[mythtv-commits] Ticket #3692: Memory leak in DVB DummyVideo code

[MythTV]

#3692: Memory leak in DVB DummyVideo code
-----------------------+----------------------------------------------------
 Reporter:  anonymous  |       Owner:  danielk
     Type:  defect     |      Status:  new    
 Priority:  minor      |   Milestone:  unknown
Component:  dvb        |     Version:  unknown
 Severity:  medium     |     Mlocked:  0      
-----------------------+----------------------------------------------------
 I originally posted this in #3317 but that ticket got closed without
 resolving my issue.  For well over 6 months now, I've noticed that the
 backend slowly increases its virtual memory footprint.  Which eventually
 leads to slowing the entire machine down (more-so on machines with small
 amounts of RAM and not enough swap.

 Digging into it with pmap, I found lots of these:

 {{{
 pmap -d `pidof mythbackend`
 ...
 a10de000       4 ----- 00000000a10de000 000:00000   [ anon ]
 a10df000    8188 rwx-- 00000000a10df000 000:00000   [ anon ]
 ...
 }}}

 (That's 8MB of anonymous memory for those playing along).
 And I noticed that the number of these went up everytime I changed a
 channel.

 An 8MB Anonymous page is just what you see when libpthread allocates a new
 stack when creating a thread, but after several channel changes, I was
 seeing lots more of these anonymous-memory entries than running threads.
 So I surmized that we weren't reclaiming the stack when a thread
 terminated.

 I wrote a utility (included) to track all thread creation and what memory
 it was associated with (just a wrapper around libpthread) and was able to
 use it to map pthread_create calls to stack allocations.

 Using this, I determined that each time dvbrecorder.cpp::StartDummyVideo
 was called, the number of anonymous memory entries would increase, and
 these were never being reclaimed.

 Simply adding a:

 {{{
 pthread_detach(_video_thread);
 }}}

 right after the pthread_create call (this could alternatively be done
 using attributes passed to pthread_create I suppose) allows the pthread
 stacks to be reclaimed once the thread terminates, and now myth no longer
 increases it's virtual memory footprint by 8MB every time a channel-change
 occurs.

-- 
Ticket URL: <http://svn.mythtv.org/trac/ticket/3692>
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