'\" '\" Generated from file 'pool\&.man' by tcllib/doctools with format 'nroff' '\" Copyright (c) 2002, Erik Leunissen '\" .TH "struct::pool" 3tcl 1\&.2\&.3 tcllib "Tcl Data Structures" .\" The -*- nroff -*- definitions below are for supplemental macros used .\" in Tcl/Tk manual entries. .\" .\" .AP type name in/out ?indent? .\" Start paragraph describing an argument to a library procedure. .\" type is type of argument (int, etc.), in/out is either "in", "out", .\" or "in/out" to describe whether procedure reads or modifies arg, .\" and indent is equivalent to second arg of .IP (shouldn't ever be .\" needed; use .AS below instead) .\" .\" .AS ?type? ?name? .\" Give maximum sizes of arguments for setting tab stops. Type and .\" name are examples of largest possible arguments that will be passed .\" to .AP later. If args are omitted, default tab stops are used. .\" .\" .BS .\" Start box enclosure. From here until next .BE, everything will be .\" enclosed in one large box. .\" .\" .BE .\" End of box enclosure. .\" .\" .CS .\" Begin code excerpt. .\" .\" .CE .\" End code excerpt. .\" .\" .VS ?version? ?br? .\" Begin vertical sidebar, for use in marking newly-changed parts .\" of man pages. The first argument is ignored and used for recording .\" the version when the .VS was added, so that the sidebars can be .\" found and removed when they reach a certain age. If another argument .\" is present, then a line break is forced before starting the sidebar. .\" .\" .VE .\" End of vertical sidebar. .\" .\" .DS .\" Begin an indented unfilled display. .\" .\" .DE .\" End of indented unfilled display. .\" .\" .SO ?manpage? .\" Start of list of standard options for a Tk widget. The manpage .\" argument defines where to look up the standard options; if .\" omitted, defaults to "options". The options follow on successive .\" lines, in three columns separated by tabs. .\" .\" .SE .\" End of list of standard options for a Tk widget. .\" .\" .OP cmdName dbName dbClass .\" Start of description of a specific option. cmdName gives the .\" option's name as specified in the class command, dbName gives .\" the option's name in the option database, and dbClass gives .\" the option's class in the option database. .\" .\" .UL arg1 arg2 .\" Print arg1 underlined, then print arg2 normally. .\" .\" .QW arg1 ?arg2? .\" Print arg1 in quotes, then arg2 normally (for trailing punctuation). .\" .\" .PQ arg1 ?arg2? .\" Print an open parenthesis, arg1 in quotes, then arg2 normally .\" (for trailing punctuation) and then a closing parenthesis. .\" .\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. .if t .wh -1.3i ^B .nr ^l \n(.l .ad b .\" # Start an argument description .de AP .ie !"\\$4"" .TP \\$4 .el \{\ . ie !"\\$2"" .TP \\n()Cu . el .TP 15 .\} .ta \\n()Au \\n()Bu .ie !"\\$3"" \{\ \&\\$1 \\fI\\$2\\fP (\\$3) .\".b .\} .el \{\ .br .ie !"\\$2"" \{\ \&\\$1 \\fI\\$2\\fP .\} .el \{\ \&\\fI\\$1\\fP .\} .\} .. .\" # define tabbing values for .AP .de AS .nr )A 10n .if !"\\$1"" .nr )A \\w'\\$1'u+3n .nr )B \\n()Au+15n .\" .if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n .nr )C \\n()Bu+\\w'(in/out)'u+2n .. .AS Tcl_Interp Tcl_CreateInterp in/out .\" # BS - start boxed text .\" # ^y = starting y location .\" # ^b = 1 .de BS .br .mk ^y .nr ^b 1u .if n .nf .if n .ti 0 .if n \l'\\n(.lu\(ul' .if n .fi .. .\" # BE - end boxed text (draw box now) .de BE .nf .ti 0 .mk ^t .ie n \l'\\n(^lu\(ul' .el \{\ .\" Draw four-sided box normally, but don't draw top of .\" box if the box started on an earlier page. .ie !\\n(^b-1 \{\ \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' .\} .el \}\ \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' .\} .\} .fi .br .nr ^b 0 .. .\" # VS - start vertical sidebar .\" # ^Y = starting y location .\" # ^v = 1 (for troff; for nroff this doesn't matter) .de VS .if !"\\$2"" .br .mk ^Y .ie n 'mc \s12\(br\s0 .el .nr ^v 1u .. .\" # VE - end of vertical sidebar .de VE .ie n 'mc .el \{\ .ev 2 .nf .ti 0 .mk ^t \h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n' .sp -1 .fi .ev .\} .nr ^v 0 .. .\" # Special macro to handle page bottom: finish off current .\" # box/sidebar if in box/sidebar mode, then invoked standard .