diff options
Diffstat (limited to 'doc/TraceVar.3')
| -rw-r--r-- | doc/TraceVar.3 | 105 |
1 files changed, 43 insertions, 62 deletions
diff --git a/doc/TraceVar.3 b/doc/TraceVar.3 index 0807a7e..022ef40 100644 --- a/doc/TraceVar.3 +++ b/doc/TraceVar.3 @@ -5,7 +5,7 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: TraceVar.3,v 1.8 2002/08/05 03:24:39 dgp Exp $ +'\" RCS: @(#) $Id: TraceVar.3,v 1.19 2007/12/13 15:22:32 dgp Exp $ '\" .so man.macros .TH Tcl_TraceVar 3 7.4 Tcl "Tcl Library Procedures" @@ -35,23 +35,24 @@ ClientData .AS Tcl_VarTraceProc prevClientData .AP Tcl_Interp *interp in Interpreter containing variable. -.AP "CONST char" *varName in +.AP "const char" *varName in Name of variable. May refer to a scalar variable, to an array variable with no index, or to an array variable with a parenthesized index. .AP int flags in -OR-ed combination of the values TCL_TRACE_READS, TCL_TRACE_WRITES, -TCL_TRACE_UNSETS, TCL_TRACE_ARRAY, TCL_GLOBAL_ONLY, TCL_NAMESPACE_ONLY, -TCL_TRACE_RESULT_DYNAMIC and TCL_TRACE_RESULT_OBJECT. +OR-ed combination of the values \fBTCL_TRACE_READS\fR, +\fBTCL_TRACE_WRITES\fR, \fBTCL_TRACE_UNSETS\fR, \fBTCL_TRACE_ARRAY\fR, +\fBTCL_GLOBAL_ONLY\fR, \fBTCL_NAMESPACE_ONLY\fR, +\fBTCL_TRACE_RESULT_DYNAMIC\fR and \fBTCL_TRACE_RESULT_OBJECT\fR. Not all flags are used by all procedures. See below for more information. .AP Tcl_VarTraceProc *proc in Procedure to invoke whenever one of the traced operations occurs. .AP ClientData clientData in Arbitrary one-word value to pass to \fIproc\fR. -.AP "CONST char" *name1 in +.AP "const char" *name1 in Name of scalar or array variable (without array index). -.AP "CONST char" *name2 in +.AP "const char" *name2 in For a trace on an element of an array, gives the index of the element. For traces on scalar variables or on whole arrays, is NULL. @@ -61,15 +62,14 @@ If non-NULL, gives last value returned by \fBTcl_VarTraceInfo\fR or next trace. If NULL, this call will return information about first trace. .BE - .SH DESCRIPTION .PP \fBTcl_TraceVar\fR allows a C procedure to monitor and control access to a Tcl variable, so that the C procedure is invoked whenever the variable is read or written or unset. If the trace is created successfully then \fBTcl_TraceVar\fR returns -TCL_OK. If an error occurred (e.g. \fIvarName\fR specifies an element -of an array, but the actual variable isn't an array) then TCL_ERROR +\fBTCL_OK\fR. If an error occurred (e.g. \fIvarName\fR specifies an element +of an array, but the actual variable is not an array) then \fBTCL_ERROR\fR is returned and an error message is left in the interpreter's result. .PP The \fIflags\fR argument to \fBTcl_TraceVar\fR indicates when the @@ -105,21 +105,19 @@ Invoke \fIproc\fR whenever the array command is invoked. This gives the trace procedure a chance to update the array before array names or array get is called. Note that this is called before an array set, but that will trigger write traces. -.VS 8.4 .TP \fBTCL_TRACE_RESULT_DYNAMIC\fR The result of invoking the \fIproc\fR is a dynamically allocated string that will be released by the Tcl library via a call to \fBckfree\fR. Must not be specified at the same time as -TCL_TRACE_RESULT_OBJECT. +\fBTCL_TRACE_RESULT_OBJECT\fR. .TP \fBTCL_TRACE_RESULT_OBJECT\fR The result of invoking the \fIproc\fR is a Tcl_Obj* (cast to a char*) with a reference count of at least one. The ownership of that reference will be transferred to the Tcl core for release (when the core has finished with it) via a call to \fBTcl_DecrRefCount\fR. Must -not be specified at the same time as TCL_TRACE_RESULT_DYNAMIC. -.VE 8.4 +not be specified at the same time as \fBTCL_TRACE_RESULT_DYNAMIC\fR. .PP Whenever one of the specified operations occurs on the variable, \fIproc\fR will be invoked. @@ -127,11 +125,11 @@ It should have arguments and result that match the type \fBTcl_VarTraceProc\fR: .CS typedef char *Tcl_VarTraceProc( - ClientData \fIclientData\fR, - Tcl_Interp *\fIinterp\fR, - char *\fIname1\fR, - char *\fIname2\fR, - int \fIflags\fR); + ClientData \fIclientData\fR, + Tcl_Interp *\fIinterp\fR, + char *\fIname1\fR, + char *\fIname2\fR, + int \fIflags\fR); .CE The \fIclientData\fR and \fIinterp\fR parameters will have the same values as those passed to \fBTcl_TraceVar\fR when the @@ -144,30 +142,30 @@ in the normal two-part form (see the description of \fBTcl_TraceVar2\fR below for details). \fIFlags\fR is an OR-ed combination of bits providing several pieces of information. -One of the bits TCL_TRACE_READS, TCL_TRACE_WRITES, TCL_TRACE_ARRAY, -or TCL_TRACE_UNSETS +One of the bits \fBTCL_TRACE_READS\fR, \fBTCL_TRACE_WRITES\fR, +\fBTCL_TRACE_ARRAY\fR, or \fBTCL_TRACE_UNSETS\fR will be set in \fIflags\fR to indicate which operation is being performed on the variable. -The bit TCL_GLOBAL_ONLY will be set whenever the variable being +The bit \fBTCL_GLOBAL_ONLY\fR will be set whenever the variable being accessed is a global one not accessible from the current level of procedure call: the trace procedure will need to pass this flag back to variable-related procedures like \fBTcl_GetVar\fR if it attempts to access the variable. -The bit TCL_NAMESPACE_ONLY will be set whenever the variable being +The bit \fBTCL_NAMESPACE_ONLY\fR will be set whenever the variable being accessed is a namespace one not accessible from the current level of procedure call: the trace procedure will need to pass this flag back to variable-related procedures like \fBTcl_GetVar\fR if it attempts to access the variable. -The bit TCL_TRACE_DESTROYED will be set in \fIflags\fR if the trace is +The bit \fBTCL_TRACE_DESTROYED\fR will be set in \fIflags\fR if the trace is about to be destroyed; this information may be useful to \fIproc\fR so that it can clean up its own internal data structures (see -the section TCL_TRACE_DESTROYED below for more details). -Lastly, the bit TCL_INTERP_DESTROYED will be set if the entire +the section \fBTCL_TRACE_DESTROYED\fR below for more details). +Lastly, the bit \fBTCL_INTERP_DESTROYED\fR will be set if the entire interpreter is being destroyed. When this bit is set, \fIproc\fR must be especially careful in -the things it does (see the section TCL_INTERP_DESTROYED below). +the things it does (see the section \fBTCL_INTERP_DESTROYED\fR below). The trace procedure's return value should normally be NULL; see -ERROR RETURNS below for information on other possibilities. +\fBERROR RETURNS\fR below for information on other possibilities. .PP \fBTcl_UntraceVar\fR may be used to remove a trace. If the variable specified by \fIinterp\fR, \fIvarName\fR, and \fIflags\fR @@ -182,14 +180,14 @@ traces set on a given variable. The return value from \fBTcl_VarTraceInfo\fR is the \fIclientData\fR associated with a particular trace. The trace must be on the variable specified by the \fIinterp\fR, -\fIvarName\fR, and \fIflags\fR arguments (only the TCL_GLOBAL_ONLY and -TCL_NAMESPACE_ONLY bits from \fIflags\fR is used; other bits are +\fIvarName\fR, and \fIflags\fR arguments (only the \fBTCL_GLOBAL_ONLY\fR and +\fBTCL_NAMESPACE_ONLY\fR bits from \fIflags\fR is used; other bits are ignored) and its trace procedure must the same as the \fIproc\fR argument. If the \fIprevClientData\fR argument is NULL then the return value corresponds to the first (most recently created) matching trace, or NULL if there are no matching traces. -If the \fIprevClientData\fR argument isn't NULL, then it should +If the \fIprevClientData\fR argument is not NULL, then it should be the return value from a previous call to \fBTcl_VarTraceInfo\fR. In this case, the new return value will correspond to the next matching trace after the one whose \fIclientData\fR matches @@ -197,7 +195,6 @@ matching trace after the one whose \fIclientData\fR matches or if there are no more matching traces after it. This mechanism makes it possible to step through all of the traces for a given variable that have the same \fIproc\fR. - .SH "TWO-PART NAMES" .PP The procedures \fBTcl_TraceVar2\fR, \fBTcl_UntraceVar2\fR, and @@ -206,7 +203,6 @@ The procedures \fBTcl_TraceVar2\fR, \fBTcl_UntraceVar2\fR, and except that the name of the variable consists of two parts. \fIName1\fR gives the name of a scalar variable or array, and \fIname2\fR gives the name of an element within an array. -.VS 8.1 When \fIname2\fR is NULL, \fIname1\fR may contain both an array and an element name: if the name contains an open parenthesis and ends with a @@ -215,14 +211,10 @@ treated as an element name (which can have any string value) and the characters before the first open parenthesis are treated as the name of an array variable. If \fIname2\fR is NULL and \fIname1\fR does not refer -to an array element -.VE -it means that either the variable is +to an array element it means that either the variable is a scalar or the trace is to be set on the entire array rather than an individual element (see WHOLE-ARRAY TRACES below for more information). - - .SH "ACCESSING VARIABLES DURING TRACES" .PP During read, write, and array traces, the @@ -248,7 +240,6 @@ from the variable before any trace procedures are invoked. If new traces are set by unset trace procedures, these traces will be invoked on accesses to the variable by the trace