Call to ca_context_destroy results in "Unhandled C++ exception"

[Simon Rees <simon.rees@psi.ch>]

Hi everyone

I have recently run into a problem when trying to get
the CA client library (from EPICS relase 3.14.9) going
on a VxWorks6.4 (mv5100) platform.

I run through the normal sequence of creating a context,
searching for the channel of interest, getting a value.
This all works fine and I can sit in a loop for hours
periodically printing out a value...

Then I try to close things down. First I destroy the
channel via 'ca_clear_channel'. This returns normal
status. It's the subsequent call to 'ca_context_destroy'
that has the problem. This results in the following
message being printed on the console:

   "Unhandled C++ exception resulted in call to terminate"


Here's what I have done in (so far fruitless) attempts
to resolve the problem:

1. I thought it might be something to do with the priority of
   the kernel task that runs the shell relative to that of the
   tasks that handle the network so I tried running my test
   function in a low priority task spawned from the shell.
   No improvement.

2. Initially I used the ca_disable_preemptive_callback
   threading model. I tried the preemptive threading
   model instead. No improvement.

3. I rebuilt the CA library with debug symbols enabled. I then
   fired up the Windriver workbench and delved into the call
   into the CA client code. Execution proceeded normally in
   the ca_context_destroy_code until the point marked
   "OUCH" !

      void epicsShareAPI ca_context_destroy ()
      {
         ca_client_context *pcac;
         if ( caClientContextId != NULL ) {
            pcac = (ca_client_context *) epicsThreadPrivateGet
            ( caClientContextId );
            if ( pcac )
            {
               delete pcac;  // <---- OUCH !!
               epicsThreadPrivateSet ( caClientContextId, 0 );
            }
         }
      }

   I followed the call into the ca_client_context destructor
   and did identify the line there that was causing the problem.
   But presumably the problem occurs due to my usage of the
   library or the way I have built it.

4. I have examined the options I used for building the library
   but nothing jumps out at me.


I am attaching my test code together with the test journal.

Many thanks for any suggesions - I am probably missing something
obvious !

Simon Rees
PSI Controls Group

#include "cadef.h"
#include <stdio.h>

/* Note: the type of an EPICS motor .RVAL field is DBF_LONG */
#define MY_TEST_PV  "PTEST-NCS-SC22:MOTOR.RVAL"

void simon_ca_test()
{
   chid myID;
   long value;
   int status;

   printf( "\n\nChannel access test function starting...\n\n");

   /* Initialise the context */
   printf( "Calling 'ca_context_create'... ");
   status = ca_context_create( ca_enable_preemptive_callback );
   if ( status != ECA_NORMAL )
   {
      printf( "\nERROR: call to 'ca_context_create' failed'\n\n" );
      return;
   }
   printf( "ok.\n");

   /* Buffer a create channel request */
   printf( "Calling 'ca_create_channel'... ");
   status = ca_create_channel ( MY_TEST_PV, NULL, NULL, CA_PRIORITY_DEFAULT, &myID );
   if ( status != ECA_NORMAL )
   {
      printf( "\nERROR: call to 'ca_create_channel' failed'\n\n" );
      return;
   }
   printf( "ok.\n");

   /* Send create channel request to network*/
   printf( "Calling 'ca_pend_io'... ");
   status = ca_pend_io( 5.0 );
   if ( status != ECA_NORMAL )
   {
      printf( "\nERROR: call to 'ca_pend_io' failed'\n\n" );
      return;
   }
   printf( "ok.\n");

   /* Buffer a get value request. */
   printf( "Calling 'ca_get'... ");
   ca_get( DBR_LONG, myID, &value );
   printf( "ok.\n");

   /* Send get value request to network */
   printf( "Calling 'ca_pend_io'... ");
   status = ca_pend_io( 5.0 );
   if ( status != ECA_NORMAL )
   {
      printf( "\nERROR: call to 'ca_pend_io' failed'\n\n" );
      return;
   }
   printf( "ok.\n");

   /* Display received value */
   printf( "Returned value was: %d\n", value );

   /* Clear down the channel */
   printf( "Calling 'ca_clear_channel'... ");
   status = ca_clear_channel( myID );
   if ( status != ECA_NORMAL )
   {
      printf( "\nERROR: call to 'ca_clear_channel' failed'\n\n" );
      return;
   }
   printf( "ok.\n");


   /* Destroy the context */
   printf( "Calling 'ca_context_destroy'... \n\n");
   ca_context_destroy();
   printf( "ok.\n\n");

   /* Print test successful message */
   printf( "Test completed ok.\n\n" );

} // simon_ca_test


-> 
-> sp simon_ca_test 
Task spawned: id = 0x2523e20, name = t5
value = 38944288 = 0x2523e20
-> 

Channel access test function starting...

Calling 'ca_context_create'... ok.
Calling 'ca_create_channel'... ok.
Calling 'ca_pend_io'... ok.
Calling 'ca_get'... ok.
Calling 'ca_pend_io'... ok.
Returned value was: 1234
Calling 'ca_clear_channel'... ok.
Calling 'ca_context_destroy'... 

0x2523e20 (t5): Unhandled C++ exception resulted in call to terminate