== hardwood

Erlang style concurrency for CHICKEN Scheme, heavily inspired by
termite.

'''All the Termite API is currently not implemented and probably never
will. Also, some incompatibilities are to be expected.'''

[[toc:]]

== Requirements

* [[matchable]]
* [[uuid]]

== Bugs and Limitations

* There is currently no support for nodes

== Source code

The code is available in a
[[https://www.upyum.com/cgit.cgi/hardwood/|git repository]]

You can clone it with:
 git clone git://upyum.com/hardwood

== Author

Adrien Ramos, heavily inspired by the Termite project of Guillaume
Germain.

== Documentation

=== Notes

Hardwood processes are implemented as simple srfi-18 threads so they
behave in the same ways. The name {{process}} was chosen as per
Erlang's nomenclature.

As a general rule, mutation should be avoided when using hardwood,
especially inside messages themselves as there is no copy involved.

{{TIMEOUT}} in the following definitions can be (as per srfi-18) either
of the following:

* an srfi-18 time object, which represents an absolute point in time
* a number, which represents a relative time in seconds
* #f for no timeout

If {{DEFAULT}} is specified when {{TIMEOUT}} is, it is returned in case
of timeout. Otherwise {{timeout-condition}} is signaled.

=== Constants

==== timeout-condition

Condition object raised when a timeout is reached.

=== Predicates

==== monitor-ref?

<procedure>(monitor-ref? OBJ)</procedure>

Whether {{obj}} is a monitor reference or not.

==== pid?

<procedure>(pid? OBJ)</procedure>

Whether {{obj}} is a {{pid}} object or not.

==== process-exist?

<procedure>(process-exist? PID)</procedure>

Whether {{pid}} is a running process or not.

==== timeout-condition?

<procedure>(timeout-condition? OBJ)</procedure>

Whether {{obj}} is {{timeout-condition}} or not.

=== Fundamental Operations

==== spawn

<procedure>(spawn PROC . ARGS)</procedure>

Create a process running {{(proc args ...)}} and returns its {{pid}}.

==== self

<procedure>(self)</procedure>

Return the current process' {{pid}}.

==== setup-thread

<procedure>(setup-thread [THREAD])</procedure>

Make {{thread}} a hardwood process.

If given, {{thread}} must be a srfi-18 thread. Otherwise, the current
thread is used.

==== make-tag

<procedure>(make-tag)</procedure>

Return a new {{tag}}.

Tags are guaranteed to be universally unique.

==== monitor

<procedure>(monitor PID)</procedure>

The calling process starts monitoring the {{pid}} process.

Return a monitor reference {{ref}}.

If that process exits, either normally or not, the caller process will
be informed with a message of the form:

{{('DOWN ref pid reason)}}

where {{reason}} can be one of the following:

; symbol {{exited}} : the process exited normally
; symbol {{no-process}} : the process didn't exist
; list {{('condition c)}} : the process exited because of condition {{c}}

==== demonitor

<procedure>(demonitor ref)</procedure>

Stop the monitor associated with {{ref}}.

==== !

<procedure>(! PID MSG)</procedure>

Send {{msg}} to process {{pid}}.

==== !!

<procedure>(!! LIST MSG)</procedure>

{{List}} must be a list of pids.

Send {{msg}} to all pids in {{list}}

==== ?

<syntax>(? [TIMEOUT [DEFAULT]])</syntax>

Fetch the first message from the mailbox.

==== ??

<procedure>(?? PRED [TIMEOUT [DEFAULT]])</procedure>

Fetch the next message that matches {{pred}}.

==== !?

<procedure>(!? PID MSG [TIMEOUT [DEFAULT]])</procedure>

Send {{msg}} to process {{pid}} and wait for a reply.

The actual message sent to {{pid}} is (list (self) tag {{msg}}).

This procedure wait for a reply of the form (list tag {{reply}}) and
returns {{reply}}.

==== recv

<syntax>(recv PAT [...] [(after TIMEOUT TMO-ACTION)])</syntax>

Match incoming messages against {{PAT ...}}.

Each pattern must be a valid pattern for '''[[/egg/matchable|match]]'''.

Optionally, do {{tmo-action}} after {{timeout}}.

'''This version of {{recv}} is incompatible with the one defined in
the Termite paper and implementation as it uses the syntax of the
[[matchable]] egg.'''

== Examples

=== Making the REPL process a hardwood process

Inside csi:
<enscript highlight="scheme">
(use hardwood srfi-18)
(setup-thread)
</enscript>

This can be useful to communicate with other processes from the REPL, as
in the following examples.

=== Making a "server" process

<enscript highlight="scheme">
(use hardwood srfi-18)
(setup-thread)

(define pong-server
  (spawn
    (lambda ()
      (let loop ()
        (recv
          (((? pid? pid) 'ping)  (! pid 'pong)
                                 (loop))
          (else  (loop))))

(! pong-server (list (self) 'ping))

(?)                 --> pong
</enscript>

=== Selective message retrieval

<enscript highlight="scheme">
(use hardwood srfi-18)
(setup-thread)

(! (self) 1)
(! (self) 2)
(! (self) 3)

(?)                 --> 1
(?? odd?)           --> 3
(?)                 --> 2
</enscript>

=== RPC service

<enscript highlight="scheme">
(use hardwood srfi-18)
(setup-thread)

(define rpc-server
  (spawn
    (lambda ()
      (let loop ()
        (recv
          ((from tag ('add a b))
           (! from (list tag (+ a b)))))
        (loop)))))

(!? rpc-server '(add 21 21))      ---> 42
</enscript>

=== Monitoring processes

<enscript highlight="scheme">
(use hardwood srfi-18)
(setup-thread)

(define pid
  (spawn
    (lambda ()
      (recv
        (x  (/ 0)))))))

(define ref (monitor pid))

(! pid 'msg)
(?)                --> ('DOWN ref pid ('condition exn))
</enscript>

== Version History

; 0.5 : setup-thread now uses the current-thread by default, macro helper procedures are not exported from the module anymore (thanks Evan for the patches!)
; 0.4 : Bug fixes; tests now use the [[test]] egg; in-process call history is now more useful
; 0.3 : Bug fix; `!!` function; spawn accepts procedure arguments; monitor references
; 0.2 : Implement process monitoring
; 0.1 : Initial release

== License

 Copyright (c) 2014, Adrien Ramos <kooda@upyum.com>
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are
 met:
 
 1. Redistributions of source code must retain the above copyright
 notice, this list of conditions and the following disclaimer.
 
 2. Redistributions in binary form must reproduce the above copyright
 notice, this list of conditions and the following disclaimer in the
 documentation and/or other materials provided with the distribution.
 
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.