[ViewVC] Annotation of: cvs/AnyEvent-Fork/README

NAME
    AnyEvent::Fork - everything you wanted to use fork() for, but couldn't

    ATTENTION, this is a very early release, and very untested. Consider it
    a technology preview.

SYNOPSIS
       use AnyEvent::Fork;

       ##################################################################
       # create a single new process, tell it to run your worker function

       AnyEvent::Fork
          ->new
          ->require ("MyModule")
          ->run ("MyModule::worker, sub {
             my ($master_filehandle) = @_;

             # now $master_filehandle is connected to the
             # $slave_filehandle in the new process.
          });

       # MyModule::worker might look like this
       sub MyModule::worker {
          my ($slave_filehandle) = @_;

          # now $slave_filehandle is connected to the $master_filehandle
          # in the original prorcess. have fun!
       }

       ##################################################################
       # create a pool of server processes all accepting on the same socket

       # create listener socket
       my $listener = ...;

       # create a pool template, initialise it and give it the socket
       my $pool = AnyEvent::Fork
                     ->new
                     ->require ("Some::Stuff", "My::Server")
                     ->send_fh ($listener);

       # now create 10 identical workers
       for my $id (1..10) {
          $pool
             ->fork
             ->send_arg ($id)
             ->run ("My::Server::run");
       }

       # now do other things - maybe use the filehandle provided by run
       # to wait for the processes to die. or whatever.

       # My::Server::run might look like this
       sub My::Server::run {
          my ($slave, $listener, $id) = @_;

          close $slave; # we do not use the socket, so close it to save resources

          # we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
          # or anything we usually couldn't do in a process forked normally.
          while (my $socket = $listener->accept) {
             # do sth. with new socket
          }
       }

DESCRIPTION
    This module allows you to create new processes, without actually forking
    them from your current process (avoiding the problems of forking), but
    preserving most of the advantages of fork.

    It can be used to create new worker processes or new independent
    subprocesses for short- and long-running jobs, process pools (e.g. for
    use in pre-forked servers) but also to spawn new external processes
    (such as CGI scripts from a webserver), which can be faster (and more
    well behaved) than using fork+exec in big processes.

    Special care has been taken to make this module useful from other
    modules, while still supporting specialised environments such as
    App::Staticperl or PAR::Packer.

PROBLEM STATEMENT
    There are two ways to implement parallel processing on UNIX like
    operating systems - fork and process, and fork+exec and process. They
    have different advantages and disadvantages that I describe below,
    together with how this module tries to mitigate the disadvantages.

    Forking from a big process can be very slow (a 5GB process needs 0.05s
    to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead is
    often shared with exec (because you have to fork first), but in some
    circumstances (e.g. when vfork is used), fork+exec can be much faster.
        This module can help here by telling a small(er) helper process to
        fork, or fork+exec instead.

    Forking usually creates a copy-on-write copy of the parent process.
    Memory (for example, modules or data files that have been will not take
    additional memory). When exec'ing a new process, modules and data files
    might need to be loaded again, at extra cpu and memory cost. Likewise
    when forking, all data structures are copied as well - if the program
    frees them and replaces them by new data, the child processes will
    retain the memory even if it isn't used.
        This module allows the main program to do a controlled fork, and
        allows modules to exec processes safely at any time. When creating a
        custom process pool you can take advantage of data sharing via fork
        without risking to share large dynamic data structures that will
        blow up child memory usage.

    Exec'ing a new perl process might be difficult and slow. For example, it
    is not easy to find the correct path to the perl interpreter, and all
    modules have to be loaded from disk again. Long running processes might
    run into problems when perl is upgraded for example.
        This module supports creating pre-initialised perl processes to be
        used as template, and also tries hard to identify the correct path
        to the perl interpreter. With a cooperative main program, exec'ing
        the interpreter might not even be necessary.

    Forking might be impossible when a program is running. For example,
    POSIX makes it almost impossible to fork from a multithreaded program
    and do anything useful in the child - strictly speaking, if your perl
    program uses posix threads (even indirectly via e.g. IO::AIO or
    threads), you cannot call fork on the perl level anymore, at all.
        This module can safely fork helper processes at any time, by caling
        fork+exec in C, in a POSIX-compatible way.

