess -- Executing SubProcesses under mod_perl