\" # page bottom macro. .de ^B .ev 2 'ti 0 'nf .mk ^t .if \\n(^b \{\ .\" Draw three-sided box if this is the box's first page, .\" draw two sides but no top otherwise. .ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c .el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c .\} .if \\n(^v \{\ .nr ^x \\n(^tu+1v-\\n(^Yu \kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c .\} .bp 'fi .ev .if \\n(^b \{\ .mk ^y .nr ^b 2 .\} .if \\n(^v \{\ .mk ^Y .\} .. .\" # DS - begin display .de DS .RS .nf .sp .. .\" # DE - end display .de DE .fi .RE .sp .. .\" # SO - start of list of standard options .de SO 'ie '\\$1'' .ds So \\fBoptions\\fR 'el .ds So \\fB\\$1\\fR .SH "STANDARD OPTIONS" .LP .nf .ta 5.5c 11c .ft B .. .\" # SE - end of list of standard options .de SE .fi .ft R .LP See the \\*(So manual entry for details on the standard options. .. .\" # OP - start of full description for a single option .de OP .LP .nf .ta 4c Command-Line Name: \\fB\\$1\\fR Database Name: \\fB\\$2\\fR Database Class: \\fB\\$3\\fR .fi .IP .. .\" # CS - begin code excerpt .de CS .RS .nf .ta .25i .5i .75i 1i .. .\" # CE - end code excerpt .de CE .fi .RE .. .\" # UL - underline word .de UL \\$1\l'|0\(ul'\\$2 .. .\" # QW - apply quotation marks to word .de QW .ie '\\*(lq'"' ``\\$1''\\$2 .\"" fix emacs highlighting .el \\*(lq\\$1\\*(rq\\$2 .. .\" # PQ - apply parens and quotation marks to word .de PQ .ie '\\*(lq'"' (``\\$1''\\$2)\\$3 .\"" fix emacs highlighting .el (\\*(lq\\$1\\*(rq\\$2)\\$3 .. .\" # QR - quoted range .de QR .ie '\\*(lq'"' ``\\$1''\\-``\\$2''\\$3 .\"" fix emacs highlighting .el \\*(lq\\$1\\*(rq\\-\\*(lq\\$2\\*(rq\\$3 .. .\" # MT - "empty" string .de MT .QW "" .. .BS .SH NAME struct::pool \- Create and manipulate pool objects (of discrete items) .SH SYNOPSIS package require \fBTcl 8\&.2\fR .sp package require \fBstruct::pool ?1\&.2\&.3?\fR .sp \fB::struct::pool\fR ?\fIpoolName\fR? ?\fImaxsize\fR? .sp \fBpoolName\fR \fIoption\fR ?\fIarg arg \&.\&.\&.\fR? .sp \fIpoolName\fR \fBadd\fR \fIitemName1\fR ?\fIitemName2 itemName3 \&.\&.\&.\fR? .sp \fIpoolName\fR \fBclear\fR ?\fB-force\fR? .sp \fIpoolName\fR \fBdestroy\fR ?\fB-force\fR? .sp \fIpoolName\fR \fBinfo\fR \fItype\fR ?\fIarg\fR? .sp \fIpoolName\fR \fBmaxsize\fR ?\fImaxsize\fR? .sp \fIpoolName\fR \fBrelease\fR \fIitemName\fR .sp \fIpoolName\fR \fBremove\fR \fIitemName\fR ?\fB-force\fR? .sp \fIpoolName\fR \fBrequest\fR itemVar ?options? .sp .BE .SH DESCRIPTION .PP This package provides pool objects which can be used to manage finite collections of discrete items\&. .TP \fB::struct::pool\fR ?\fIpoolName\fR? ?\fImaxsize\fR? Creates a new pool object\&. If no \fIpoolName\fR is supplied, then the new pool will be named pool\fBX\fR, where X is a positive integer\&. The optional second argument \fImaxsize\fR has to be a positive integer indicating the maximum size of the pool; this is the maximum number of items the pool may hold\&. The default for this value is \fB10\fR\&. .sp The pool object has an associated global Tcl command whose name is \fIpoolName\fR\&. This command may be used to invoke various configuration operations on the report\&. It has the following general form: .RS .TP \fBpoolName\fR \fIoption\fR ?\fIarg arg \&.\&.\&.\fR? \fIOption\fR and the \fIarg\fRs determine the exact behavior of the command\&. See section \fBPOOL OBJECT COMMAND\fR for a detailed list of options and their behaviour\&. .RE .PP .PP .SH "POOLS AND ALLOCATION" The purpose of the pool command and the pool object command that it generates, is to manage pools of discrete items\&. Examples of a pool of discrete items are: .IP \(bu the seats in a cinema, theatre, train etc\&.\&. for which visitors/travelers can make a reservation; .IP \(bu the dynamic IP-addresses that an ISP can dole out to subscribers; .IP \(bu a car rental's collection of cars, which can be rented by customers; .IP \(bu the class rooms in a school building, which need to be scheduled; .IP \(bu the database connections available to client-threads in a web-server application; .IP \(bu the books in a library that customers can borrow; .IP \(bu etc \&.\&.