snmp_sess_synch_response and thread safety

I am struggling to get snmp_sess_synch_response to work correctly from
multiple threads and am experiencing STAT_TIMEOUT errors when
attempting to perform an SNMP GET to multiple IP addresses
simultaneously.  I am using v5.4 of Net-SNMP on Linux (Ubuntu 6.10).
Here is the code, stripped of error checking for brevity:

...
// Calls _init_snmp, which won't then be called again
init_snmp("snmpapp");
// Create the threads
for (int i = 1; i <= 255; i++)
   create_thread();
...

Here is the thread function.  Assume that 'host' is a unique IP
address and oid_name the OID:

void fn(const char* ip, const char* oid_name)
{
  netsnmp_session session;
  snmp_sess_init(&session_);
  session.peername = ip;
  session.community = "public";
  session.community_len = strlen(session.community);
  void* ssp = snmp_sess_open(&session);
  netsnmp_session* ss = snmp_sess_session(ssp);
  ss->version = SNMP_VERSION_1;
  struct snmp_pdu *pdu = snmp_pdu_create(SNMP_MSG_GET);
  oid anOID[MAX_OID_LEN];
  size_t anOID_len = MAX_OID_LEN;
  read_objid(oid_name, anOID, &anOID_len);
  snmp_add_null_var(pdu, anOID, anOID_len);
  struct snmp_pdu *response;
  int status = snmp_sess_synch_response(ssp, pdu, &response);
  // Always returns STAT_TIMEOUT!
  ...
  snmp_free_pdu(response);
  snmp_sess_close(ssp);
}

The problem seems to be with the call to 'snmp_sess_synch_response'.
If I wrap this call with a lock (boost::mutex), then the code works
fine (although very slowly obviously).  I have looked at the source
but cannot see any obvious shared resources that could be getting
reset by each call.

This code forms part of an snmpscan function which trawls a specified
subnet looking for printers.  I have tried different timeouts, but
with no luck.  Note that I am expecting some IPs to timeout, as they
won't be printers, but it seems to be that as soon as one thread has
caused snmp_sess_synch_response to timeout, all the other threads
follow suit.

I know I could give the async_response call a try, but it is overkill
for my needs so I really want to the get the sync call to work.

Anyone have any ideas?  FWIW the same code works OK on Windows.

Regards.

-------------------------------------------------------------------------
This SF.net email is sponsored by DB2 Express
Download DB2 Express C - the FREE version of DB2 express and take
control of your XML. No limits. Just data. Click to get it now.
http://sourceforge.net/powerbar/db2/
_______________________________________________
Net-snmp-users mailing list
[email protected]
Please see the following page to unsubscribe or change other options:
https://lists.sourceforge.net/lists/listinfo/net-snmp-users