[systemd-devel] SD-Bus: Possible bug / lack of documentation causing memory leak (at exit?)

[Pauli Sundberg]

Hi!

I stumbled upon a memory leak with attached silly test program (attached
below), and while doing some testing i found out that i need to call the
'sd_bus_process' after
'sd_bus_release_name' to avoid memory leak

The leak shows up with valgrind, and looks like
==18842== 3,402 (1,800 direct, 1,602 indirect) bytes in 1 blocks are
definitely lost in loss record 11 of 12
==18842==    at 0x4C31B25: calloc (in /usr/lib/valgrind/vgpreload_
memcheck-amd64-linux.so)
==18842==    by 0x4E8AC2F: sd_bus_new (sd-bus.c:177)
==18842==    by 0x4E8E5C1: sd_bus_open_user (sd-bus.c:1138)
==18842==    by 0x108D47: Component::dbus_open() (in /XXX/sdtest)
==18842==    by 0x108BCC: main (in /XXX/sdtest)


On the appendix there is the 'FIXME' marker with line that makes the memory
leak go away.

Is this lack of documentation or a bug? I found the issue with stock ubuntu
17.04 version -  234-2ubuntu12.1 -- and recompiled current git head
82a18dcfb23fe5f259a2eb555fb90e3a3475f12d and the issue seems to be in both
versions.

I was about to do man-page pull request, but started to hesitate, since the
code in the release looks like such that it would handle some messaging.


Cheers,
Pauli




=== Appendix A: test program ===

#include <stdio.h>
#include <stdlib.h>
#include <systemd/sd-bus.h>
#include <assert.h>

class Component
{
public:
Component(  const char* name ) : dbus( NULL )
{
   this->name = name;
}


~Component()
{
  if ( this->dbus )
  {
     printf("Destructor called!\n");
     assert( sd_bus_release_name( dbus, this->name ) >= 0 );

     loop(); // FIXME: Commenting this makes it leak memory
     sd_bus_flush(dbus);
     sd_bus_unref(dbus);
  }
}


  bool loop()
  {
      for ( ;; )
      {
         int ret =   sd_bus_process( dbus, NULL);
         assert ( ret >= 0 );

         if ( ret > 0 )
             continue;

         break;
      }
      return true;
  }

  bool dbus_open()
  {
      int r;
      r = sd_bus_open_user(&dbus);
      if (r < 0)
      {
         printf( "Failed to connect to system bus: %s\n", strerror(-r) );
         return false;
      }


      // Take a well-known service name so that clients can find us
      r = sd_bus_request_name(dbus, this->name , 0);
      if (r < 0)
      {
        printf("Failed to acquire service name: %s\n", strerror(-r));
        return false;
      }

      return true;
  }

private:
    sd_bus* dbus;
    const char* name;
};


int main()
{
    Component com{ "com.example.foobar" };
    printf("Hello there!\n");
    com.dbus_open();
    com.loop();
    printf("Bye then!\n");
}
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