[zeromq-dev] Possibly a memleak in zframe_new()

[Pieter Hintjens]

zmsg_pop gives you a frame you have to destroy. Instead of

zframe_strdup (zmsg_pop())

use

zmsg_popstr ()

-Pieter

On Thu, Sep 19, 2013 at 3:08 PM, Yauheni Baltouski <ybaltouski at gmail.com> wrote:
> Hi Mathias,
>
> According to CZMQ manual, construction like
> char *msgData = zframe_strdup(zmsg_pop(m));
> zframe_t *frame = zmsg_pop(m);
>
> will return frame from message m and caller own this frame.
> So you need to zframe_destroy(&frame) after you call zframe_strdup()
> as it creates copy of
> string in frame and you release only this copy mem, not zframe.
>
> 2013/9/19 Mathias Hablützel <habl at zhaw.ch>:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> Hi everyone,
>>
>> ran into a situation where my code seems to leak memory but I can't
>> tackle it down in _my_ code. Kicked off valgrind to find this:
>>
>> ==2874== 56 bytes in 1 blocks are definitely lost in loss record 34 of 72
>> ==2874==    at 0x4A08121: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
>> ==2874==    by 0x4E7A968: zframe_new (czmq_prelude.h:443)
>> ==2874==    by 0x4E7AB48: zframe_recv (zframe.c:156)
>> ==2874==    by 0x4E7ED84: zmsg_recv (zmsg.c:101)
>> ==2874==    by 0x401458: _recv_message (kt_server.c:114)
>>
>> _recv_message() is my function, snippet:
>>
>>   zmsg_t *m = zmsg_recv(sock);
>>   assert(m);
>>   char *msgData = zframe_strdup(zmsg_pop(m));
>>   zmsg_destroy(&m);
>>   free (msgData);
>>
>>
>> So, I tracked this further down to zframe_new() which actually allocates
>> sizeof(zframe_t) and later passes this to zmq_msg_init(). Since I work
>> with a ZMQ_REP socket here, this must be in zmq::router_t::xrecv or more
>> precisely in fq.recvpipe. recvpipe then calls zmq::msg_t::close.
>>
>> And this is where I suspect the memory leak to happen. The union-struct
>> u defined in msg.hpp seems not to be freed correctly. But all this is
>> massive speculation from my side — mostly because I'm just a
>> beginner/noob and I have no clue about libzmq nor about C++.
>>
>> Let me know if I'm just a noob with no clue or I found something. :)
>>
>> Happy Hacking
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