[Mono-devel-list] Heads up: marshalling changes
Zoltan Varga
vargaz at gmail.com
Tue Sep 7 08:27:32 EDT 2004
Hi,
'ref IntPtr' means the unmanaged function will receive a pointer to a pointer,
similar to void** in C. Try without the 'ref' and it will probably work.
Zoltan
> private static extern IntPtr (ref IntPtr foo, int value);
On Tue, 07 Sep 2004 13:29:50 +0200, RUAUDEL Frédéric
<ruaudel at embl-grenoble.fr> wrote:
> Hi Zoltan,
>
> I have memory allocation problem with one of my mono project. But I
> didn't test it before because I made it with mono 1.0.1 directly. What I
> have is quite strange and could be related to what you are saying, so I
> decided to send it to you. Feel free to skip it if you think it is not
> relevant but any help will be welcome.
>
> I try to map the Net-SNMP library in order to be able to send some snmp
> request to a snmp agent with mono. So to avoid having to map all the
> SNMP structure I made a little wrapper library in C to hide all the
> structure internals. Then I map them using IntPtr data type.
>
> I have a function of the form :
>
> struct foo* get_struct_foo ();
>
> that I map like this :
>
> [DllImport ("my_wrapper_lib")]
> private static extern IntPtr get_struct_foo ();
>
> then I have a function that fill that structure :
>
> void fill_struct_foo (struct foo* foo, int value);
>
> that I map :
>
> [DllImport ("my_wrapper_lib")]
> private static extern IntPtr (ref IntPtr foo, int value);
>
> And when I ask the C library to print the value of the pointer, the
> pointer received in the second function is always 0x11 and the program
> finish with a null pointer exception. But I have another structure
> initialized the same way and it works well. Maybe, I made a mistake in
> the marshaling of my parameters, but I tried almost all the possibility
> and read all msdn doc about it, but nothing has worked.
>
> Here is the instruction to reproduce the problem and the output of my
> test program with the pointer address :
>
> I create it on an FC2 distribution with mono-all.zip of Sep 3rd (V1.0.1)
>
> you must have the following packages installed :
>
> net-snmp 5.1.x (+ devel package)
> libelf or elfutils-libelf (+ devel package)
>
> tar zxvf net_snmp_wrapper.tar.gz
> cd net_snmp_wrapper
> make all test
>
> then start your snmp agent (default config should works) :
>
> service snmpd start or /etc/init.d/snmpd start
>
> and test the wrapper lib with :
>
> LD_LIBRARY_PATH=. ./test_wrapper public
>
> where "public" is your community string (this is the default one on linux)
>
> the output should be like this :
>
> DEBUG - wsnmp_open(after) : 0x91fffd0
> DEBUG - wsnmp_check_opened_session(before) : 0x91fffd0
> DEBUG - wsnmp_pdu_create_get(after) : 0x80af590 - 160
> DEBUG - wsnmp_add_null_var(before) : 0x80af590 - 0xfef82430 : 1 - 9
> DEBUG - wsnmp_add_null_var(before) : 0x80af590 - 0xfef82430 : 1 - 9
> DEBUG - wsnmp_add_null_var(before) : 0x80af590 - 0xfef82430 : 1 - 9
> Name: .1.3.6.1.2.1.1.1.0 = SNMPv2-MIB::sysDescr.0 - Type : 4 - Value :
> STRING: Linux toto.toto.net 2.6.5-1.358 #1 Sat May 8 09:04:50 EDT 2004 i686
> Name: .1.3.6.1.2.1.1.6.0 = SNMPv2-MIB::sysLocation.0 - Type : 4 - Value
> : STRING: "Somewhere"
> Name: .1.3.6.1.2.1.1.3.0 = SNMPv2-MIB::sysUpTime.0 - Type : 5 - Value :
> Timeticks: (798) 0:00:07.98
>
> Then compile the mono project
>
> tar zxvf net-snmp-sharp.tar.gz
> cd net-snmp-sharp
> export LD_LIBRARY_PATH=../net_snmp_wrapper
> make -f Makefile.net-snmp-sharp
> cp net-snmp-sharp.dll bin/Debug/
> cd test
> make -f Makefile.net-snmp-test
>
> then execute the test program :
>
> mono net-snmp-test.exe
>
> the output for me is :
>
> Hello World!
> DEBUG - wsnmp_open(after) : 0x8fd1ef0
> DEBUG - wsnmp_check_opened_session(before) : 0x8fd1ef0
> DEBUG - wsnmp_pdu_create_get(after) : 0x9019000 - 160
> DEBUG - wsnmp_add_null_var(before) : 0x11 - 0xf675782c : 1 - 9
>
> Unhandled Exception: System.NullReferenceException: Object reference not
> set to an instance of an object
> in (unmanaged) (wrapper managed-to-native) NetSnmp:wsnmp_add_null_var
> (intptr&,long[]&,int)
> in <0x00004> (wrapper managed-to-native) NetSnmp:wsnmp_add_null_var
> (intptr&,long[]&,int)
> in <0x0013b> NetSnmp:.ctor (string,string,string)
>
> the problem is that the pointer I retrieve with the function
> wsnmp_pdu_create_get (0x9019000) is lost when I send it to the function
> wsnmp_add_null_var(0x11). If you compare with the output of the C test
> function, you will see that the pointer remain the same (0x80af590). And
> it works well for the function wsnmp_open, the pointer remain the same
> in the function wsnmp_check_opened_session (0x8fd1ef0)
>
> the function declaration are the following :
>
> C: netsnmp_pdu* wsnmp_pdu_create_get (void);
> C#: private static extern IntPtr wsnmp_pdu_create_get ();
>
> C: netsnmp_variable_list* wsnmp_add_null_var (netsnmp_pdu* pdu,
> const oid* objid, size_t objid_len);
> C#: private static extern IntPtr wsnmp_add_null_var (ref IntPtr pdu,
> ref long[] objid, int objid_len);
>
> If you need more information, feel free to ask,
>
> Thanks in advance for any help on this,
>
> Fred
>
>
>
> Zoltan Varga wrote:
>
> > Hi,
> >
> > I checked in some major changes to mono's marshalling infrastructure primary
> >to fix some memory leaks with the old code. There is a high probability that
> >some things were broken in the process. So if you have some pinvoke code which
> >used to work but doesn't work now, drop a mail to the list, and I will
> >look into it.
> >
> > Zoltan
> >_______________________________________________
> >Mono-devel-list mailing list
> >Mono-devel-list at lists.ximian.com
> >http://lists.ximian.com/mailman/listinfo/mono-devel-list
> >
> >
> >
>
>
>
>
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