Re: Help with map driver

Hi Rich!

Thanks a lot. You solved my problem. The problem was the lack of
RequestMap(). I never used the MapProxy before :blush:.

 For now i'm not having problems with the allocation but i'll do what you
say. If I understood right it's only a matter of time untill the pointer
points randomly to a forbiden section of the memory.

Now i'm having some queue overflow after the program is running for a while.
"playerc error   : queue overflow; discarding packets"

Any ideas why?

Thnaks once again. you are saving my life:)


  

Rich Mattes-2 wrote:
> 
> I just checked the gridmap driver in svn, it is using "new" to allocate
> the data array: mapresp->data = new int8_t [mapresp->data_count];
> 
> In the map data structure, the "data" field is declared pointer to a
> double, as opposed to the other values which are declared directly.  When
> you initialize a player_map_data_t, all of the other fields have a value,
> but the pointer "data" is pointing at a random section of memory.  If you
> don't allocate it using either "new" or "malloc", any attempt to write to
> the variable is going to cause a segmentation violation (which is a memory
> access error).  Make sure you create the data variable before writing to
> it, and then de-allocate it (with delete or free) after you publish it.
> 
> As far as your client program, it looks like it's breaking at the
> GetCell() command.  You need to use RequestMap() to fill in the map data
> before you try to access any of the map data.  If the underlying driver
> doesn't respond properly to RequestMap, that might also cause a failure.
> 
> Rich
> 
> -----Original Message-----
> From: aneves [mailto:[email protected]] 
> Sent: Monday, August 30, 2010 9:56 AM
> To: [email protected]
> Subject: Re: [Playerstage-developers] Help with map driver
> 
> 
> 
> 
> Rich Mattes-2 wrote:
>> 
>> Have you tried using gdb on your driver?  make sure that your plugin is
>> compiled with the -g option, then run
>> 
> 
> now is my client program that's faulting here's the gdb output from him:
> 
> neves@neves:~/code/driver/test_client$ gdb ./loa
> GNU gdb (GDB) 7.1-ubuntu
> Copyright (C) 2010 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later
> <http://gnu.org/licenses/gpl.html>
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
> and "show warranty" for details.
> This GDB was configured as "i486-linux-gnu".
> For bug reporting instructions, please see:
> <http://www.gnu.org/software/gdb/bugs/>...
> Lendo símbolos de /home/neves/code/driver/test_client/loa...concluído.
> (gdb) run
> Starting program: /home/neves/code/driver/test_client/loa 
> [Thread debugging using libthread_db enabled]
> calling connect
> done
> minR: 1e+09     minL: 1e+09
> 
> 
> Program received signal SIGSEGV, Segmentation fault.
> 0x080498d3 in PlayerCc::ClientProxy::GetVar<char> (argc=1,
> argv=0xbffff3a4)
> at /usr/include/player-2.0/libplayerc++/clientproxy.h:116
> 116           T v = aV;
> (gdb) bt
> #0  0x080498d3 in PlayerCc::ClientProxy::GetVar<char> (argc=1,
> argv=0xbffff3a4) at /usr/include/player-2.0/libplayerc++/clientproxy.h:116
> #1  PlayerCc::MapProxy::GetCell (argc=1, argv=0xbffff3a4) at
> /usr/include/player-2.0/libplayerc++/playerc++.h:1219
> #2  main (argc=1, argv=0xbffff3a4) at laserobstacleavoid.cc:80
> (gdb) list
> 111         // c library to make sure the data access is thread safe.
> 112         template<typename T>
> 113         T GetVar(const T &aV) const
> 114         { // these have to be defined here since they're templates
> 115           scoped_lock_t lock(mPc->mMutex);
> 116           T v = aV;
> 117           return v;
> 118         }
> 119
> 120         // @brief Get a variable from the client by reference
>  
> 
> 
> 
> 
>> Once the program segfaults, use the 'bt' and 'list' commands to determine
>> where your program was when it crashed.  The below code snippet isn't
>> enough
>> to tell the whole story, but are you allocating map_data.data before you
>> attempt to write to it?  You should allocate it with the "new" keyword or
>> with "malloc".
>> 
>> Rich
>> 
> 
> I'm not using "malloc" nor "new". I just copied this part from the gridmap
> driver and it too doesn't use "malloc" or "new".
> I'm really lost!
> 
> thanks for your help ,
> 
> andré 
> 
> 
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> 
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