7

I have code which embeds a tcl interpreter in my c++ program. When running with valgrind it shows a bunch of possible memory leaks from the TCL interpreter. I am using Tcl_DeleteInterp(interp); to clean up the interpreter before exiting the program. I'm curious if these leaks should be worried about or not.

Main file:

#include <tcl.h>

int main(int argc, char* argv[]) {

    // Initialize Tcl interpreter
    Tcl_Interp* interp = Tcl_CreateInterp();
    // Clean up Tcl interpreter
    Tcl_DeleteInterp(interp);

    return 0;
}

Compilation Command: g++ -g main2.cpp -o test -ltcl

Valgrind Command: valgrind --tool=memcheck --log-file=memcheck.txt --leak-check=full --verbose --track-origins=yes ./test

Valgrind Output:

--2365686-- Valgrind options:
--2365686--    --tool=memcheck
--2365686--    --log-file=memcheck.txt
--2365686--    --leak-check=full
--2365686--    --verbose
--2365686--    --track-origins=yes
--2365686-- Contents of /proc/version:
--2365686--   Linux version 4.18.0-553.44.1.el8_10.x86_64 ([email protected]) (gcc version 8.5.0 20210514 (Red Hat 8.5.0-24) (GCC)) #1 SMP Wed Mar 5 10:48:41 EST 2025
--2365686-- 
--2365686-- Arch and hwcaps: AMD64, LittleEndian, amd64-cx16-lzcnt-rdtscp-sse3-ssse3-avx-avx2-bmi-f16c-rdrand-rdseed
--2365686-- Page sizes: currently 4096, max supported 4096
--2365686-- Valgrind library directory: /usr/libexec/valgrind
--2365686-- Reading syms from ~/test
--2365686-- Reading syms from /usr/lib64/ld-2.28.so
--2365686-- Warning: cross-CU LIMITATION: some inlined fn names
--2365686-- might be shown as UnknownInlinedFun
--2365686-- Reading syms from /usr/libexec/valgrind/memcheck-amd64-linux
--2365686--    object doesn't have a dynamic symbol table
--2365686-- Scheduler: using generic scheduler lock implementation.
--2365686-- Reading suppressions file: /usr/libexec/valgrind/default.supp
==2365686== embedded gdbserver: reading from /tmp/vgdb-pipe-from-vgdb-to-2365686-by-user
==2365686== embedded gdbserver: writing to   /tmp/vgdb-pipe-to-vgdb-from-2365686-by-user
==2365686== embedded gdbserver: shared mem   /tmp/vgdb-pipe-shared-mem-vgdb-2365686-by-user
==2365686== 
==2365686== TO CONTROL THIS PROCESS USING vgdb (which you probably
==2365686== don't want to do, unless you know exactly what you're doing,
==2365686== or are doing some strange experiment):
==2365686==   /usr/libexec/valgrind/../../bin/vgdb --pid=2365686 ...command...
==2365686== 
==2365686== TO DEBUG THIS PROCESS USING GDB: start GDB like this
==2365686==   /path/to/gdb ./test
==2365686== and then give GDB the following command
==2365686==   target remote | /usr/libexec/valgrind/../../bin/vgdb --pid=2365686
==2365686== --pid is optional if only one valgrind process is running
==2365686== 
--2365686-- REDIR: 0x4004400 (ld-linux-x86-64.so.2:strlen) redirected to 0x580d2e42 (???)
--2365686-- REDIR: 0x4002d80 (ld-linux-x86-64.so.2:index) redirected to 0x580d2e5c (???)
--2365686-- Reading syms from /usr/libexec/valgrind/vgpreload_core-amd64-linux.so
--2365686-- Reading syms from /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so
==2365686== WARNING: new redirection conflicts with existing -- ignoring it
--2365686--     old: 0x04004400 (strlen              ) R-> (0000.0) 0x580d2e42 ???
--2365686--     new: 0x04004400 (strlen              ) R-> (2007.0) 0x04c42300 strlen
--2365686-- REDIR: 0x4002fb0 (ld-linux-x86-64.so.2:strcmp) redirected to 0x4c434c0 (strcmp)
--2365686-- REDIR: 0x4002760 (ld-linux-x86-64.so.2:mempcpy) redirected to 0x4c46ff0 (mempcpy)
--2365686-- Reading syms from /usr/lib64/libtcl8.6.so
--2365686-- Reading syms from /usr/lib64/libstdc++.so.6.0.25
--2365686-- Reading syms from /usr/lib64/libm-2.28.so
--2365686-- Reading syms from /usr/lib64/libgcc_s-8-20210514.so.1
--2365686-- Reading syms from /usr/lib64/libc-2.28.so
==2365686== WARNING: new redirection conflicts with existing -- ignoring it
--2365686--     old: 0x05bd8f50 (memalign            ) R-> (1011.0) 0x04c40d9e memalign
--2365686--     new: 0x05bd8f50 (memalign            ) R-> (1017.0) 0x04c41527 aligned_alloc
==2365686== WARNING: new redirection conflicts with existing -- ignoring it
--2365686--     old: 0x05bd8f50 (memalign            ) R-> (1011.0) 0x04c40d9e memalign
--2365686--     new: 0x05bd8f50 (memalign            ) R-> (1017.0) 0x04c413bd aligned_alloc
==2365686== WARNING: new redirection conflicts with existing -- ignoring it
--2365686--     old: 0x05bd8f50 (memalign            ) R-> (1011.0) 0x04c40d9e memalign
--2365686--     new: 0x05bd8f50 (memalign            ) R-> (1017.0) 0x04c41527 aligned_alloc
==2365686== WARNING: new redirection conflicts with existing -- ignoring it
--2365686--     old: 0x05bd8f50 (memalign            ) R-> (1011.0) 0x04c40d9e memalign
--2365686--     new: 0x05bd8f50 (memalign            ) R-> (1017.0) 0x04c413bd aligned_alloc
==2365686== WARNING: new redirection conflicts with existing -- ignoring it
--2365686--     old: 0x05bd8f50 (memalign            ) R-> (1011.0) 0x04c40d9e memalign
--2365686--     new: 0x05bd8f50 (memalign            ) R-> (1017.0) 0x04c41527 aligned_alloc
==2365686== WARNING: new redirection conflicts with existing -- ignoring it
--2365686--     old: 0x05bd8f50 (memalign            ) R-> (1011.0) 0x04c40d9e memalign
