Nim memory growth

clib.nim

import strformat
import strutils
import sequtils

echo "clib initialized"
echo GC_getStatistics()

proc hello_echo*(message:cstring):cstring {.exportc.} =
  ## Echo a message back
  var s_message:string = $message
  result = &"{s_message} echo"
  # echo &"Nim echo result: {result}"
  
proc stats*() {.exportc.} =
  echo GC_getStatistics()

Makefile

NIMBASE = ~/lib/Nim/lib/nimbase.h

.PHONY: run clean

run: a.out
	./a.out

a.out: test.cpp csrc/clib.cpp csrc/nimbase.h
	clang++ -Icsrc csrc/*.cpp test.cpp

csrc/clib.cpp: clib.nim
	mkdir -p csrc
	nim cpp --genScript --checks:on -d:traceGC --memTracker:on -d:memProfiler -d:lineDir -d:leakDetector -d:useSysAssert -d:useGcAssert --header --nimcache:csrc --noMain --compileOnly ./clib.nim

csrc/nimbase.h: $(NIMBASE) csrc/clib.cpp
	cp $(NIMBASE) csrc/nimbase.h

clean:
	-rm a.out
	-rm -r csrc

output.txt

clang++ -Icsrc csrc/*.cpp test.cpp
./a.out
clib initialized
[GC] total memory: 528384
[GC] occupied memory: 61528
[GC] stack scans: 0
[GC] stack cells: 0
[GC] cycle collections: 0
[GC] max threshold: 0
[GC] zct capacity: 1024
[GC] max cycle table size: 0
[GC] max pause time [ms]: 0
[GC] stack bottom: 0x7fff5bbaaec8
[GC] max stack size: 0

Hello world
C++ passing message: Hello 
C++ message addr: 0x7fff5bbaaf19
C++ retval addr : 0x1040f3158
Got reply: Hello  echo
C++ passing message: Hello -
C++ message addr: 0x7fff5bbaaf19
C++ retval addr : 0x1040f31a8
Got reply: Hello - echo

-- snip --

C++ message addr: 0x7fc75b002800
C++ retval addr : 0x105124050
Got reply: Hello --- (snip)
[GC] total memory: 22351872
[GC] occupied memory: 254440
[GC] stack scans: 86
[GC] stack cells: 10
[GC] cycle collections: 0
[GC] max threshold: 0
[GC] zct capacity: 1024
[GC] max cycle table size: 0
[GC] max pause time [ms]: 0
[GC] stack bottom: 0x7fff5bbaaec8
[GC] max stack size: 944

test.cpp

#include <iostream>
#include "csrc/clib.h"
using namespace std;

N_CDECL(void, NimMain)(void);

std::string echo(std::string arg) {
    const char* message = arg.c_str();
    cout << "C++ passing message: " << message << "\n";
    cout << "C++ message addr: " << (void*)message << "\n";
    char* retval = hello_echo(
        (char *)(message)
    );
    cout << "C++ retval addr : " << (void*)retval << "\n";
    return std::string(retval);
}

int main(void) {
    NimMain();
    cout << "Hello world\n";
    int i = 0;
    for (i = 0; i < 10000; i++) {
        std::string msg = "Hello " + std::string(i, '-');
        std::string ret = echo(msg);
        cout << "Got reply: " << ret << "\n";
    }
    stats();
    return 0;
}