man/man3/Tcl_Preserve.3 - toolchains/skids - Git at Google

 '\"
 '\" 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.
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 '\"	Begin vertical sidebar, for use in marking newly-changed parts
 '\"	of man pages.  The first argument is ignored and used for recording
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 '\"	End of vertical sidebar.
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 '\"	Begin an indented unfilled display.
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 '\" .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
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 .if n .fi
 ..
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 .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
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 .sp -1
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 .\}
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 .\"	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
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 .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
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 .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
	'\"
	'\" 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