procedures. - .SH "CALLBACK TIMING" .PP When read tracing has been specified for a variable, the trace @@ -288,7 +279,6 @@ When unset tracing has been specified, the trace procedure will be invoked whenever the variable is destroyed. The traces will be called after the variable has been completely unset. - .SH "WHOLE-ARRAY TRACES" .PP If a call to \fBTcl_TraceVar\fR or \fBTcl_TraceVar2\fR specifies @@ -301,7 +291,6 @@ When an array is unset, a whole-array trace will be invoked just once, with \fIname1\fR equal to the name of the array and \fIname2\fR NULL; it will not be invoked once for each element. - .SH "MULTIPLE TRACES" .PP It is possible for multiple traces to exist on the same variable. @@ -313,7 +302,6 @@ before the individual-element traces. If a read or write trace unsets the variable then all of the unset traces will be invoked but the remainder of the read and write traces will be skipped. - .SH "ERROR RETURNS" .PP Under normal conditions trace procedures should return NULL, indicating @@ -322,13 +310,11 @@ If \fIproc\fR returns a non-NULL value it signifies that an error occurred. The return value must be a pointer to a static character string containing an error message, -.VS 8.4 -unless (\fIexactly\fR one of) the TCL_TRACE_RESULT_DYNAMIC and -TCL_TRACE_RESULT_OBJECT flags is set, which specify that the result is +unless (\fIexactly\fR one of) the \fBTCL_TRACE_RESULT_DYNAMIC\fR and +\fBTCL_TRACE_RESULT_OBJECT\fR flags is set, which specify that the result is either a dynamic string (to be released with \fBckfree\fR) or a Tcl_Obj* (cast to char* and to be released with \fBTcl_DecrRefCount\fR) containing the error message. -.VE 8.4 If a trace procedure returns an error, no further traces are invoked for the access and the traced access aborts with the given message. @@ -342,56 +328,51 @@ The return value from \fIproc\fR is only used during read and write tracing. During unset traces, the return value is ignored and all relevant trace procedures will always be invoked. - .SH "RESTRICTIONS" .PP A trace procedure can be called at any time, even when there -is a partially-formed result in the interpreter's result area. If +is a partially formed result in the interpreter's result area. If the trace procedure does anything that could damage this result (such as calling \fBTcl_Eval\fR) then it must save the original values of the interpreter's \fBresult\fR and \fBfreeProc\fR fields and restore them before it returns. - .SH "UNDEFINED VARIABLES" .PP It is legal to set a trace on an undefined variable. The variable will still appear to be undefined until the first time its value is set. If an undefined variable is traced and then unset, the unset will fail -with an error (``no such variable''), but the trace -procedure will still be invoked. - +with an error +.PQ "no such variable" "" , +but the trace procedure will still be invoked. .SH "TCL_TRACE_DESTROYED FLAG" .PP -In an unset callback to \fIproc\fR, the TCL_TRACE_DESTROYED bit +In an unset callback to \fIproc\fR, the \fBTCL_TRACE_DESTROYED\fR bit is set in \fIflags\fR if the trace is being removed as part of the deletion. Traces on a variable are always removed whenever the variable -is deleted; the only time TCL_TRACE_DESTROYED isn't set is for +is deleted; the only time \fBTCL_TRACE_DESTROYED\fR is not set is for a whole-array trace invoked when only a single element of an array is unset. - .SH "TCL_INTERP_DESTROYED" .PP When an interpreter is destroyed, unset traces are called for all of its variables. -The TCL_INTERP_DESTROYED bit will be set in the \fIflags\fR +The \fBTCL_INTERP_DESTROYED\fR bit will be set in the \fIflags\fR argument passed to the trace procedures. Trace procedures must be extremely careful in what they do if -the TCL_INTERP_DESTROYED bit is set. +the \fBTCL_INTERP_DESTROYED\fR bit is set. It is not safe for the procedures to invoke any Tcl procedures on the interpreter, since its state is partially deleted. All that trace procedures should do under these circumstances is to clean up and free their own internal data structures. - .SH BUGS .PP -Tcl doesn't do any error checking to prevent trace procedures -from misusing the interpreter during traces with TCL_INTERP_DESTROYED +Tcl does not do any error checking to prevent trace procedures +from misusing the interpreter during traces with \fBTCL_INTERP_DESTROYED\fR set. .PP -Array traces are not yet integrated with the Tcl "info exists" command, +Array traces are not yet integrated with the Tcl \fBinfo exists\fR command, nor is there Tcl-level access to array traces. - .SH KEYWORDS clientData, trace, variable |