Re: Help with map driver

When you create a new player_map_data_t variable, the "data" pointer will always point to an invalid memory space until you allocate memory for it (or set it equal to another pointer that's already allocated.)  If you have your player_map_data_t at the class level, you can get away with allocating data once, but if you need to change the size of the data array you'll have to free and reallocate it.  Gridmap creates a new player_map_data_t for each map request, and handles allocating, using, and freeing the memory properly.

The queue overflow is happening because you're not calling Read() fast enough.  Messages are being published from the Player server and landing in your PlayerClient's message queue.  Read() will take information out of the message queue and copy it into the appropriate proxies.  You can call Read() or ReadIfWaiting() more often to solve this.  You can also use SetReplaceRule on one or more of your client proxies; setting the replace rule to true will cause new messages to overwrite older messages in the message queue, instead of queuing them up.

All of the libplayerc++ features and functions are outlined in the documentation online at http://playerstage.sourceforge.net/doc/Player-svn/player/group__player__clientlib__cplusplus.html  I find it useful to refer to when I'm wondering about how a particular proxy works.


Rich 

-----Original Message-----
From: aneves [mailto:[email protected]] 
Sent: Monday, August 30, 2010 1:09 PM
To: [email protected]
Subject: Re: [Playerstage-developers] 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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