    Parallel processing with fork might be inconvenient or difficult to
    implement. For example, when a program uses an event loop and creates
    watchers it becomes very hard to use the event loop from a child
    program, as the watchers already exist but are only meaningful in the
    parent. Worse, a module might want to use such a system, not knowing
    whether another module or the main program also does, leading to
    problems.
        This module only lets the main program create pools by forking
        (because only the main program can know when it is still safe to do
        so) - all other pools are created by fork+exec, after which such
        modules can again be loaded.

CONCEPTS
    This module can create new processes either by executing a new perl
    process, or by forking from an existing "template" process.

    Each such process comes with its own file handle that can be used to
    communicate with it (it's actually a socket - one end in the new
    process, one end in the main process), and among the things you can do
    in it are load modules, fork new processes, send file handles to it, and
    execute functions.

    There are multiple ways to create additional processes to execute some
    jobs:

    fork a new process from the "default" template process, load code, run
    it
        This module has a "default" template process which it executes when
        it is needed the first time. Forking from this process shares the
        memory used for the perl interpreter with the new process, but
        loading modules takes time, and the memory is not shared with
        anything else.

        This is ideal for when you only need one extra process of a kind,
        with the option of starting and stipping it on demand.

        Example:

           AnyEvent::Fork
              ->new
              ->require ("Some::Module")
              ->run ("Some::Module::run", sub {
                 my ($fork_fh) = @_;
              });

    fork a new template process, load code, then fork processes off of it
    and run the code
        When you need to have a bunch of processes that all execute the same
        (or very similar) tasks, then a good way is to create a new template
        process for them, loading all the modules you need, and then create
        your worker processes from this new template process.

        This way, all code (and data structures) that can be shared (e.g.
        the modules you loaded) is shared between the processes, and each
        new process consumes relatively little memory of its own.

        The disadvantage of this approach is that you need to create a
        template process for the sole purpose of forking new processes from
        it, but if you only need a fixed number of proceses you can create
        them, and then destroy the template process.

        Example:

           my $template = AnyEvent::Fork->new->require ("Some::Module");
   
           for (1..10) {
              $template->fork->run ("Some::Module::run", sub {
                 my ($fork_fh) = @_;
              });
           }

           # at this point, you can keep $template around to fork new processes
           # later, or you can destroy it, which causes it to vanish.

    execute a new perl interpreter, load some code, run it
        This is relatively slow, and doesn't allow you to share memory
        between multiple processes.

        The only advantage is that you don't have to have a template process
        hanging around all the time to fork off some new processes, which
        might be an advantage when there are long time spans where no extra
        processes are needed.

        Example:

           AnyEvent::Fork
              ->new_exec
              ->require ("Some::Module")
              ->run ("Some::Module::run", sub {
                 my ($fork_fh) = @_;
              });

FUNCTIONS
    my $pool = new AnyEvent::Fork key => value...
        Create a new process pool. The following named parameters are
        supported:

    my $proc = new AnyEvent::Fork
        Create a new "empty" perl interpreter process and returns its
        process object for further manipulation.

        The new process is forked from a template process that is kept
        around for this purpose. When it doesn't exist yet, it is created by
        a call to "new_exec" and kept around for future calls.

        When the process object is destroyed, it will release the file
        handle that connects it with the new process. When the new process
        has not yet called "run", then the process will exit. Otherwise,
        what happens depends entirely on the code that is executed.

    $new_proc = $proc->fork
        Forks $proc, creating a new process, and returns the process object
        of the new process.

        If any of the "send_" functions have been called before fork, then
        they will be cloned in the child. For example, in a pre-forked
        server, you might "send_fh" the listening socket into the template
        process, and then keep calling "fork" and "run".

    my $proc = new_exec AnyEvent::Fork
        Create a new "empty" perl interpreter process and returns its
        process object for further manipulation.

        Unlike the "new" method, this method *always* spawns a new perl
        process (except in some cases, see AnyEvent::Fork::Early for
        details). This reduces the amount of memory sharing that is
        possible, and is also slower.

        You should use "new" whenever possible, except when having a
        template process around is unacceptable.

        The path to the perl interpreter is divined usign various methods -
        first $^X is investigated to see if the path ends with something
        that sounds as if it were the perl interpreter. Failing this, the
        module falls back to using $Config::Config{perlpath}.

