[suggestion+code] timed deq for the Queue class?

[Andrew S. Townley]

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Hi,

Based on my earlier emails and further thinking, I've implemented the
following methods which seem to work and which other people might find
useful. No guarantees that they're 100% correct, but it seems to do
what I want. Would it be possible to add something like this to the
standard Queue?

$ cat fu.rb
require 'thread'
require 'timeout'

class TimedReadQueue < Queue

# Waits for the specified timeout (seconds) and returns,
# waking up the accessing thread. This method avoids a
# problem with using Timeout and Queue together to achieve
# the same result.

def tdeq(timeout)
data = nil

if(empty?)
mt = Thread.current

# This thread will wait for the timeout. If it is still
# alive, it will remove the read thread (rt) from the
# waiting list, kill it and restart the main thread.

rt = nil
tt = Thread.new do
Thread.stop; sleep(timeout); @waiting.delete(rt); mt.wakeup
__timeout
end

# This thread will actually try and read the data. If
# it gets data, it will kill the timer and wake up the
# main thread.

rt = Thread.new do
Thread.stop; data = deq; __arnold(tt); mt.wakeup
__read
end

begin
tt.run
rt.run
Thread.stop
ensure
mt.wakeup
__arnold(tt)
__arnold(rt)
end
else
# just read the data
begin
data = deq(true)
rescue ThreadError
# don't care
data = nil
end
end

# return the data value
data
end

private

# This method takes a thread and unconditionally terminates
# it, completely and utterly

def __arnold(thread)
thread.kill if thread && thread.alive?
end

def __timeout
puts("TIMEOUT: #{length} elements; #{num_waiting} threads waiting.")
end

def __read
puts("READ: #{length} elements; #{num_waiting} threads waiting.")
end
end

The entire program (with minimal, manual tests) is also attached.

Any/all feedback more than welcome.

Cheers,

ast


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