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Diffstat (limited to 'tcl/doc/trace.n')
| -rw-r--r-- | tcl/doc/trace.n | 373 |
1 files changed, 286 insertions, 87 deletions
diff --git a/tcl/doc/trace.n b/tcl/doc/trace.n index 5ead91597f1..7d111fd1eba 100644 --- a/tcl/doc/trace.n +++ b/tcl/doc/trace.n @@ -1,6 +1,7 @@ '\" '\" Copyright (c) 1993 The Regents of the University of California. '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. +'\" Copyright (c) 2000 Ajuba Solutions. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. @@ -8,11 +9,11 @@ '\" RCS: @(#) $Id$ '\" .so man.macros -.TH trace n "" Tcl "Tcl Built-In Commands" +.TH trace n "8.4" Tcl "Tcl Built-In Commands" .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME -trace \- Monitor variable accesses +trace \- Monitor variable accesses, command usages and command executions .SH SYNOPSIS \fBtrace \fIoption\fR ?\fIarg arg ...\fR? .BE @@ -20,12 +21,151 @@ trace \- Monitor variable accesses .SH DESCRIPTION .PP This command causes Tcl commands to be executed whenever certain operations are -invoked. At present, only variable tracing is implemented. The -legal \fIoption\fR's (which may be abbreviated) are: +invoked. The legal \fIoption\fR's (which may be abbreviated) are: .TP -\fBtrace variable \fIname ops command\fR +\fBtrace add \fItype name ops ?args?\fR +Where \fItype\fR is \fBcommand\fR, \fBexecution\fR, or \fBvariable\fR. +.RS +.TP +\fBtrace add command\fR \fIname ops command\fR +Arrange for \fIcommand\fR to be executed whenever command \fIname\fR +is modified in one of the ways given by the list \fIops\fR. \fIName\fR will be +resolved using the usual namespace resolution rules used by +procedures. If the command does not exist, an error will be thrown. +.RS +.PP +\fIOps\fR indicates which operations are of interest, and is a list of +one or more of the following items: +.TP +\fBrename\fR +Invoke \fIcommand\fR whenever the command is renamed. Note that +renaming to the empty string is considered deletion, and will not +be traced with '\fBrename\fR'. +.TP +\fBdelete\fR +Invoke \fIcommand\fR when the command is deleted. Commands can be +deleted explicitly by using the \fBrename\fR command to rename the +command to an empty string. Commands are also deleted when the +interpreter is deleted, but traces will not be invoked because there is no +interpreter in which to execute them. +.PP +When the trace triggers, depending on the operations being traced, a +number of arguments are appended to \fIcommand\fR so that the actual +command is as follows: +.CS +\fIcommand oldName newName op\fR +.CE +\fIOldName\fR and \fInewName\fR give the traced command's current +(old) name, and the name to which it is being renamed (the empty +string if this is a 'delete' operation). +\fIOp\fR indicates what operation is being performed on the +command, and is one of \fBrename\fR or \fBdelete\fR as +defined above. The trace operation cannot be used to stop a command +from being deleted. Tcl will always remove the command once the trace +is complete. Recursive renaming or deleting will not cause further traces +of the same type to be evaluated, so a delete trace which itself +deletes the command, or a rename trace which itself renames the +command will not cause further trace evaluations to occur. +.RE +.TP +\fBtrace add execution\fR \fIname ops command\fR +Arrange for \fIcommand\fR to be executed whenever command \fIname\fR +is modified in one of the ways given by the list \fIops\fR. \fIName\fR will be +resolved using the usual namespace resolution rules used by +procedures. If the command does not exist, an error will be thrown. +.RS +.PP +\fIOps\fR indicates which operations are of interest, and is a list of +one or more of the following items: +.TP +\fBenter\fR +Invoke \fIcommand\fR whenever the command \fIname\fR is executed, +just before the actual execution takes place. +.TP +\fBleave\fR +Invoke \fIcommand\fR whenever the command \fIname\fR is executed, +just after the actual execution takes place. +.TP +\fBenterstep\fR +Invoke \fIcommand\fR for every tcl command which is executed +inside the procedure \fIname\fR, just before the actual execution +takes place. For example if we have 'proc foo {} { puts "hello" }', +then a \fIenterstep\fR trace would be +invoked just before \fIputs "hello"\fR is executed. +Setting a \fIenterstep\fR trace on a \fIcommand\fR +will not result in an error and is simply ignored. +.TP +\fBleavestep\fR +Invoke \fIcommand\fR for every tcl command which is executed +inside the procedure \fIname\fR, just after the actual execution +takes place. +Setting a \fIleavestep\fR trace on a \fIcommand\fR +will not result in an error and is simply ignored. +.PP +When the trace triggers, depending on the operations being traced, a +number of arguments are appended to \fIcommand\fR so that the actual +command is as follows: + +For \fBenter\fR and \fBenterstep\fR operations: +.CS +\fIcommand command-string op\fR +.CE +\fICommand-string\fR gives the complete current command being +executed (the traced command for a \fBenter\fR operation, an +arbitrary command for a \fBenterstep\fR operation), including +all arguments in their fully expanded form. +\fIOp\fR indicates what operation is being performed on the +command execution, and is one of \fBenter\fR or \fBenterstep\fR as +defined above. The trace operation can be used to stop the +command from executing, by deleting the command in question. Of +course when the command is subsequently executed, an 'invalid command' +error will occur. +.TP +For \fBleave\fR and \fBleavestep\fR operations: +.CS +\fIcommand command-string code result op\fR +.CE +\fICommand-string\fR gives the complete current command being +executed (the traced command for a \fBenter\fR operation, an +arbitrary command for a \fBenterstep\fR operation), including +all arguments in their fully expanded form. +\fICode\fR gives the result code of that execution, and \fIresult\fR +the result string. +\fIOp\fR indicates what operation is being performed on the +command execution, and is one of \fBleave\fR or \fBleavestep\fR as +defined above. +Note that the creation of many \fBenterstep\fR or +\fBleavestep\fR traces can lead to unintuitive results, since the +invoked commands from one trace can themselves lead to further +command invocations for other traces. + +\fICommand\fR executes in the same context as the code that invoked +the traced operation: thus the \fIcommand\fR, if invoked from a procedure, +will have access to the same local variables as code in the procedure. +This context may be different than the context in which the trace was +created. If \fIcommand\fR invokes a procedure (which it normally does) +then the procedure will have to use upvar or uplevel commands if it wishes +to access the local variables of the code which invoked the trace operation. + +While \fIcommand\fR is executing during an execution trace, traces +on \fIname\fR are temporarily disabled. This allows the \fIcommand\fR +to execute \fIname\fR in its body without invoking any other traces again. +If an error occurs while executing the \fIcommand\fR body, then the +\fIcommand\fR name as a whole will return that same error. + +When multiple traces are set on \fIname\fR, then for \fIenter\fR +and \fIenterstep\fR operations, the traced commands are invoked +in the reverse order of how the traces were originally created; +and for \fIleave\fR and \fIleavestep\fR operations, the traced +commands are invoked in the original order of creation. + +The behavior of execution traces is currently undefined for a command +\fIname\fR imported into another namespace. +.RE +.TP +\fBtrace add variable\fI name ops command\fR Arrange for \fIcommand\fR to be executed whenever variable \fIname\fR -is accessed in one of the ways given by \fIops\fR. \fIName\fR may +is accessed in one of the ways given by the list \fIops\fR. \fIName\fR may refer to a normal variable, an element of an array, or to an array as a whole (i.e. \fIname\fR may be just the name of an array, with no parenthesized index). If \fIname\fR refers to a whole array, then @@ -35,16 +175,23 @@ will not be given a value, so it will be visible to \fBnamespace which\fR queries, but not to \fBinfo exists\fR queries. .RS .PP -\fIOps\fR indicates which operations are of interest, and consists of -one or more of the following letters: +\fIOps\fR indicates which operations are of interest, and is a list of +one or more of the following items: +.TP +\fBarray\fR +Invoke \fIcommand\fR whenever the variable is accessed or modified via +the \fBarray\fR command, provided that \fIname\fR is not a scalar +variable at the time that the \fBarray\fR command is invoked. If +\fIname\fR is a scalar variable, the access via the \fBarray\fR +command will not trigger the trace. .TP -\fBr\fR +\fBread\fR Invoke \fIcommand\fR whenever the variable is read. .TP -\fBw\fR +\fBwrite\fR Invoke \fIcommand\fR whenever the variable is written. .TP -\fBu\fR +\fBunset\fR Invoke \fIcommand\fR whenever the variable is unset. Variables can be unset explicitly with the \fBunset\fR command, or implicitly when procedures return (all of their local variables @@ -70,91 +217,143 @@ name used in the \fBtrace variable\fR command: the \fBupvar\fR command allows a procedure to reference a variable under a different name. \fIOp\fR indicates what operation is being performed on the -variable, and is one of \fBr\fR, \fBw\fR, or \fBu\fR as +variable, and is one of \fBread\fR, \fBwrite\fR, or \fBunset\fR as defined above. .PP \fICommand\fR executes in the same context as the code that invoked -the traced operation: if the variable was accessed as part of a -Tcl procedure, then \fIcommand\fR will have access to the same -local variables as code in the procedure. This context may be -different than the context in which the trace was