    $proc = $proc->eval ($perlcode, @args)
        Evaluates the given $perlcode as ... perl code, while setting @_ to
        the strings specified by @args.

        This call is meant to do any custom initialisation that might be
        required (for example, the "require" method uses it). It's not
        supposed to be used to completely take over the process, use "run"
        for that.

        The code will usually be executed after this call returns, and there
        is no way to pass anything back to the calling process. Any
        evaluation errors will be reported to stderr and cause the process
        to exit.

        Returns the process object for easy chaining of method calls.

    $proc = $proc->require ($module, ...)
        Tries to load the given module(s) into the process

        Returns the process object for easy chaining of method calls.

    $proc = $proc->send_fh ($handle, ...)
        Send one or more file handles (*not* file descriptors) to the
        process, to prepare a call to "run".

        The process object keeps a reference to the handles until this is
        done, so you must not explicitly close the handles. This is most
        easily accomplished by simply not storing the file handles anywhere
        after passing them to this method.

        Returns the process object for easy chaining of method calls.

        Example: pass an fh to a process, and release it without closing. it
        will be closed automatically when it is no longer used.

           $proc->send_fh ($my_fh);
           undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT

    $proc = $proc->send_arg ($string, ...)
        Send one or more argument strings to the process, to prepare a call
        to "run". The strings can be any octet string.

        Returns the process object for easy chaining of emthod calls.

    $proc->run ($func, $cb->($fh))
        Enter the function specified by the fully qualified name in $func in
        the process. The function is called with the communication socket as
        first argument, followed by all file handles and string arguments
        sent earlier via "send_fh" and "send_arg" methods, in the order they
        were called.

        If the called function returns, the process exits.

        Preparing the process can take time - when the process is ready, the
        callback is invoked with the local communications socket as
        argument.

        The process object becomes unusable on return from this function.

        If the communication socket isn't used, it should be closed on both
        sides, to save on kernel memory.

        The socket is non-blocking in the parent, and blocking in the newly
        created process. The close-on-exec flag is set on both. Even if not
        used otherwise, the socket can be a good indicator for the existance
        of the process - if the other process exits, you get a readable
        event on it, because exiting the process closes the socket (if it
        didn't create any children using fork).

        Example: create a template for a process pool, pass a few strings,
        some file handles, then fork, pass one more string, and run some
        code.

           my $pool = AnyEvent::Fork
                         ->new
                         ->send_arg ("str1", "str2")
                         ->send_fh ($fh1, $fh2);

           for (1..2) {
              $pool
                 ->fork
                 ->send_arg ("str3")
                 ->run ("Some::function", sub {
                    my ($fh) = @_;

                    # fh is nonblocking, but we trust that the OS can accept these
                    # extra 3 octets anyway.
                    syswrite $fh, "hi #$_\n";

                    # $fh is being closed here, as we don't store it anywhere
                 });
           }

           # Some::function might look like this - all parameters passed before fork
           # and after will be passed, in order, after the communications socket.
           sub Some::function {
              my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;

              print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"
           }

PORTABILITY NOTES
    Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a
    nop, and ::Template is not going to work), and it cost a lot of blood
    and sweat to make it so, mostly due to the bloody broken perl that
    nobody seems to care about. The fork emulation is a bad joke - I have
    yet to see something useful that you cna do with it without running into
    memory corruption issues or other braindamage. Hrrrr.

    Cygwin perl is not supported at the moment, as it should implement fd
    passing, but doesn't, and rolling my own is hard, as cygwin doesn't
    support enough functionality to do it.

