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# queue.tcl --
#
# Queue implementation for Tcl.
#
# Copyright (c) 1998-2000 by Scriptics Corporation.
# All rights reserved.
#
# RCS: @(#) $Id: queue.tcl,v 1.1 2000/02/05 03:20:20 ericm Exp $
namespace eval ::struct {}
namespace eval ::struct::queue {
# The queues array holds all of the queues you've made
variable queues
# counter is used to give a unique name for unnamed queues
variable counter 0
# commands is the list of subcommands recognized by the queue
variable commands [list \
"clear" \
"destroy" \
"get" \
"peek" \
"put" \
"size" \
]
# Only export one command, the one used to instantiate a new queue
namespace export queue
}
# ::struct::queue::queue --
#
# Create a new queue with a given name; if no name is given, use
# queueX, where X is a number.
#
# Arguments:
# name name of the queue; if null, generate one.
#
# Results:
# name name of the queue created
proc ::struct::queue::queue {{name ""}} {
variable queues
variable counter
if { [llength [info level 0]] == 1 } {
incr counter
set name "queue${counter}"
}
if { ![string equal [info commands ::$name] ""] } {
error "command \"$name\" already exists, unable to create queue"
}
# Initialize the queue as empty
set queues($name) [list ]
# Create the command to manipulate the queue
interp alias {} ::$name {} ::struct::queue::QueueProc $name
return $name
}
##########################
# Private functions follow
# ::struct::queue::QueueProc --
#
# Command that processes all queue object commands.
#
# Arguments:
# name name of the queue object to manipulate.
# args command name and args for the command
#
# Results:
# Varies based on command to perform
proc ::struct::queue::QueueProc {name {cmd ""} args} {
# Make sure this queue exists
if { ![info exists ::struct::queue::queues($name)] } {
error "unknown queue \"$name\""
}
# Do minimal args checks here
if { [llength [info level 0]] == 2 } {
error "wrong # args: should be \"$name option ?arg arg ...?\""
}
# Split the args into command and args components
if { [string equal [info commands ::struct::queue::_$cmd] ""] } {
variable commands
set optlist [join $commands ", "]
set optlist [linsert $optlist "end-1" "or"]
error "bad option \"$cmd\": must be $optlist"
}
return [uplevel 1 [list ::struct::queue::_$cmd $name] $args]
}
# ::struct::queue::_clear --
#
# Clear a queue.
#
# Arguments:
# name name of the queue object.
#
# Results:
# None.
proc ::struct::queue::_clear {name} {
variable queues
set queues($name) [list ]
return
}
# ::struct::queue::_destroy --
#
# Destroy a queue object by removing it's storage space and
# eliminating it's proc.
#
# Arguments:
# name name of the queue object.
#
# Results:
# None.
proc ::struct::queue::_destroy {name} {
variable queues
unset queues($name)
interp alias {} ::$name {}
return
}
# ::struct::queue::_get --
#
# Get an item from a queue.
#
# Arguments:
# name name of the queue object.
# count number of items to get; defaults to 1
#
# Results:
# item first count items from the queue; if there are not enough
# items in the queue, throws an error.
proc ::struct::queue::_get {name {count 1}} {
variable queues
if { $count < 1 } {
error "invalid item count $count"
}
if { $count > [llength $queues($name)] } {
error "insufficient items in queue to fill request"
}
if { $count == 1 } {
# Handle this as a special case, so single item gets aren't listified
set item [lindex $queues($name) 0]
set queues($name) [lreplace $queues($name) 0 0]
return $item
}
# Otherwise, return a list of items
set index [expr {$count - 1}]
set result [lrange $queues($name) 0 $index]
set queues($name) [lreplace $queues($name) 0 $index]
return $result
}
# ::struct::queue::_peek --
#
# Retrive the value of an item on the queue without removing it.
#
# Arguments:
# name name of the queue object.
# count number of items to peek; defaults to 1
#
# Results:
# items top count items from the queue; if there are not enough items
# to fufill the request, throws an error.
proc ::struct::queue::_peek {name {count 1}} {
variable queues
if { $count < 1 } {
error "invalid item count $count"
}
if { $count > [llength $queues($name)] } {
error "insufficient items in queue to fill request"
}
if { $count == 1 } {
# Handle this as a special case, so single item pops aren't listified
return [lindex $queues($name) 0]
}
# Otherwise, return a list of items
set index [expr {$count - 1}]
return [lrange $queues($name) 0 $index]
}
# ::struct::queue::_put --
#
# Put an item into a queue.
#
# Arguments:
# name name of the queue object
# args items to put.
#
# Results:
# None.
proc ::struct::queue::_put {name args} {
variable queues
if { [llength $args] == 0 } {
error "wrong # args: should be \"$name put item ?item ...?\""
}
foreach item $args {
lappend queues($name) $item
}
return
}
# ::struct::queue::_size --
#
# Return the number of objects on a queue.
#
# Arguments:
# name name of the queue object.
#
# Results:
# count number of items on the queue.
proc ::struct::queue::_size {name} {
variable queues
return [llength $queues($name)]
}
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