I read all I could find about memory management in the Tcl API, but haven't been able to solve my problem so far. I wrote a Tcl extension to access an existing application. It works, except for a serious issue: memory leak.
I tried to reproduce the problem with minimal code, which you can find at the end of the post. The extension defines a new command, recordings, in namespace vtcl. The recordings command creates a list of 10000 elements, each element being a new command. Each command has data attached to it, which is the name of a recording. The name subcommand of each command returns the name of the recording.
I run the following Tcl code with tclsh to reproduce the problem:
load libvtcl.so
for {set ii 0} {$ii < 1000} {incr ii} {
set recs [vtcl::recordings]
foreach r $recs {rename $r ""}
}
The line foreach r $recs {rename $r ""} deletes all the commands at each iteration, which frees the memory of the piece of data attached to each command (I can see that in gdb). I can also see in gdb that the reference count of variable recs goes to 0 at each iteration so that the contents of the list is freed. Nonetheless, I see the memory of the process running tclsh going up at each iteration.
I have no more idea what else I could try. Help will be greatly appreciated.
#include <stdio.h>
#include <string.h>
#include <tcl.h>
static void DecrementRefCount(ClientData cd);
static int ListRecordingsCmd(ClientData cd, Tcl_Interp *interp, int objc,
Tcl_Obj *CONST objv[]);
static int RecordingCmd(ClientData cd, Tcl_Interp *interp, int objc,
Tcl_Obj *CONST objv[]);
static void
DecrementRefCount(ClientData cd)
{
Tcl_Obj *obj = (Tcl_Obj *) cd;
Tcl_DecrRefCount(obj);
return;
}
static int
ListRecordingsCmd(ClientData cd, Tcl_Interp *interp, int objc,
Tcl_Obj *CONST objv[])
{
char name_buf[20];
Tcl_Obj *rec_list = Tcl_NewListObj(0, NULL);
for (int ii = 0; ii < 10000; ii++)
{
static int obj_id = 0;
Tcl_Obj *cmd;
Tcl_Obj *rec_name;
cmd = Tcl_NewStringObj ("rec", -1);
Tcl_AppendObjToObj (cmd, Tcl_NewIntObj (obj_id++));
rec_name = Tcl_NewStringObj ("DM", -1);
snprintf(name_buf, sizeof(name_buf), "%04d", ii);
Tcl_AppendStringsToObj(rec_name, name_buf, (char *) NULL);
Tcl_IncrRefCount(rec_name);
Tcl_CreateObjCommand (interp, Tcl_GetString (cmd), RecordingCmd,
(ClientData) rec_name, DecrementRefCount);
Tcl_ListObjAppendElement (interp, rec_list, cmd);
}
Tcl_SetObjResult (interp, rec_list);
return TCL_OK;
}
static int
RecordingCmd(ClientData cd, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[])
{
Tcl_Obj *rec_name = (Tcl_Obj *)cd;
char *subcmd;
subcmd = Tcl_GetString (objv[1]);
if (strcmp (subcmd, "name") == 0)
{
Tcl_SetObjResult (interp, rec_name);
}
else
{
Tcl_Obj *result = Tcl_NewStringObj ("", 0);
Tcl_AppendStringsToObj (result,
"bad command \"",
Tcl_GetString (objv[1]),
"\"",
(char *) NULL);
Tcl_SetObjResult (interp, result);
return TCL_ERROR;
}
return TCL_OK;
}
int
Vtcl_Init(Tcl_Interp *interp)
{
#ifdef USE_TCL_STUBS
if (Tcl_InitStubs(interp, "8.5", 0) == NULL) {
return TCL_ERROR;
}
#endif
if (Tcl_PkgProvide(interp, "vtcl", "0.0.1") != TCL_OK)
return TCL_ERROR;
Tcl_CreateNamespace(interp, "vtcl", (ClientData) NULL,
(Tcl_NamespaceDeleteProc *) NULL);
Tcl_CreateObjCommand(interp, "::vtcl::recordings", ListRecordingsCmd,
(ClientData) NULL, (Tcl_CmdDeleteProc *) NULL);
return TCL_OK;
}