AUTHOR
     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de/

Revision:	1.2
Committed:	Thu Apr 4 07:27:09 2013 UTC (11 years, 1 month ago) by root
Branch:	MAIN
CVS Tags:	rel-0_01
Changes since 1.1:	+377 -0 lines
Log Message:	0.01
#	User	Rev	Content
1	root	1.2	NAME
2			AnyEvent::Fork - everything you wanted to use fork() for, but couldn't
3
4			ATTENTION, this is a very early release, and very untested. Consider it
5			a technology preview.
6
7			SYNOPSIS
8			use AnyEvent::Fork;
9
10			##################################################################
11			# create a single new process, tell it to run your worker function
12
13			AnyEvent::Fork
14			->new
15			->require ("MyModule")
16			->run ("MyModule::worker, sub {
17			my ($master_filehandle) = @_;
18
19			# now $master_filehandle is connected to the
20			# $slave_filehandle in the new process.
21			});
22
23			# MyModule::worker might look like this
24			sub MyModule::worker {
25			my ($slave_filehandle) = @_;
26
27			# now $slave_filehandle is connected to the $master_filehandle
28			# in the original prorcess. have fun!
29			}
30
31			##################################################################
32			# create a pool of server processes all accepting on the same socket
33
34			# create listener socket
35			my $listener = ...;
36
37			# create a pool template, initialise it and give it the socket
38			my $pool = AnyEvent::Fork
39			->new
40			->require ("Some::Stuff", "My::Server")
41			->send_fh ($listener);
42
43			# now create 10 identical workers
44			for my $id (1..10) {
45			$pool
46			->fork
47			->send_arg ($id)
48			->run ("My::Server::run");
49			}
50
51			# now do other things - maybe use the filehandle provided by run
52			# to wait for the processes to die. or whatever.
53
54			# My::Server::run might look like this
55			sub My::Server::run {
56			my ($slave, $listener, $id) = @_;
57
58			close $slave; # we do not use the socket, so close it to save resources
59
60			# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
61			# or anything we usually couldn't do in a process forked normally.
62			while (my $socket = $listener->accept) {
63			# do sth. with new socket
64			}
65			}
66
67			DESCRIPTION
68			This module allows you to create new processes, without actually forking
69			them from your current process (avoiding the problems of forking), but
70			preserving most of the advantages of fork.
71
72			It can be used to create new worker processes or new independent
73			subprocesses for short- and long-running jobs, process pools (e.g. for
74			use in pre-forked servers) but also to spawn new external processes
75			(such as CGI scripts from a webserver), which can be faster (and more
76			well behaved) than using fork+exec in big processes.
77
78			Special care has been taken to make this module useful from other
79			modules, while still supporting specialised environments such as
80			App::Staticperl or PAR::Packer.
81
82			PROBLEM STATEMENT
83			There are two ways to implement parallel processing on UNIX like
84			operating systems - fork and process, and fork+exec and process. They
85			have different advantages and disadvantages that I describe below,
86			together with how this module tries to mitigate the disadvantages.
87
88			Forking from a big process can be very slow (a 5GB process needs 0.05s
89			to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead is
90			often shared with exec (because you have to fork first), but in some
91			circumstances (e.g. when vfork is used), fork+exec can be much faster.
92			This module can help here by telling a small(er) helper process to
93			fork, or fork+exec instead.
94
95			Forking usually creates a copy-on-write copy of the parent process.
96			Memory (for example, modules or data files that have been will not take
97			additional memory). When exec'ing a new process, modules and data files
98			might need to be loaded again, at extra cpu and memory cost. Likewise
99			when forking, all data structures are copied as well - if the program
100			frees them and replaces them by new data, the child processes will
101			retain the memory even if it isn't used.
102			This module allows the main program to do a controlled fork, and
103			allows modules to exec processes safely at any time. When creating a
104			custom process pool you can take advantage of data sharing via fork
105			without risking to share large dynamic data structures that will
106			blow up child memory usage.
107
108			Exec'ing a new perl process might be difficult and slow. For example, it
109			is not easy to find the correct path to the perl interpreter, and all
110			modules have to be loaded from disk again. Long running processes might
111			run into problems when perl is upgraded for example.
112			This module supports creating pre-initialised perl processes to be
113			used as template, and also tries hard to identify the correct path
114			to the perl interpreter. With a cooperative main program, exec'ing
115			the interpreter might not even be necessary.
116
117			Forking might be impossible when a program is running. For example,
118			POSIX makes it almost impossible to fork from a multithreaded program
119			and do anything useful in the child - strictly speaking, if your perl
120			program uses posix threads (even indirectly via e.g. IO::AIO or