\&. .PP .PP The common denominator in the examples is that there is a more or less fixed number of items (seats, IP-addresses, cars, \&.\&.\&.) that are supposed to be allocated on a more or less regular basis\&. An item can be allocated only once at a time\&. An item that is allocated, must be released before it can be re-allocated\&. While several items in a pool are being allocated and released continuously, the total number of items in the pool remains constant\&. .PP Keeping track of which items are allocated, and by whom, is the purpose of the pool command and its subordinates\&. .PP \fIPool parlance\fR: If we say that an item is \fIallocated\fR, it means that the item is \fIbusy\fR, \fIowned\fR or \fIoccupied\fR; it is not available anymore\&. If an item is \fIfree\fR, it is \fIavailable\fR\&. Deallocating an item is equivalent to setting free or releasing an item\&. The person or entity to which the item has been allotted is said to own the item\&. .SH ITEMS \fIDiscrete items\fR .PP The \fBpool\fR command is designed for \fIdiscrete items only\fR\&. Note that there are pools where allocation occurs on a non-discrete basis, for example computer memory\&. There are also pools from which the shares that are doled out are not expected to be returned, for example a charity fund or a pan of soup from which you may receive a portion\&. Finally, there are even pools from which nothing is ever allocated or returned, like a swimming pool or a cesspool\&. .PP \fIUnique item names\fR .PP A pool cannot manage duplicate item names\&. Therefore, items in a pool must have unique names\&. .PP \fIItem equivalence\fR .PP From the point of view of the manager of a pool, items are equivalent\&. The manager of a pool is indifferent about which entity/person occupies a given item\&. However, clients may have preferences for a particular item, based on some item property they know\&. .PP \fIPreferences\fR .PP A future owner may have a preference for a particular item\&. Preference based allocation is supported (see the \fB-prefer\fR option to the request subcommand)\&. A preference for a particular item is most likely to result from variability among features associated with the items\&. Note that the pool commands themselves are not designed to manage such item properties\&. If item properties play a role in an application, they should be managed separately\&. .SH "POOL OBJECT COMMAND" The following subcommands and corresponding arguments are available to any pool object command\&. .TP \fIpoolName\fR \fBadd\fR \fIitemName1\fR ?\fIitemName2 itemName3 \&.\&.\&.\fR? This command adds the items on the command line to the pool\&. If duplicate item names occur on the command line, an error is raised\&. If one or more of the items already exist in the pool, this also is considered an error\&. .TP \fIpoolName\fR \fBclear\fR ?\fB-force\fR? Removes all items from the pool\&. If there are any allocated items at the time when the command is invoked, an error is raised\&. This behaviour may be modified through the \fB-force\fR argument\&. If it is supplied on the command line, the pool will be cleared regardless the allocation state of its items\&. .TP \fIpoolName\fR \fBdestroy\fR ?\fB-force\fR? Destroys the pool data structure, all associated variables and the associated pool object command\&. By default, the command checks whether any items are still allocated and raises an error if such is the case\&. This behaviour may be modified through the argument \fB-force\fR\&. If it is supplied on the command line, the pool data structure will be destroyed regardless allocation state of its items\&. .TP \fIpoolName\fR \fBinfo\fR \fItype\fR ?\fIarg\fR? Returns various information about the pool for further programmatic use\&. The \fItype\fR argument indicates the type of information requested\&. Only the type \fBallocID\fR uses an additional argument\&. .RS .TP \fBallocID\fR \fIitemName\fR returns the allocID of the item whose name is \fIitemName\fR\&. Free items have an allocation id of \fB-1\fR\&. .TP \fBallitems\fR returns a list of all items in the pool\&. .TP \fBallocstate\fR Returns a list of key-value pairs, where the keys are the items and the values are the corresponding allocation id's\&. Free items have an allocation id of \fB-1\fR\&. .TP \fBcursize\fR returns the current pool size, i\&.e\&. the number of items in the pool\&. .TP \fBfreeitems\fR returns a list of items that currently are not allocated\&. .TP \fBmaxsize\fR returns the maximum size of the pool\&. .RE .sp .TP \fIpoolName\fR \fBmaxsize\fR ?