I've got a device I'm talking to and when there are otherwise no interesting commands to send, the "status_poll" command is sent. The device takes a little while to respond, in which time a lot of stuff can happen, namely the queuing of more commands. I tried a simpler approach on my first iteration where I'd just return the default when the list was empty (not using the queue to also manage the default), but I ended up losing commands in the case where I'd sent a default message and queued a new command before the response to the default. You see, pop gets called on response, so this freshly queued command was popped before it ever had a chance to be sent.
Other: been playing with dropping .tm files into common area for easy package require (queue_with_default-0.0.1.tm), also first go at TclOO
package provide queue_with_default 0.0.1
package require TclOO
oo::class create queue_with_default {
variable _queue _default _default_in_queue _default_seen
constructor {default} {
set _queue [list]
set _default $default
set _default_in_queue no
set _default_seen no
my pop
return
}
method push {message} {
lappend _queue $message
if {$_default_in_queue && !$_default_seen} {
my pop
}
return
}
method peek {} {
if {$_default_in_queue} {
set _default_seen yes
}
lindex $_queue 0
}
method pop {} {
set _queue [lrange $_queue 1 end]
set _default_in_queue no
set _default_seen no
if {[llength $_queue] == 0} {
my push $_default
set _default_in_queue yes
set _default_seen no
}
return
}
}
And the client code:
queue_with_default create commands status_poll
commands peek; #the default has been seen
commands push reset
commands peek; #still looking at default
commands pop
commands peek; #now we see the reset
commands pop
#queue is "empty" here, unseen default at the front
commands push reset
commands peek; #this time we see reset because the default was never seen
commands pop
Any doubts welcome.
