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.

  1. hardwood
  2. Requirements
  3. Bugs and Limitations
  4. Source code
  5. Author
  6. Documentation
    1. Notes
    2. Constants
      1. timeout-condition
    3. Predicates
      1. monitor-ref?
      2. pid?
      3. process-exist?
      4. timeout-condition?
    4. Fundamental Operations
      1. spawn
      2. self
      3. setup-thread
      4. make-tag
      5. monitor
      6. demonitor
      7. !
      8. !!
      9. ?
      10. ??
      11. !?
      12. recv
  7. Examples
    1. Making the REPL process a hardwood process
    2. Making a "server" process
    3. Selective message retrieval
    4. RPC service
    5. Monitoring processes
  8. Version History
  9. License

Requirements

Bugs and Limitations

Source code

The code is available in a 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:

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)

Whether obj is a monitor reference or not.

pid?

[procedure] (pid? OBJ)

Whether obj is a pid object or not.

process-exist?

[procedure] (process-exist? PID)

Whether pid is a running process or not.

timeout-condition?

[procedure] (timeout-condition? OBJ)

Whether obj is timeout-condition or not.

Fundamental Operations

spawn

[procedure] (spawn PROC . ARGS)

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

self

[procedure] (self)

Return the current process' pid.

setup-thread

[procedure] (setup-thread [THREAD])

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)

Return a new tag.

Tags are guaranteed to be universally unique.

monitor

[procedure] (monitor PID)

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)

Stop the monitor associated with ref.

!

[procedure] (! PID MSG)

Send msg to process pid.

!!

[procedure] (!! LIST MSG)

List must be a list of pids.

Send msg to all pids in list

?

[syntax] (? [TIMEOUT [DEFAULT]])

Fetch the first message from the mailbox.

??

[procedure] (?? PRED [TIMEOUT [DEFAULT]])

Fetch the next message that matches pred.

!?

[procedure] (!? PID MSG [TIMEOUT [DEFAULT]])

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)])

Match incoming messages against PAT ....

Each pattern must be a valid pattern for 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:

(use hardwood srfi-18)
(setup-thread)

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

Making a "server" process

(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

Selective message retrieval

(use hardwood srfi-18)
(setup-thread)

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

(?)                 --> 1
(?? odd?)           --> 3
(?)                 --> 2

RPC service

(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

Monitoring processes

(use hardwood srfi-18)
(setup-thread)

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

(define ref (monitor pid))

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

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
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