--2365686--     new: 0x05bd8f50 (memalign            ) R-> (1017.0) 0x04c413bd aligned_alloc
--2365686-- Reading syms from /usr/lib64/libdl-2.28.so
--2365686-- Reading syms from /usr/lib64/libz.so.1.2.11
--2365686-- Reading syms from /usr/lib64/libpthread-2.28.so
--2365686-- REDIR: 0x5bdd460 (libc.so.6:memmove) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
==2365686== Preferring higher priority redirection:
--2365686--     old: 0x05be4800 (__memcpy_avx_unalign) R-> (2018.0) 0x04c44700 __memcpy_avx_unaligned_erms
--2365686--     new: 0x05be4800 (__memcpy_avx_unalign) R-> (2018.1) 0x04c46030 memmove
--2365686-- REDIR: 0x5bdc680 (libc.so.6:strncpy) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdda40 (libc.so.6:strcasecmp) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdbdf0 (libc.so.6:strcat) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdc710 (libc.so.6:rindex) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdf210 (libc.so.6:rawmemchr) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5c23420 (libc.so.6:wmemchr) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5c22d40 (libc.so.6:wcscmp) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdd690 (libc.so.6:mempcpy) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdd3c0 (libc.so.6:bcmp) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdc5e0 (libc.so.6:strncmp) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdbf00 (libc.so.6:strcmp) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdd590 (libc.so.6:memset) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5c22cc0 (libc.so.6:wcschr) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdc4d0 (libc.so.6:strnlen) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdc040 (libc.so.6:strcspn) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bddae0 (libc.so.6:strncasecmp) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdbfb0 (libc.so.6:strcpy) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bddd20 (libc.so.6:memcpy@@GLIBC_2.14) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5c247c0 (libc.so.6:wcsnlen) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdc790 (libc.so.6:strpbrk) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdbe80 (libc.so.6:index) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdc450 (libc.so.6:strlen) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5be3d80 (libc.so.6:memrchr) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bddb80 (libc.so.6:strcasecmp_l) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdd330 (libc.so.6:memchr) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5c22e90 (libc.so.6:wcslen) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdca50 (libc.so.6:strspn) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdd9b0 (libc.so.6:stpncpy) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdd920 (libc.so.6:stpcpy) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdf2a0 (libc.so.6:strchrnul) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bddc20 (libc.so.6:strncasecmp_l) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5c234b0 (libc.so.6:wmemcmp) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5c88cb0 (libc.so.6:__memcpy_chk) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5bdd250 (libc.so.6:strstr) redirected to 0x4a3277b (_vgnU_ifunc_wrapper)
--2365686-- REDIR: 0x5beaa30 (libc.so.6:__strrchr_avx2) redirected to 0x4c41c90 (rindex)
--2365686-- REDIR: 0x5bd81e0 (libc.so.6:malloc) redirected to 0x4c3910f (malloc)
--2365686-- REDIR: 0x5be77f0 (libc.so.6:__strcmp_avx2) redirected to 0x4c43380 (strcmp)
--2365686-- REDIR: 0x5be80e0 (libc.so.6:__strlen_avx2) redirected to 0x4c421e0 (strlen)
--2365686-- REDIR: 0x5be97b0 (libc.so.6:__strncmp_avx2) redirected to 0x4c42990 (strncmp)
--2365686-- REDIR: 0x5be4080 (libc.so.6:__memchr_avx2) redirected to 0x4c43560 (memchr)
--2365686-- REDIR: 0x5be73c0 (libc.so.6:__strchr_avx2) redirected to 0x4c41e70 (index)
--2365686-- REDIR: 0x5be7600 (libc.so.6:__strchrnul_avx2) redirected to 0x4c46b20 (strchrnul)
--2365686-- REDIR: 0x5be47e0 (libc.so.6:__mempcpy_avx_unaligned_erms) redirected to 0x4c46c30 (mempcpy)
--2365686-- REDIR: 0x5be4800 (libc.so.6:__memcpy_avx_unaligned_erms) redirected to 0x4c46030 (memmove)
--2365686-- REDIR: 0x5bd8870 (libc.so.6:free) redirected to 0x4c3c459 (free)
--2365686-- REDIR: 0x5be55f0 (libc.so.6:__stpcpy_avx2) redirected to 0x4c45840 (stpcpy)
--2365686-- REDIR: 0x5bd9010 (libc.so.6:calloc) redirected to 0x4c408d9 (calloc)
--2365686-- REDIR: 0x5be5340 (libc.so.6:__memset_avx2_unaligned_erms) redirected to 0x4c45f20 (memset)
--2365686-- REDIR: 0x5be7d50 (libc.so.6:__strcpy_avx2) redirected to 0x4c42330 (strcpy)
--2365686-- REDIR: 0x5be4360 (libc.so.6:__memcmp_avx2_movbe) redirected to 0x4c45700 (bcmp)
--2365686-- REDIR: 0x5b737e0 (libc.so.6:__strstr_sse2_unaligned) redirected to 0x4c47160 (strstr)
--2365686-- REDIR: 0x5c89210 (libc.so.6:__strcpy_chk) redirected to 0x4c46b90 (__strcpy_chk)
--2365686-- REDIR: 0x5bd8af0 (libc.so.6:realloc) redirected to 0x4c40af3 (realloc)
--2365686-- REDIR: 0x5bdcf60 (libc.so.6:__GI_strstr) redirected to 0x4c471d0 (__strstr_sse2)
--2365686-- REDIR: 0x5be8260 (libc.so.6:__strncasecmp_avx2) redirected to 0x4c42d10 (strncasecmp)