\fImaxsize\fR? Sets or queries the maximum size of the pool, depending on whether the \fImaxsize\fR argument is supplied or not\&. If \fImaxsize\fR is supplied, the maximum size of the pool will be set to that value\&. If no argument is supplied, the current maximum size of the pool is returned\&. In this variant, the command is an alias for: .sp \fBpoolName info maxsize\fR\&. .sp The \fImaxsize\fR argument has to be a positive integer\&. .TP \fIpoolName\fR \fBrelease\fR \fIitemName\fR Releases the item whose name is \fIitemName\fR that was allocated previously\&. An error is raised if the item was not allocated at the time when the command was issued\&. .TP \fIpoolName\fR \fBremove\fR \fIitemName\fR ?\fB-force\fR? Removes the item whose name is \fIitemName\fR from the pool\&. If the item was allocated at the time when the command was invoked, an error is raised\&. This behaviour may be modified through the optional argument \fB-force\fR\&. If it is supplied on the command line, the item will be removed regardless its allocation state\&. .TP \fIpoolName\fR \fBrequest\fR itemVar ?options? Handles a request for an item, taking into account a possible preference for a particular item\&. There are two possible outcomes depending on the availability of items: .RS .IP [1] The request is honoured, an item is allocated and the variable whose name is passed with the argument \fIitemVar\fR will be set to the name of the item that was allocated\&. The command returns 1\&. .IP [2] The request is denied\&. No item is allocated\&. The variable whose name is itemVar is not set\&. Attempts to read \fIitemVar\fR may raise an error if the variable was not defined before issuing the request\&. The command returns 0\&. .RE .sp The return values from this command are meant to be inspected\&. The examples below show how to do this\&. Failure to check the return value may result in erroneous behaviour\&. If no preference for a particular item is supplied through the option \fB-prefer\fR (see below), then all requests are honoured as long as items are available\&. .sp The following options are supported: .RS .TP \fB-allocID\fR \fIallocID\fR If the request is honoured, an item will be allocated to the entity identified by allocID\&. If the allocation state of an item is queried, it is this allocation ID that will be returned\&. If the option \fB-allocID\fR is not supplied, the item will be given to and owned by \fBdummyID\fR\&. Allocation id's may be anything except the value -1, which is reserved for free items\&. .TP \fB-prefer\fR \fIpreferredItem\fR This option modifies the allocation strategy as follows: If the item whose name is \fIpreferredItem\fR is not allocated at the time when the command is invoked, the request is honoured (return value is 1)\&. If the item was allocated at the time when the command was invoked, the request is denied (return value is 0)\&. .RE .PP .SH EXAMPLES Two examples are provided\&. The first one mimics a step by step interactive tclsh session, where each step is explained\&. The second example shows the usage in a server application that talks to a back-end application\&. .PP \fIExample 1\fR .PP This example presents an interactive tclsh session which considers the case of a Car rental's collection of cars\&. Ten steps explain its usage in chronological order, from the creation of the pool, via the most important stages in the usage of a pool, to the final destruction\&. .PP \fINote aside:\fR .PP In this example, brand names are used to label the various items\&. However, a brand name could be regarded as a property of an item\&. Because the pool command is not designed to manage properties of items, they need to be managed separately\&. In the latter case the items should be labeled with more neutral names such as: car1, car2, car3 , etc \&.