| '\" |
| '\" Copyright (c) 1990 The Regents of the University of California. |
| '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. |
| '\" |
| '\" See the file "license.terms" for information on usage and redistribution |
| '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
| '\" |
| '\" RCS: @(#) $Id: Preserve.3,v 1.4 2002/02/26 02:22:20 hobbs Exp $ |
| '\" |
| '\" The 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 |
| '\" Start of list of standard options for a Tk widget. The |
| '\" options follow on successive lines, in four 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. |
| '\" |
| '\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $ |
| '\" |
| '\" # 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 |
| .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 \\fBoptions\\fR 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 |
| .. |
| .de UL |
| \\$1\l'|0\(ul'\\$2 |
| .. |
| .TH Tcl_Preserve 3 7.5 Tcl "Tcl Library Procedures" |
| .BS |
| .SH NAME |
| Tcl_Preserve, Tcl_Release, Tcl_EventuallyFree \- avoid freeing storage while it's being used |
| .SH SYNOPSIS |
| .nf |
| \fB#include <tcl.h>\fR |
| .sp |
| \fBTcl_Preserve\fR(\fIclientData\fR) |
| .sp |
| \fBTcl_Release\fR(\fIclientData\fR) |
| .sp |
| \fBTcl_EventuallyFree\fR(\fIclientData, freeProc\fR) |
| .SH ARGUMENTS |
| .AS Tcl_FreeProc clientData |
| .AP ClientData clientData in |
| Token describing structure to be freed or reallocated. Usually a pointer |
| to memory for structure. |
| .AP Tcl_FreeProc *freeProc in |
| Procedure to invoke to free \fIclientData\fR. |
| .BE |
| |
| .SH DESCRIPTION |
| .PP |
| These three procedures help implement a simple reference count mechanism |
| for managing storage. They are designed to solve a problem |
| having to do with widget deletion, but are also useful in many other |
| situations. When a widget is deleted, its |
| widget record (the structure holding information specific to the |
| widget) must be returned to the storage allocator. |
| However, it's possible that the widget record is in active use |
| by one of the procedures on the stack at the time of the deletion. |
| This can happen, for example, if the command associated with a button |
| widget causes the button to be destroyed: an X event causes an |
| event-handling C procedure in the button to be invoked, which in |
| turn causes the button's associated Tcl command to be executed, |
| which in turn causes the button to be deleted, which in turn causes |
| the button's widget record to be de-allocated. |
| Unfortunately, when the Tcl command returns, the button's |
| event-handling procedure will need to reference the |
| button's widget record. |
| Because of this, the widget record must not be freed as part of the |
| deletion, but must be retained until the event-handling procedure has |
| finished with it. |
| In other situations where the widget is deleted, it may be possible |
| to free the widget record immediately. |
| .PP |
| \fBTcl_Preserve\fR and \fBTcl_Release\fR |
| implement short-term reference counts for their \fIclientData\fR |
| argument. |
| The \fIclientData\fR argument identifies an object and usually |
| consists of the address of a structure. |
| The reference counts guarantee that an object will not be freed |
| until each call to \fBTcl_Preserve\fR for the object has been |
| matched by calls to \fBTcl_Release\fR. |
| There may be any number of unmatched \fBTcl_Preserve\fR calls |
| in effect at once. |
| .PP |
| \fBTcl_EventuallyFree\fR is invoked to free up its \fIclientData\fR |
| argument. |
| It checks to see if there are unmatched \fBTcl_Preserve\fR calls |
| for the object. |
| If not, then \fBTcl_EventuallyFree\fR calls \fIfreeProc\fR immediately. |
| Otherwise \fBTcl_EventuallyFree\fR records the fact that \fIclientData\fR |
| needs eventually to be freed. |
| When all calls to \fBTcl_Preserve\fR have been matched with |
| calls to \fBTcl_Release\fR then \fIfreeProc\fR will be called by |
| \fBTcl_Release\fR to do the cleanup. |
| .PP |
| All the work of freeing the object is carried out by \fIfreeProc\fR. |
| \fIFreeProc\fR must have arguments and result that match the |
| type \fBTcl_FreeProc\fR: |
| .CS |
| typedef void Tcl_FreeProc(char *\fIblockPtr\fR); |
| .CE |
| The \fIblockPtr\fR argument to \fIfreeProc\fR will be the |
| same as the \fIclientData\fR argument to \fBTcl_EventuallyFree\fR. |
| The type of \fIblockPtr\fR (\fBchar *\fR) is different than the type of the |
| \fIclientData\fR argument to \fBTcl_EventuallyFree\fR for historical |
| reasons, but the value is the same. |
| .PP |
| When the \fIclientData\fR argument to \fBTcl_EventuallyFree\fR |
| refers to storage allocated and returned by a prior call to |
| \fBTcl_Alloc\fR, \fBckalloc\fR, or another function of the Tcl library, |
| then the \fIfreeProc\fR argument should be given the special value of |
| \fBTCL_DYNAMIC\fR. |
| .PP |
| This mechanism can be used to solve the problem described above |
| by placing \fBTcl_Preserve\fR and \fBTcl_Release\fR calls around |
| actions that may cause undesired storage re-allocation. The |
| mechanism is intended only for short-term use (i.e. while procedures |
| are pending on the stack); it will not work efficiently as a |
| mechanism for long-term reference counts. |
| The implementation does not depend in any way on the internal |
| structure of the objects being freed; it keeps the reference |
| counts in a separate structure. |
| |
| .SH "SEE ALSO" |
| Tcl_Interp, Tcl_Alloc |
| |
| .SH KEYWORDS |
| free, reference count, storage |