created. -If \fIcommand\fR invokes a procedure (which it normally does) then -the procedure will have to use \fBupvar\fR or \fBuplevel\fR if it -wishes to access the traced variable. -Note also that \fIname1\fR may not necessarily be the same as the name -used to set the trace on the variable; differences can occur if -the access is made through a variable defined with the \fBupvar\fR -command. -.PP -For read and write traces, \fIcommand\fR can modify -the variable to affect the result of the traced operation. -If \fIcommand\fR modifies the value of a variable during a -read or write trace, then the new value will be returned as the -result of the traced operation. -The return value from \fIcommand\fR is ignored except that -if it returns an error of any sort then the traced operation -also returns an error with -the same error message returned by the trace command -(this mechanism can be used to implement read-only variables, for -example). -For write traces, \fIcommand\fR is invoked after the variable's -value has been changed; it can write a new value into the variable -to override the original value specified in the write operation. -To implement read-only variables, \fIcommand\fR will have to restore -the old value of the variable. +the traced operation: if the variable was accessed as part of a Tcl +procedure, then \fIcommand\fR will have access to the same local +variables as code in the procedure. This context may be different +than the context in which the trace was created. If \fIcommand\fR +invokes a procedure (which it normally does) then the procedure will +have to use \fBupvar\fR or \fBuplevel\fR if it wishes to access the +traced variable. Note also that \fIname1\fR may not necessarily be +the same as the name used to set the trace on the variable; +differences can occur if the access is made through a variable defined +with the \fBupvar\fR command. +.PP +For read and write traces, \fIcommand\fR can modify the variable to +affect the result of the traced operation. If \fIcommand\fR modifies +the value of a variable during a read or write trace, then the new +value will be returned as the result of the traced operation. The +return value from \fIcommand\fR is ignored except that if it returns +an error of any sort then the traced operation also returns an error +with the same error message returned by the trace command (this +mechanism can be used to implement read-only variables, for example). +For write traces, \fIcommand\fR is invoked after the variable's value +has been changed; it can write a new value into the variable to +override the original value specified in the write operation. To +implement read-only variables, \fIcommand\fR will have to restore the +old value of the variable. .PP While \fIcommand\fR is executing during a read or write trace, traces -on the variable are temporarily disabled. -This means that reads and writes invoked by -\fIcommand\fR will occur directly, without invoking \fIcommand\fR -(or any other traces) again. -However, if \fIcommand\fR unsets the variable then unset traces -will be invoked. -.PP -When an unset trace is invoked, the variable has already been -deleted: it will appear to be undefined with no traces. -If an unset occurs because of a procedure return, then the -trace will be invoked in the variable context of the procedure -being returned to: the stack frame of the returning procedure -will no longer exist. -Traces are not disabled during unset traces, so if an unset trace -command creates a new trace and accesses the variable, the -trace will be invoked. -Any errors in unset traces are ignored. -.PP -If there are multiple traces on a variable they are invoked -in order of creation, most-recent first. -If one trace returns an error, then no further traces are -invoked for the variable. -If an array element has a trace set, and there is also a trace -set on the array as a whole, the trace on the overall array -is invoked before the one on the element. -.PP -Once created, the trace remains in effect either until the -trace is removed with the \fBtrace vdelete\fR command described -below, until the variable is unset, or until the interpreter -is deleted. -Unsetting an element of array will remove any traces on that -element, but will not remove traces on the overall array. +on the variable are temporarily disabled. This means that reads and +writes invoked by \fIcommand\fR will occur directly, without invoking +\fIcommand\fR (or any other traces) again. However, if \fIcommand\fR +unsets the variable then unset traces will be invoked. +.PP +When an unset trace is invoked, the variable has already been deleted: +it will appear to be undefined with no traces. If an unset occurs +because of a procedure return, then the trace will be invoked in the +variable context of the procedure being returned to: the stack frame +of the returning procedure will no longer exist. Traces are not +disabled