CODEWITHSUNDEEP
c++valgrind
eltonsky
eltonsky

Reputation: 367

use signal handler to release resources?

I wrote a socket server. And I realize when I hit Ctrl-C while it's running, there's some possible memory leak. I used valgrind to find this.

My server code is quite simple. Basically I create a Listener object, start a thread to accept connections and try to join that thread:

 try {
    Server::Listener listener(1234);

    boost::thread l(boost::bind(&Server::Listener::start, &listener));

    l.join();

} catch(exception& e) {
    cout<<e.what()<<endl;
}

When I run valgrind, it give me:

==3580== Command: bin/Debug/p_rpc
==3580==
Listner started ...
in loop..
^C==3580==
==3580== HEAP SUMMARY:
==3580== in use at exit: 3,176 bytes in 24 blocks
==3580== total heap usage: 28 allocs, 4 frees, 4,328 bytes allocated
==3580==
==3580== 288 bytes in 1 blocks are possibly lost in loss record 21 of 24
==3580== at 0x4C29E46: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3580== by 0x4012084: _dl_allocate_tls (dl-tls.c:297)
==3580== by 0x4E3AABC: pthread_create@@GLIBC_2.2.5 (allocatestack.c:571)
==3580== by 0x5260F9F: boost::thread::start_thread() (in
/usr/lib/libboost_thread.so.1.49.0) ==3580== by 0x407B93: boost::thread::thread, boost::_bi::list1 > > >(boost::_bi::bind_t, boost::_bi::list1 > >&&) (thread.hpp:171)
==3580== by 0x404CA4: main (main.cpp:179)
==3580==
==3580== LEAK SUMMARY:
==3580== definitely lost: 0 bytes in 0 blocks
==3580== indirectly lost: 0 bytes in 0 blocks
==3580== possibly lost: 288 bytes in 1 blocks
==3580== still reachable: 2,888 bytes in 23 blocks
==3580== suppressed: 0 bytes in 0 blocks
==3580== Reachable blocks (those to which a pointer was found) are not shown.
==3580== To see them, rerun with: --leak-check=full --show-reachable=yes
==3580==
==3580== For counts of detected and suppressed errors, rerun with: -v
==3580== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 2 from 2)
Killed

It points out there's 288bytes possibly lost. I imagine I could use a signal handler to release this resourse. But I don't know how I do that. Can you give me an example please?

Cheers, Elton

Upvotes: 0

Views: 526

Answers (2)

vonbrand
vonbrand

Reputation: 11831

In principle, you can destroy the object there. There are restrictions on what you can do in a signal handler, and they mix very badly with threads. Note that in this area the compiler can do no (or very little) checking, the signal handler is just an ordinary function. Be extra careful.

The answers to this question give some details on how to do it.

Upvotes: 1

Matt Kline
Matt Kline

Reputation: 10507

When a process closes, the OS automatically cleans up all memory owned by the process. You don't need to worry about freeing that memory when the program exits. The building is being demolished. Don't bother sweeping the floor and emptying the trash cans and erasing the whiteboards. And don't line up at the exit to the building so everybody can move their in/out magnet to out. All you're doing is making the demolition team wait for you to finish these pointless housecleaning tasks.

The kind of leaks you do need to worry about are those that continuously leak during the program's lifetime.

Upvotes: 2

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