121			threads), you cannot call fork on the perl level anymore, at all.
122			This module can safely fork helper processes at any time, by caling
123			fork+exec in C, in a POSIX-compatible way.
124
125			Parallel processing with fork might be inconvenient or difficult to
126			implement. For example, when a program uses an event loop and creates
127			watchers it becomes very hard to use the event loop from a child
128			program, as the watchers already exist but are only meaningful in the
129			parent. Worse, a module might want to use such a system, not knowing
130			whether another module or the main program also does, leading to
131			problems.
132			This module only lets the main program create pools by forking
133			(because only the main program can know when it is still safe to do
134			so) - all other pools are created by fork+exec, after which such
135			modules can again be loaded.
136
137			CONCEPTS
138			This module can create new processes either by executing a new perl
139			process, or by forking from an existing "template" process.
140
141			Each such process comes with its own file handle that can be used to
142			communicate with it (it's actually a socket - one end in the new
143			process, one end in the main process), and among the things you can do
144			in it are load modules, fork new processes, send file handles to it, and
145			execute functions.
146
147			There are multiple ways to create additional processes to execute some
148			jobs:
149
150			fork a new process from the "default" template process, load code, run
151			it
152			This module has a "default" template process which it executes when
153			it is needed the first time. Forking from this process shares the
154			memory used for the perl interpreter with the new process, but
155			loading modules takes time, and the memory is not shared with
156			anything else.
157
158			This is ideal for when you only need one extra process of a kind,
159			with the option of starting and stipping it on demand.
160
161			Example:
162
163			AnyEvent::Fork
164			->new
165			->require ("Some::Module")
166			->run ("Some::Module::run", sub {
167			my ($fork_fh) = @_;
168			});
169
170			fork a new template process, load code, then fork processes off of it
171			and run the code
172			When you need to have a bunch of processes that all execute the same
173			(or very similar) tasks, then a good way is to create a new template
174			process for them, loading all the modules you need, and then create
175			your worker processes from this new template process.
176
177			This way, all code (and data structures) that can be shared (e.g.
178			the modules you loaded) is shared between the processes, and each
179			new process consumes relatively little memory of its own.
180
181			The disadvantage of this approach is that you need to create a
182			template process for the sole purpose of forking new processes from
183			it, but if you only need a fixed number of proceses you can create
184			them, and then destroy the template process.
185
186			Example:
187
188			my $template = AnyEvent::Fork->new->require ("Some::Module");
189
190			for (1..10) {
191			$template->fork->run ("Some::Module::run", sub {
192			my ($fork_fh) = @_;
193			});
194			}
195
196			# at this point, you can keep $template around to fork new processes
197			# later, or you can destroy it, which causes it to vanish.
198
199			execute a new perl interpreter, load some code, run it
200			This is relatively slow, and doesn't allow you to share memory
201			between multiple processes.
202
203			The only advantage is that you don't have to have a template process
204			hanging around all the time to fork off some new processes, which
205			might be an advantage when there are long time spans where no extra
206			processes are needed.
207
208			Example:
209
210			AnyEvent::Fork
211			->new_exec
212			->require ("Some::Module")
213			->run ("Some::Module::run", sub {
214			my ($fork_fh) = @_;
215			});
216
217			FUNCTIONS
218			my $pool = new AnyEvent::Fork key => value...
219			Create a new process pool. The following named parameters are
220			supported:
221
222			my $proc = new AnyEvent::Fork
223			Create a new "empty" perl interpreter process and returns its
224			process object for further manipulation.
225
226			The new process is forked from a template process that is kept
227			around for this purpose. When it doesn't exist yet, it is created by
228			a call to "new_exec" and kept around for future calls.
229
230			When the process object is destroyed, it will release the file
231			handle that connects it with the new process. When the new process
232			has not yet called "run", then the process will exit. Otherwise,
233			what happens depends entirely on the code that is executed.
234
235			$new_proc = $proc->fork
236			Forks $proc, creating a new process, and returns the process object
237			of the new process.
238
239			If any of the "send_" functions have been called before fork, then
240			they will be cloned in the child. For example, in a pre-forked
241			server, you might "send_fh" the listening socket into the template
242			process, and then keep calling "fork" and "run".
243
244			my $proc = new_exec AnyEvent::Fork
245			Create a new "empty" perl interpreter process and returns its
246			process object for further manipulation.
247
