[OpenSPARC-T2-SAM] / sam-t2 / devtools / v9 / man / man3 / Tcl_Preserve.3

'\"
'\" 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
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'\" 
'\" 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
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'\"	options follow on successive lines, in four columns separated
'\"	by tabs.
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'\" .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.
'\"
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'\"	Print arg1 underlined, then print arg2 normally.
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'\"
'\"	# Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
.if t .wh -1.3i ^B
.nr ^l \n(.l
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.ie !"\\$4"" .TP \\$4
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.AS Tcl_Interp Tcl_CreateInterp in/out
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\h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
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.LP
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.LP
See the \\fBoptions\\fR manual entry for details on the standard options.
..
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.LP
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Command-Line Name:	\\fB\\$1\\fR
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.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
Commit	Line	Data
920dae64 AT	1	'\"
	2	'\" Copyright (c) 1990 The Regents of the University of California.
	3	'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
	4	'\"
	5	'\" See the file "license.terms" for information on usage and redistribution
	6	'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
	7	'\"
	8	'\" RCS: @(#) $Id: Preserve.3,v 1.4 2002/02/26 02:22:20 hobbs Exp $
	9	'\"
	10	'\" The definitions below are for supplemental macros used in Tcl/Tk
	11	'\" manual entries.
	12	'\"
	13	'\" .AP type name in/out ?indent?
	14	'\" Start paragraph describing an argument to a library procedure.
	15	'\" type is type of argument (int, etc.), in/out is either "in", "out",
	16	'\" or "in/out" to describe whether procedure reads or modifies arg,
	17	'\" and indent is equivalent to second arg of .IP (shouldn't ever be
	18	'\" needed; use .AS below instead)
	19	'\"
	20	'\" .AS ?type? ?name?
	21	'\" Give maximum sizes of arguments for setting tab stops. Type and
	22	'\" name are examples of largest possible arguments that will be passed
	23	'\" to .AP later. If args are omitted, default tab stops are used.
	24	'\"
	25	'\" .BS
	26	'\" Start box enclosure. From here until next .BE, everything will be
	27	'\" enclosed in one large box.
	28	'\"
	29	'\" .BE
	30	'\" End of box enclosure.
	31	'\"
	32	'\" .CS
	33	'\" Begin code excerpt.
	34	'\"
	35	'\" .CE
	36	'\" End code excerpt.
	37	'\"
	38	'\" .VS ?version? ?br?
	39	'\" Begin vertical sidebar, for use in marking newly-changed parts
	40	'\" of man pages. The first argument is ignored and used for recording
	41	'\" the version when the .VS was added, so that the sidebars can be
	42	'\" found and removed when they reach a certain age. If another argument
	43	'\" is present, then a line break is forced before starting the sidebar.
	44	'\"
	45	'\" .VE
	46	'\" End of vertical sidebar.
	47	'\"
	48	'\" .DS
	49	'\" Begin an indented unfilled display.
	50	'\"
	51	'\" .DE
	52	'\" End of indented unfilled display.
	53	'\"
	54	'\" .SO
	55	'\" Start of list of standard options for a Tk widget. The
	56	'\" options follow on successive lines, in four columns separated
	57	'\" by tabs.
	58	'\"
	59	'\" .SE
	60	'\" End of list of standard options for a Tk widget.
	61	'\"
	62	'\" .OP cmdName dbName dbClass
	63	'\" Start of description of a specific option. cmdName gives the
	64	'\" option's name as specified in the class command, dbName gives
65	'\" the option's name in the option database, and dbClass gives
66	'\" the option's class in the option database.
67	'\"
68	'\" .UL arg1 arg2
69	'\" Print arg1 underlined, then print arg2 normally.
70	'\"
71	'\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $
72	'\"
73	'\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
74	.if t .wh -1.3i ^B
75	.nr ^l \n(.l
76	.ad b
77	'\" # Start an argument description
78	.de AP
79	.ie !"\\$4"" .TP \\$4
80	.el \{\
81	. ie !"\\$2"" .TP \\n()Cu
82	. el .TP 15
83	.\}
84	.ta \\n()Au \\n()Bu
85	.ie !"\\$3"" \{\
86	\&\\$1 \\fI\\$2\\fP (\\$3)
87	.\".b
88	.\}
89	.el \{\
90	.br
91	.ie !"\\$2"" \{\
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107	..
108	.AS Tcl_Interp Tcl_CreateInterp in/out
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128	.\" Draw four-sided box normally, but don't draw top of
129	.\" box if the box started on an earlier page.
130	.ie !\\n(^b-1 \{\
131	\h'-1.5n'\L'\|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'\|0u-1.5n\(ul'
132	.\}
133	.el \}\
134	\h'-1.5n'\L'\|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'\|0u-1.5n\(ul'
135	.\}
136	.\}
137	.fi
138	.br
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162	.\}
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175	.\" draw two sides but no top otherwise.
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177	.el \h'-1.5n'\L'\|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'\|0u'\c
178	.\}
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193	..
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201	.de DE
202	.fi
203	.RE
204	.sp
205	..
206	'\" # SO - start of list of standard options
207	.de SO
208	.SH "STANDARD OPTIONS"
209	.LP
210	.nf
211	.ta 5.5c 11c
212	.ft B
213	..
214	'\" # SE - end of list of standard options
215	.de SE
216	.fi
217	.ft R
218	.LP
219	See the \\fBoptions\\fR manual entry for details on the standard options.
220	..
