/*
* tclLink.c --
*
* This file implements linked variables (a C variable that is
* tied to a Tcl variable). The idea of linked variables was
* first suggested by Andreas Stolcke and this implementation is
* based heavily on a prototype implementation provided by
* him.
*
* Copyright (c) 1993 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: tclLink.c,v 1.2 1998/09/14 18:40:00 stanton Exp $
*/
#include "tclInt.h"
/*
* For each linked variable there is a data structure of the following
* type, which describes the link and is the clientData for the trace
* set on the Tcl variable.
*/
typedef struct Link {
Tcl_Interp *interp; /* Interpreter containing Tcl variable. */
char *varName; /* Name of variable (must be global). This
* is needed during trace callbacks, since
* the actual variable may be aliased at
* that time via upvar. */
char *addr; /* Location of C variable. */
int type; /* Type of link (TCL_LINK_INT, etc.). */
union {
int i;
double d;
} lastValue; /* Last known value of C variable; used to
* avoid string conversions. */
int flags; /* Miscellaneous one-bit values; see below
* for definitions. */
} Link;
/*
* Definitions for flag bits:
* LINK_READ_ONLY - 1 means errors should be generated if Tcl
* script attempts to write variable.
* LINK_BEING_UPDATED - 1 means that a call to Tcl_UpdateLinkedVar
* is in progress for this variable, so
* trace callbacks on the variable should
* be ignored.
*/
#define LINK_READ_ONLY 1
#define LINK_BEING_UPDATED 2
/*
* Forward references to procedures defined later in this file:
*/
static char * LinkTraceProc _ANSI_ARGS_((ClientData clientData,
Tcl_Interp *interp, char *name1, char *name2,
int flags));
static char * StringValue _ANSI_ARGS_((Link *linkPtr,
char *buffer));
/*
*----------------------------------------------------------------------
*
* Tcl_LinkVar --
*
* Link a C variable to a Tcl variable so that changes to either
* one causes the other to change.
*
* Results:
* The return value is TCL_OK if everything went well or TCL_ERROR
* if an error occurred (interp->result is also set after errors).
*
* Side effects:
* The value at *addr is linked to the Tcl variable "varName",
* using "type" to convert between string values for Tcl and
* binary values for *addr.
*
*----------------------------------------------------------------------
*/
int
Tcl_LinkVar(interp, varName, addr, type)
Tcl_Interp *interp; /* Interpreter in which varName exists. */
char *varName; /* Name of a global variable in interp. */
char *addr; /* Address of a C variable to be linked
* to varName. */
int type; /* Type of C variable: TCL_LINK_INT, etc.
* Also may have TCL_LINK_READ_ONLY
* OR'ed in. */
{
Link *linkPtr;
char buffer[TCL_DOUBLE_SPACE];
int code;
linkPtr = (Link *) ckalloc(sizeof(Link));
linkPtr->interp = interp;
linkPtr->varName = (char *) ckalloc((unsigned) (strlen(varName) + 1));
strcpy(linkPtr->varName, varName);
linkPtr->addr = addr;
linkPtr->type = type & ~TCL_LINK_READ_ONLY;
if (type & TCL_LINK_READ_ONLY) {
linkPtr->flags = LINK_READ_ONLY;
} else {
linkPtr->flags = 0;
}
if (Tcl_SetVar(interp, varName, StringValue(linkPtr, buffer),
TCL_GLOBAL_ONLY|TCL_LEAVE_ERR_MSG) == NULL) {
ckfree(linkPtr->varName);
ckfree((char *) linkPtr);
return TCL_ERROR;
}
code = Tcl_TraceVar(interp, varName, TCL_GLOBAL_ONLY|TCL_TRACE_READS
|TCL_TRACE_WRITES|TCL_TRACE_UNSETS, LinkTraceProc,
(ClientData) linkPtr);
if (code != TCL_OK) {
ckfree(linkPtr->varName);
ckfree((char *) linkPtr);
}
return code;
}
/*
*----------------------------------------------------------------------
*
* Tcl_UnlinkVar --
*
* Destroy the link between a Tcl variable and a C variable.
*
* Results:
* None.
*
* Side effects:
* If "varName" was previously linked to a C variable, the link
* is broken to make the variable independent. If there was no
* previous link for "varName" then nothing happens.