248			Unlike the "new" method, this method always spawns a new perl
249			process (except in some cases, see AnyEvent::Fork::Early for
250			details). This reduces the amount of memory sharing that is
251			possible, and is also slower.
252
253			You should use "new" whenever possible, except when having a
254			template process around is unacceptable.
255
256			The path to the perl interpreter is divined usign various methods -
257			first $^X is investigated to see if the path ends with something
258			that sounds as if it were the perl interpreter. Failing this, the
259			module falls back to using $Config::Config{perlpath}.
260
261			$proc = $proc->eval ($perlcode, @args)
262			Evaluates the given $perlcode as ... perl code, while setting @_ to
263			the strings specified by @args.
264
265			This call is meant to do any custom initialisation that might be
266			required (for example, the "require" method uses it). It's not
267			supposed to be used to completely take over the process, use "run"
268			for that.
269
270			The code will usually be executed after this call returns, and there
271			is no way to pass anything back to the calling process. Any
272			evaluation errors will be reported to stderr and cause the process
273			to exit.
274
275			Returns the process object for easy chaining of method calls.
276
277			$proc = $proc->require ($module, ...)
278			Tries to load the given module(s) into the process
279
280			Returns the process object for easy chaining of method calls.
281
282			$proc = $proc->send_fh ($handle, ...)
283			Send one or more file handles (not file descriptors) to the
284			process, to prepare a call to "run".
285
286			The process object keeps a reference to the handles until this is
287			done, so you must not explicitly close the handles. This is most
288			easily accomplished by simply not storing the file handles anywhere
289			after passing them to this method.
290
291			Returns the process object for easy chaining of method calls.
292
293			Example: pass an fh to a process, and release it without closing. it
294			will be closed automatically when it is no longer used.
295
296			$proc->send_fh ($my_fh);
297			undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
298
299			$proc = $proc->send_arg ($string, ...)
300			Send one or more argument strings to the process, to prepare a call
301			to "run". The strings can be any octet string.
302
303			Returns the process object for easy chaining of emthod calls.
304
305			$proc->run ($func, $cb->($fh))
306			Enter the function specified by the fully qualified name in $func in
307			the process. The function is called with the communication socket as
308			first argument, followed by all file handles and string arguments
309			sent earlier via "send_fh" and "send_arg" methods, in the order they
310			were called.
311
312			If the called function returns, the process exits.
313
314			Preparing the process can take time - when the process is ready, the
315			callback is invoked with the local communications socket as
316			argument.
317
318			The process object becomes unusable on return from this function.
319
320			If the communication socket isn't used, it should be closed on both
321			sides, to save on kernel memory.
322
323			The socket is non-blocking in the parent, and blocking in the newly
324			created process. The close-on-exec flag is set on both. Even if not
325			used otherwise, the socket can be a good indicator for the existance
326			of the process - if the other process exits, you get a readable
327			event on it, because exiting the process closes the socket (if it
328			didn't create any children using fork).
329
330			Example: create a template for a process pool, pass a few strings,
331			some file handles, then fork, pass one more string, and run some
332			code.
333
334			my $pool = AnyEvent::Fork
335			->new
336			->send_arg ("str1", "str2")
337			->send_fh ($fh1, $fh2);
338
339			for (1..2) {
340			$pool
341			->fork
342			->send_arg ("str3")
343			->run ("Some::function", sub {
344			my ($fh) = @_;
345
346			# fh is nonblocking, but we trust that the OS can accept these
347			# extra 3 octets anyway.
348			syswrite $fh, "hi #$_\n";
349
350			# $fh is being closed here, as we don't store it anywhere
351			});
352			}
353
354			# Some::function might look like this - all parameters passed before fork
355			# and after will be passed, in order, after the communications socket.
356			sub Some::function {
357			my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
358
359			print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"
360			}
361
362			PORTABILITY NOTES
363			Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a
364			nop, and ::Template is not going to work), and it cost a lot of blood
365			and sweat to make it so, mostly due to the bloody broken perl that
366			nobody seems to care about. The fork emulation is a bad joke - I have
367			yet to see something useful that you cna do with it without running into
368			memory corruption issues or other braindamage. Hrrrr.
369
370			Cygwin perl is not supported at the moment, as it should implement fd
371			passing, but doesn't, and rolling my own is hard, as cygwin doesn't
372			support enough functionality to do it.
373
374			AUTHOR
375			Marc Lehmann <schmorp@schmorp.de>
376			http://home.schmorp.de/
377