221	'\" # OP - start of full description for a single option
222	.de OP
223	.LP
224	.nf
225	.ta 4c
226	Command-Line Name: \\fB\\$1\\fR
227	Database Name: \\fB\\$2\\fR
228	Database Class: \\fB\\$3\\fR
229	.fi
230	.IP
231	..
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240	.fi
241	.RE
242	..
243	.de UL
244	\\$1\l'\|0\(ul'\\$2
245	..
246	.TH Tcl_Preserve 3 7.5 Tcl "Tcl Library Procedures"
247	.BS
248	.SH NAME
249	Tcl_Preserve, Tcl_Release, Tcl_EventuallyFree \- avoid freeing storage while it's being used
250	.SH SYNOPSIS
251	.nf
252	\fB#include <tcl.h>\fR
253	.sp
254	\fBTcl_Preserve\fR(\fIclientData\fR)
255	.sp
256	\fBTcl_Release\fR(\fIclientData\fR)
257	.sp
258	\fBTcl_EventuallyFree\fR(\fIclientData, freeProc\fR)
259	.SH ARGUMENTS
260	.AS Tcl_FreeProc clientData
261	.AP ClientData clientData in
262	Token describing structure to be freed or reallocated. Usually a pointer
263	to memory for structure.
264	.AP Tcl_FreeProc *freeProc in
265	Procedure to invoke to free \fIclientData\fR.
266	.BE
267
268	.SH DESCRIPTION
269	.PP
270	These three procedures help implement a simple reference count mechanism
271	for managing storage. They are designed to solve a problem
272	having to do with widget deletion, but are also useful in many other
273	situations. When a widget is deleted, its
274	widget record (the structure holding information specific to the
275	widget) must be returned to the storage allocator.
276	However, it's possible that the widget record is in active use
277	by one of the procedures on the stack at the time of the deletion.
278	This can happen, for example, if the command associated with a button
279	widget causes the button to be destroyed: an X event causes an
280	event-handling C procedure in the button to be invoked, which in
281	turn causes the button's associated Tcl command to be executed,
282	which in turn causes the button to be deleted, which in turn causes
283	the button's widget record to be de-allocated.
284	Unfortunately, when the Tcl command returns, the button's
285	event-handling procedure will need to reference the
286	button's widget record.
287	Because of this, the widget record must not be freed as part of the
288	deletion, but must be retained until the event-handling procedure has
289	finished with it.
290	In other situations where the widget is deleted, it may be possible
291	to free the widget record immediately.
292	.PP
293	\fBTcl_Preserve\fR and \fBTcl_Release\fR
294	implement short-term reference counts for their \fIclientData\fR
295	argument.
296	The \fIclientData\fR argument identifies an object and usually
297	consists of the address of a structure.
298	The reference counts guarantee that an object will not be freed
299	until each call to \fBTcl_Preserve\fR for the object has been
300	matched by calls to \fBTcl_Release\fR.
301	There may be any number of unmatched \fBTcl_Preserve\fR calls
302	in effect at once.
303	.PP
304	\fBTcl_EventuallyFree\fR is invoked to free up its \fIclientData\fR
305	argument.
306	It checks to see if there are unmatched \fBTcl_Preserve\fR calls
307	for the object.
308	If not, then \fBTcl_EventuallyFree\fR calls \fIfreeProc\fR immediately.
309	Otherwise \fBTcl_EventuallyFree\fR records the fact that \fIclientData\fR
310	needs eventually to be freed.
311	When all calls to \fBTcl_Preserve\fR have been matched with
312	calls to \fBTcl_Release\fR then \fIfreeProc\fR will be called by
313	\fBTcl_Release\fR to do the cleanup.
314	.PP
315	All the work of freeing the object is carried out by \fIfreeProc\fR.
316	\fIFreeProc\fR must have arguments and result that match the
317	type \fBTcl_FreeProc\fR:
318	.CS
319	typedef void Tcl_FreeProc(char *\fIblockPtr\fR);
320	.CE
321	The \fIblockPtr\fR argument to \fIfreeProc\fR will be the
322	same as the \fIclientData\fR argument to \fBTcl_EventuallyFree\fR.
323	The type of \fIblockPtr\fR (\fBchar *\fR) is different than the type of the
324	\fIclientData\fR argument to \fBTcl_EventuallyFree\fR for historical
325	reasons, but the value is the same.
326	.PP
327	When the \fIclientData\fR argument to \fBTcl_EventuallyFree\fR
328	refers to storage allocated and returned by a prior call to
329	\fBTcl_Alloc\fR, \fBckalloc\fR, or another function of the Tcl library,
330	then the \fIfreeProc\fR argument should be given the special value of
331	\fBTCL_DYNAMIC\fR.
332	.PP
333	This mechanism can be used to solve the problem described above
334	by placing \fBTcl_Preserve\fR and \fBTcl_Release\fR calls around
335	actions that may cause undesired storage re-allocation. The
336	mechanism is intended only for short-term use (i.e. while procedures
337	are pending on the stack); it will not work efficiently as a
338	mechanism for long-term reference counts.
339	The implementation does not depend in any way on the internal
340	structure of the objects being freed; it keeps the reference
341	counts in a separate structure.
342
343	.SH "SEE ALSO"
344	Tcl_Interp, Tcl_Alloc
345
346	.SH KEYWORDS
347	free, reference count, storage