*
*----------------------------------------------------------------------
*/
void
Tcl_UnlinkVar(interp, varName)
Tcl_Interp *interp; /* Interpreter containing variable to unlink. */
char *varName; /* Global variable in interp to unlink. */
{
Link *linkPtr;
linkPtr = (Link *) Tcl_VarTraceInfo(interp, varName, TCL_GLOBAL_ONLY,
LinkTraceProc, (ClientData) NULL);
if (linkPtr == NULL) {
return;
}
Tcl_UntraceVar(interp, varName,
TCL_GLOBAL_ONLY|TCL_TRACE_READS|TCL_TRACE_WRITES|TCL_TRACE_UNSETS,
LinkTraceProc, (ClientData) linkPtr);
ckfree(linkPtr->varName);
ckfree((char *) linkPtr);
}
/*
*----------------------------------------------------------------------
*
* Tcl_UpdateLinkedVar --
*
* This procedure is invoked after a linked variable has been
* changed by C code. It updates the Tcl variable so that
* traces on the variable will trigger.
*
* Results:
* None.
*
* Side effects:
* The Tcl variable "varName" is updated from its C value,
* causing traces on the variable to trigger.
*
*----------------------------------------------------------------------
*/
void
Tcl_UpdateLinkedVar(interp, varName)
Tcl_Interp *interp; /* Interpreter containing variable. */
char *varName; /* Name of global variable that is linked. */
{
Link *linkPtr;
char buffer[TCL_DOUBLE_SPACE];
int savedFlag;
linkPtr = (Link *) Tcl_VarTraceInfo(interp, varName, TCL_GLOBAL_ONLY,
LinkTraceProc, (ClientData) NULL);
if (linkPtr == NULL) {
return;
}
savedFlag = linkPtr->flags & LINK_BEING_UPDATED;
linkPtr->flags |= LINK_BEING_UPDATED;
Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
TCL_GLOBAL_ONLY);
linkPtr->flags = (linkPtr->flags & ~LINK_BEING_UPDATED) | savedFlag;
}
/*
*----------------------------------------------------------------------
*
* LinkTraceProc --
*
* This procedure is invoked when a linked Tcl variable is read,
* written, or unset from Tcl. It's responsible for keeping the
* C variable in sync with the Tcl variable.
*
* Results:
* If all goes well, NULL is returned; otherwise an error message
* is returned.
*
* Side effects:
* The C variable may be updated to make it consistent with the
* Tcl variable, or the Tcl variable may be overwritten to reject
* a modification.
*
*----------------------------------------------------------------------
*/
static char *
LinkTraceProc(clientData, interp, name1, name2, flags)
ClientData clientData; /* Contains information about the link. */
Tcl_Interp *interp; /* Interpreter containing Tcl variable. */
char *name1; /* First part of variable name. */
char *name2; /* Second part of variable name. */
int flags; /* Miscellaneous additional information. */
{
Link *linkPtr = (Link *) clientData;
int changed;
char buffer[TCL_DOUBLE_SPACE];
char *value, **pp;
Tcl_DString savedResult;
/*
* If the variable is being unset, then just re-create it (with a
* trace) unless the whole interpreter is going away.
*/
if (flags & TCL_TRACE_UNSETS) {
if (flags & TCL_INTERP_DESTROYED) {
ckfree(linkPtr->varName);
ckfree((char *) linkPtr);
} else if (flags & TCL_TRACE_DESTROYED) {
Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
TCL_GLOBAL_ONLY);
Tcl_TraceVar(interp, linkPtr->varName, TCL_GLOBAL_ONLY
|TCL_TRACE_READS|TCL_TRACE_WRITES|TCL_TRACE_UNSETS,
LinkTraceProc, (ClientData) linkPtr);
}
return NULL;
}
/*
* If we were invoked because of a call to Tcl_UpdateLinkedVar, then
* don't do anything at all. In particular, we don't want to get
* upset that the variable is being modified, even if it is
* supposed to be read-only.
*/
if (linkPtr->flags & LINK_BEING_UPDATED) {
return NULL;
}
/*
* For read accesses, update the Tcl variable if the C variable
* has changed since the last time we updated the Tcl variable.