--2365686-- Reading syms from /usr/lib64/libnss_files-2.28.so
--2365686-- Reading syms from /usr/lib64/libnss_sss.so.2
--2365686-- Discarding syms at 0x139077b0-0x1390dd32 in /usr/lib64/libnss_files-2.28.so (have_dinfo 1)
--2365686-- Discarding syms at 0x13b19b80-0x13b20126 in /usr/lib64/libnss_sss.so.2 (have_dinfo 1)
==2365686== 
==2365686== HEAP SUMMARY:
==2365686==     in use at exit: 455,044 bytes in 41 blocks
==2365686==   total heap usage: 127 allocs, 86 frees, 546,384 bytes allocated
==2365686== 
==2365686== Searching for pointers to 41 not-freed blocks
==2365686== Checked 398,464 bytes
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 13 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F788CB: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F1A7F6: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94596: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 14 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F12C87: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F1A805: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94596: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 15 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F12CCA: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F1A805: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94596: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 16 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F7B93F: Tcl_GetThreadData (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F9EB39: Tcl_InitNotifier (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F5B763: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94596: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 17 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F586B6: Tcl_CreateNamespace (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F58DA8: TclGetNamespaceForQualName (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F59653: Tcl_FindNamespace (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F15CB3: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94D1E: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 18 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F586B6: Tcl_CreateNamespace (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F58DA8: TclGetNamespaceForQualName (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F59653: Tcl_FindNamespace (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F15CB3: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94D26: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 19 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F06741: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F30FC1: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F0761D: Tcl_DictObjPut (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F15DA2: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94D2E: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 20 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E8F8B1: Tcl_CreateObjCommand (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94562: Tcl_NRCreateCommand (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F15DDB: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94D2E: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 21 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F586B6: Tcl_CreateNamespace (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F58DA8: TclGetNamespaceForQualName (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F59653: Tcl_FindNamespace (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F15CB3: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94D36: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 22 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E8F8B1: Tcl_CreateObjCommand (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94562: Tcl_NRCreateCommand (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F15DDB: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94D3E: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 23 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F586B6: Tcl_CreateNamespace (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F58DA8: TclGetNamespaceForQualName (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F59653: Tcl_FindNamespace (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F15CB3: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94D46: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 24 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E8F8B1: Tcl_CreateObjCommand (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94EBE: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 25 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F7C48E: TclpRealloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E9999B: Tcl_Realloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F590A3: Tcl_Export (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94ECF: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 26 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F7B93F: Tcl_GetThreadData (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F9DFEF: TclpGetPwUid (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F9D487: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E950BF: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 27 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E8F8B1: Tcl_CreateObjCommand (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94562: Tcl_NRCreateCommand (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F15DDB: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4FB0707: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4FA0C31: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E95117: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 28 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F586B6: Tcl_CreateNamespace (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F9FC78: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4FA2AD7: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4FADEF1: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4FA0C39: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E95117: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 16,384 bytes in 1 blocks are possibly lost in loss record 29 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E998FB: Tcl_Alloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F732E7: Tcl_NewStringObj (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F626BC: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E92976: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E93206: Tcl_EvalEx (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E93228: Tcl_Eval (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4FA0C7E: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E95117: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 32,768 bytes in 2 blocks are possibly lost in loss record 30 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C119: TclpAlloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F7C48E: TclpRealloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E9999B: Tcl_Realloc (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F85E5E: Tcl_DStringSetLength (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F12EC0: Tcl_ExternalToUtfDString (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F18DC5: TclSetupEnv (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E94FBB: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 38,400 bytes in 1 blocks are possibly lost in loss record 31 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C653: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F5CD1C: Tcl_NewObj (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E945D1: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== 38,400 bytes in 1 blocks are possibly lost in loss record 32 of 32
==2365686==    at 0x4C39185: malloc (vg_replace_malloc.c:442)
==2365686==    by 0x4F7C653: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4F15E05: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4FB06F1: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4FA0C31: ??? (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4E95117: Tcl_CreateInterp (in /usr/lib64/libtcl8.6.so)
==2365686==    by 0x4006A9: main (main2.cpp:6)
==2365686== 
==2365686== LEAK SUMMARY:
==2365686==    definitely lost: 0 bytes in 0 blocks
==2365686==    indirectly lost: 0 bytes in 0 blocks
==2365686==      possibly lost: 388,096 bytes in 21 blocks
==2365686==    still reachable: 66,948 bytes in 20 blocks
==2365686==         suppressed: 0 bytes in 0 blocks
==2365686== Reachable blocks (those to which a pointer was found) are not shown.
==2365686== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==2365686== 
==2365686== ERROR SUMMARY: 20 errors from 20 contexts (suppressed: 0 from 0)
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13
  • 3
    int main() { Tcl_Interp* interp = Tcl_CreateInterp(); Tcl_DeleteInterp(interp); }-- You should start with only those two lines to see if this causes leaks. Then add lines until you see the leak messages. Also, I advise using RAII for things like this. What would happen if in a larger program, an exception thrown, and the Tcl_DeleteInterp(interp) is never executed? Commented Apr 6 at 1:35
  • 2
    my 2 kopeks - there are no 'hard' errors, just allocations that valgrind cannot accurately determine, and should be ignored. Also recommend adding Tcl_Finalize() to the example then rerun - this 'cleans' up the tcl environment [tcl-lang.org/man/tcl8.5/TclLib/Exit.html] Commented Apr 6 at 7:24
  • 1
    Frankly Tcl is being fairly crappy in this respect. From what I see it's so bad that in this example it's barely worth the bother of calling Tcl_DeleteInterp. There's not much that you can do about it. Commented Apr 6 at 8:58
  • 1
    @ticktalk Rubbish. "just allocations that valgrind cannot accurately determine". Valgrind gives the exact number of bytes and the hex address of the instruction that called the allocation function. In what way is that not accurate? OP needs to have debuginfo to get the source file names and line numbers. Commented Apr 6 at 9:05
  • 2
    The PURIFY flag is for compiling Tcl, not your application. If you wish to find actual memory leaks in the interpreter, you should compile it with TCL_MEM_DEBUG set as well. Commented Apr 6 at 17:33