during unset traces, so if an unset trace command creates a +new trace and accesses the variable, the trace will be invoked. Any +errors in unset traces are ignored. +.PP +If there are multiple traces on a variable they are invoked in order +of creation, most-recent first. If one trace returns an error, then +no further traces are invoked for the variable. If an array element +has a trace set, and there is also a trace set on the array as a +whole, the trace on the overall array is invoked before the one on the +element. +.PP +Once created, the trace remains in effect either until the trace is +removed with the \fBtrace remove variable\fR command described below, +until the variable is unset, or until the interpreter is deleted. +Unsetting an element of array will remove any traces on that element, +but will not remove traces on the overall array. .PP This command returns an empty string. .RE +.RE +.TP +\fBtrace remove \fItype name opList command\fR +Where \fItype\fR is either \fBcommand\fR, \fBexecution\fR or \fBvariable\fR. +.RS +.TP +\fBtrace remove command\fI name opList command\fR +If there is a trace set on command \fIname\fR with the operations and +command given by \fIopList\fR and \fIcommand\fR, then the trace is +removed, so that \fIcommand\fR will never again be invoked. Returns +an empty string. If \fIname\fR doesn't exist, the command will throw +an error. +.TP +\fBtrace remove execution\fI name opList command\fR +If there is a trace set on command \fIname\fR with the operations and +command given by \fIopList\fR and \fIcommand\fR, then the trace is +removed, so that \fIcommand\fR will never again be invoked. Returns +an empty string. If \fIname\fR doesn't exist, the command will throw +an error. +.TP +\fBtrace remove variable\fI name opList command\fR +If there is a trace set on variable \fIname\fR with the operations and +command given by \fIopList\fR and \fIcommand\fR, then the trace is +removed, so that \fIcommand\fR will never again be invoked. Returns +an empty string. +.RE +.TP +\fBtrace info \fItype name\fR +Where \fItype\fR is either \fBcommand\fR, \fBexecution\fR or \fBvariable\fR. +.RS +.TP +\fBtrace info command\fI name\fR +Returns a list containing one element for each trace currently set on +command \fIname\fR. Each element of the list is itself a list +containing two elements, which are the \fIopList\fR and \fIcommand\fR +associated with the trace. If \fIname\fR doesn't have any traces set, +then the result of the command will be an empty string. If \fIname\fR +doesn't exist, the command will throw an error. +.TP +\fBtrace info execution\fI name\fR +Returns a list containing one element for each trace currently set on +command \fIname\fR. Each element of the list is itself a list +containing two elements, which are the \fIopList\fR and \fIcommand\fR +associated with the trace. If \fIname\fR doesn't have any traces set, +then the result of the command will be an empty string. If \fIname\fR +doesn't exist, the command will throw an error. +.TP +\fBtrace info variable\fI name\fR +Returns a list containing one element for each trace currently set on +variable \fIname\fR. Each element of the list is itself a list +containing two elements, which are the \fIopList\fR and \fIcommand\fR +associated with the trace. If \fIname\fR doesn't exist or doesn't +have any traces set, then the result of the command will be an empty +string. +.RE +.PP +For backwards compatibility, three other subcommands are available: +.RS +.TP +\fBtrace variable \fIname ops command\fR +This is equivalent to \fBtrace add variable \fIname ops command\fR. .TP \fBtrace vdelete \fIname ops command\fR -If there is a trace set on variable \fIname\fR with the -operations and command given by \fIops\fR and \fIcommand\fR, -then the trace is removed, so that \fIcommand\fR will never -again be invoked. -Returns an empty string. -.TP -\fBtrace vinfo \fIname\fR -Returns a list containing one element for each trace -currently set on variable \fIname\fR. -Each element of the list is itself a list containing two -elements, which are the \fIops\fR and \fIcommand\fR associated -with the trace. -If \fIname\fR doesn't exist or doesn't have any traces set, then -the result of the command will be an empty string. +This is equivalent to \fBtrace remove variable \fIname ops command\fR +.TP +\fBtrace vinfo \fIname\fR +This is equivalent to \fBtrace info variable \fIname\fR +.RE +.PP +These subcommands are deprecated and will likely be removed in a +future version of Tcl. They use an older syntax in which \fBarray\fR, +\fBread\fR, \fBwrite\fR, \fBunset\fR are replaced by \fBa\fR, \fBr\fR, +\fBw\fR and \fBu\fR respectively, and the \fIops\fR argument is not a +list, but simply a string concatenation of the operations, such as +\fBrwua\fR. + +.SH "SEE ALSO" +set(n), unset(n) .SH KEYWORDS -read, variable, write, trace, unset +read, command, rename, variable, write, trace, unset |