*/
if (flags & TCL_TRACE_READS) {
switch (linkPtr->type) {
case TCL_LINK_INT:
case TCL_LINK_BOOLEAN:
changed = *(int *)(linkPtr->addr) != linkPtr->lastValue.i;
break;
case TCL_LINK_DOUBLE:
changed = *(double *)(linkPtr->addr) != linkPtr->lastValue.d;
break;
case TCL_LINK_STRING:
changed = 1;
break;
default:
return "internal error: bad linked variable type";
}
if (changed) {
Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
TCL_GLOBAL_ONLY);
}
return NULL;
}
/*
* For writes, first make sure that the variable is writable. Then
* convert the Tcl value to C if possible. If the variable isn't
* writable or can't be converted, then restore the varaible's old
* value and return an error. Another tricky thing: we have to save
* and restore the interpreter's result, since the variable access
* could occur when the result has been partially set.
*/
if (linkPtr->flags & LINK_READ_ONLY) {
Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
TCL_GLOBAL_ONLY);
return "linked variable is read-only";
}
value = Tcl_GetVar(interp, linkPtr->varName, TCL_GLOBAL_ONLY);
if (value == NULL) {
/*
* This shouldn't ever happen.
*/
return "internal error: linked variable couldn't be read";
}
Tcl_DStringInit(&savedResult);
Tcl_DStringAppend(&savedResult, interp->result, -1);
Tcl_ResetResult(interp);
switch (linkPtr->type) {
case TCL_LINK_INT:
if (Tcl_GetInt(interp, value, &linkPtr->lastValue.i) != TCL_OK) {
Tcl_DStringResult(interp, &savedResult);
Tcl_SetVar(interp, linkPtr->varName,
StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY);
return "variable must have integer value";
}
*(int *)(linkPtr->addr) = linkPtr->lastValue.i;
break;
case TCL_LINK_DOUBLE:
if (Tcl_GetDouble(interp, value, &linkPtr->lastValue.d)
!= TCL_OK) {
Tcl_DStringResult(interp, &savedResult);
Tcl_SetVar(interp, linkPtr->varName,
StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY);
return "variable must have real value";
}
*(double *)(linkPtr->addr) = linkPtr->lastValue.d;
break;
case TCL_LINK_BOOLEAN:
if (Tcl_GetBoolean(interp, value, &linkPtr->lastValue.i)
!= TCL_OK) {
Tcl_DStringResult(interp, &savedResult);
Tcl_SetVar(interp, linkPtr->varName,
StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY);
return "variable must have boolean value";
}
*(int *)(linkPtr->addr) = linkPtr->lastValue.i;
break;
case TCL_LINK_STRING:
pp = (char **)(linkPtr->addr);
if (*pp != NULL) {
ckfree(*pp);
}
*pp = (char *) ckalloc((unsigned) (strlen(value) + 1));
strcpy(*pp, value);
break;
default:
return "internal error: bad linked variable type";
}
Tcl_DStringResult(interp, &savedResult);
return NULL;
}
/*
*----------------------------------------------------------------------
*
* StringValue --
*
* Converts the value of a C variable to a string for use in a
* Tcl variable to which it is linked.
*
* Results:
* The return value is a pointer
to a string that represents
* the value of the C variable given by linkPtr.
*
* Side effects:
* None.
*
*----------------------------------------------------------------------
*/
static char *
StringValue(linkPtr, buffer)
Link *linkPtr; /* Structure describing linked variable. */
char *buffer; /* Small buffer to use for converting
* values. Must have TCL_DOUBLE_SPACE
* bytes or more. */
{
char *p;
switch (linkPtr->type) {
case TCL_LINK_INT:
linkPtr->lastValue.i = *(int *)(linkPtr->addr);
TclFormatInt(buffer, linkPtr->lastValue.i);
return buffer;
case TCL_LINK_DOUBLE:
linkPtr->lastValue.d = *(double *)(linkPtr->addr);
Tcl_PrintDouble((Tcl_Interp *) NULL, linkPtr->lastValue.d, buffer);
return buffer;
case TCL_LINK_BOOLEAN:
linkPtr->lastValue.i = *(int *)(linkPtr->addr);
if (linkPtr->lastValue.i != 0) {
return "1";
}
return "0";
case TCL_LINK_STRING:
p = *(char **)(linkPtr->addr);
if (p == NULL) {
return "NULL";
}
return p;
}
/*
* This code only gets executed if the link type is unknown
* (shouldn't ever happen).
*/
return "??";
}