2 Answers 2

Reset to default
5

Tcl maintains a number of in-memory caches of various things inside itself. These are not deleted when Tcl_DeleteInterp() is called because they are not bound to that interpreter (and you may have multiple interpreters in a process). These caches do not grow in size, but can be deleted by calling Tcl_Finalize(), which constitutes a promise that you will not be calling further Tcl API functions in the current process.

It's not normally called by tclsh on exit because that just slows the exiting for no real value; the OS cleans up the memory just fine and much faster. (Resources that need special cleanup, such as IO buffers, are handled correctly using atexit() callbacks.)

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1

If I add a call the Tcl_Finalize() then I get

==3082003== 688 bytes in 1 blocks are still reachable in loss record 1 of 24
==3082003==    at 0x4043EEF: calloc (vg_replace_malloc.c:1675)
==3082003==    by 0x4B6206E: ??? (in /usr/lib64/libtcl8.6.so)
==3082003==    by 0x4B62614: TclpFree (in /usr/lib64/libtcl8.6.so)
==3082003==    by 0x4B5ED43: ??? (in /usr/lib64/libtcl8.6.so)
==3082003==    by 0x4B00B55: Tcl_Finalize (in /usr/lib64/libtcl8.6.so)
==3082003==    by 0x40116E: main (lk2.cpp:10)

So even Tcl_Finalize() allocates something that it fails to deallocate.

And here are the two summaries, without Tcl_Finalize

==3226866== HEAP SUMMARY:
==3226866==     in use at exit: 438,660 bytes in 40 blocks
==3226866==   total heap usage: 43 allocs, 3 frees, 511,468 bytes allocated
...
==3159994== LEAK SUMMARY:
==3159994==    definitely lost: 0 bytes in 0 blocks
==3159994==    indirectly lost: 0 bytes in 0 blocks
==3159994==      possibly lost: 311,296 bytes in 19 blocks
==3159994==    still reachable: 127,364 bytes in 21 blocks
==3159994==         suppressed: 0 bytes in 0 blocks

With Tcl_Finalize

==3208034== HEAP SUMMARY:
==3208034==     in use at exit: 437,936 bytes in 25 blocks
==3208034==   total heap usage: 45 allocs, 20 frees, 512,844 bytes allocated
...
==3208034== LEAK SUMMARY:
==3208034==    definitely lost: 0 bytes in 0 blocks
==3208034==    indirectly lost: 0 bytes in 0 blocks
==3208034==      possibly lost: 196,608 bytes in 12 blocks
==3208034==    still reachable: 241,328 bytes in 13 blocks
==3208034==         suppressed: 0 bytes in 0 blocks

That's a net gain of 724 bytes and 15 blocks.

The main reason that it's a waste of time calling Tcl_Finalize is that it only deallocates 0.16% of the memory still in use at exit.

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