bt-semaphore

A simple semaphore class for bordeaux-threads inspired by SBCL's semaphore.

Obsolete! bordeaux-threads has its own built-in semaphores since version 0.8.6, so you should definitely use that instead of bt-semaphore.

Installation

bt-semaphore is available via Quicklisp. You can also clone the Git repo if you're curious:

cd ~/quicklisp/local-projects
git clone https://github.com/rmoritz/bt-semaphore

Usage

There are seven functions of interest at the moment:

• make-semaphore creates a semaphore instance
• wait-on-semaphore blocks until the semaphore can be decremented (ie. its count > 0) or the timeout has expired
• signal-semaphore increments the semaphore & wakes n waiting threads
• try-semaphore decrements the semaphore without blocking
• semaphore-count returns the current count of the semaphore
• semaphore-waiters returns the number of threads waiting on semaphore
• semaphore-name is an accessor for the semaphore's name slot

To illustrate, here's a tiny example:

(ql:quickload :bt-semaphore)

(defun semaphore-demo ()
  (defparameter sem (bt-sem:make-semaphore))
  (defparameter lock (bt:make-lock))
  (defparameter num 0)
  
  (format t "spawn 20 threads with 4s timeout~%")
  (loop
    repeat 20
    do (bt:make-thread
         (lambda ()
           (if (bt-sem:wait-on-semaphore sem :timeout 4)
             (bt:with-lock-held (lock)
               (incf num))))))
  (format t "num is ~d~%" num)
  (sleep 0.33)
  (format t "there are ~d waiting threads~%~%" (bt-sem:semaphore-waiters sem))

  (format t "signal 5 threads~%")
  (bt-sem:signal-semaphore sem 5)
  (sleep 0.33)
  (bt:with-lock-held (lock)
    (format t "num is ~d~%" num))
  (format t "there are ~d waiting threads~%~%" (bt-sem:semaphore-waiters sem))

  (format t "signal 10 threads~%")
  (bt-sem:signal-semaphore sem 10)
  (sleep 0.33)
  (bt:with-lock-held (lock)
    (format t "num is ~d~%" num))
  (format t "there are ~d waiting threads~%~%" (bt-sem:semaphore-waiters sem))

  (format t "4s sleep~%")
  (sleep 4)
  (bt:with-lock-held (lock)
    (format t "num is ~d~%" num))
  (format t "there are ~d waiting threads~%~%" (bt-sem:semaphore-waiters sem)))

Calling SEMAPHORE-DEMO at the REPL should produce the following output:

spawn 20 threads with 4s timeout
num is 0
there are 20 waiting threads

signal 5 threads
num is 5
there are 15 waiting threads

signal 10 threads
num is 15
there are 5 waiting threads

4s sleep
num is 15
there are 0 waiting threads

Status

Working, but obsolete: bordeaux-threads has semaphore support since version 0.8.6. You should definitely be using that instead of bt-semaphore.

You can run the test suites to verify that everything is working as it should by invoking (ql:quickload :bt-semaphore-test) or (asdf:test-system :bt-semaphore).

Bugs

Found one? Report it here, thanks.

Author

• Ralph Moeritz (ralphmoritz@outlook.com)

License

Copyright (c) Ralph Moeritz 2013.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.