\&.\&. and a separate database or array should hold the brand names associated with the car labels\&. .PP .CS 1\&. Load the package into an interpreter % package require pool 0\&.1 2\&. Create a pool object called `CarPool' with a maximum size of 55 items (cars): % pool CarPool 55 CarPool 4\&. Add items to the pool: % CarPool add Toyota Trabant Chrysler1 Chrysler2 Volkswagen 5\&. Somebody crashed the Toyota\&. Remove it from the pool as follows: % CarPool remove Toyota 6\&. Acquired a new car for the pool\&. Add it as follows: % CarPool add Nissan 7\&. Check whether the pool was adjusted correctly: % CarPool info allitems Trabant Chrysler1 Chrysler2 Volkswagen Nissan .CE .PP Suspend the interactive session temporarily, and show the programmatic use of the request subcommand: .PP .CS # Mrs\&. Swift needs a car\&. She doesn't have a preference for a # particular car\&. We'll issue a request on her behalf as follows: if { [CarPool request car -allocID "Mrs\&. Swift"] } { # request was honoured, process the variable `car' puts "$car has been allocated to [CarPool info allocID $car]\&." } else { # request was denied puts "No car available\&." } .CE .PP Note how the \fBif\fR command uses the value returned by the \fBrequest\fR subcommand\&. .PP .CS # Suppose Mr\&. Wiggly has a preference for the Trabant: if { [CarPool request car -allocID "Mr\&. Wiggly" -prefer Trabant] } { # request was honoured, process the variable `car' puts "$car has been allocated to [CarPool info allocID $car]\&." } else { # request was denied puts "The Trabant was not available\&." } .CE .PP Resume the interactive session: .PP .CS 8\&. When the car is returned then you can render it available by: % CarPool release Trabant 9\&. When done, you delete the pool\&. % CarPool destroy Couldn't destroy `CarPool' because some items are still allocated\&. Oops, forgot that Mrs\&. Swift still occupies a car\&. 10\&. We force the destruction of the pool as follows: % CarPool destroy -force .CE .PP \fIExample 2\fR .PP This example describes the case from which the author's need for pool management originated\&. It is an example of a server application that receives requests from client applications\&. The client requests are dispatched onto a back-end application before being returned to the client application\&. In many cases there are a few equivalent instances of back-end applications to which a client request may be passed along\&. The file descriptors that identify the channels to these back-end instances make up a pool of connections\&. A particular connection may be allocated to just one client request at a time\&. .PP .CS # Create the pool of connections (pipes) set maxpipes 10 pool Pipes $maxpipes for {set i 0} {$i < $maxpipes} {incr i} { set fd [open "|backendApplication" w+] Pipes add $fd } # A client request comes in\&. The request is identified as `clientX'\&. # Dispatch it onto an instance of a back-end application if { [Pipes request fd -allocID clientX] } { # a connection was allocated # communicate to the back-end application via the variable `fd' puts $fd "someInstruction" # \&.\&.\&.\&.\&.\&. etc\&. } else { # all connections are currently occupied # store the client request in a queue for later processing, # or return a 'Server busy' message to the client\&. } .CE .SH "BUGS, IDEAS, FEEDBACK" This document, and the package it describes, will undoubtedly contain bugs and other problems\&. Please report such in the category \fIstruct :: pool\fR of the \fITcllib Trackers\fR [http://core\&.tcl\&.tk/tcllib/reportlist]\&. Please also report any ideas for enhancements you may have for either package and/or documentation\&. .PP When proposing code changes, please provide \fIunified diffs\fR, i\&.e the output of \fBdiff -u\fR\&. .PP Note further that \fIattachments\fR are strongly preferred over inlined patches\&. Attachments can be made by going to the \fBEdit\fR form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar\&. .SH KEYWORDS discrete items, finite, pool, struct .SH CATEGORY Data structures .SH COPYRIGHT .nf Copyright (c) 2002, Erik Leunissen .fi