Throw/Raise Exception From Probes

You can raise and Ada exception or throw a C++ exception from a probe.

In Ada you will need to know the name of the exception you want to raise. This can be as simple as constraint_error or a more complex fully-qualified name pkg.child.my_exception.

In C++ you will have to provide: the exception object (usually referenced in the application program using a target expression, for example $MyExceptionObject), the exception typeinfo, a constructor, and a destructor. Below are some prototype macros which make this a little bit easier.

If you raise/throw and exception in an on_entry action of a probe, the function call will be stubbed and the exception will be raised/thrown when the probed function exits.

If you raise/throw and exception in an on_line/offset action of a probe, the exception will be raised/thrown at that point.

If you raise/throw and exception in an on_exit action of a probe, the exception will be raised/thrown when the function returns.

Ada Example

The Ada example demonstrates how to raise an Ada exception from a probe on_entry/on_line/on_exit action. Note that #ifdef's are used to condition the Aprobe macro used to raise the exception depending on the target compiler (PowerAda or Gnat).

#ifdef _AIX
#define RAISE ap_RaisePowerAdaException
#else
#define RAISE ap_RaiseGnatException
#endif

probe thread
{
   probe "tmain.x1" 
   {
      on_entry 
      {
         RAISE("constraint_error");
      }
   }

   probe "tmain.x2" 
   {
      on_exit 
      {
         RAISE("ada.io_exceptions.status_error");
      }
   }

   probe "tmain.x3" 
   {
      on_line(27) 
      {
         RAISE("my_exception");
      }
   }
}

C/C++ Example

Throwing C++ exceptions is more complicated. The file aprobe.h defines some macros to make the process easier: ap_ThrowwGccObject() and ap_ThrowGccString(). If the macros fail, you will have to extract the proper information yourself and call ap_ThrowGccException() directly.

//
// The example probe which uses the helper macros.
//
probe thread
{
   int count = 0;

   probe "service(int, int)"
   {
      on_entry
      {
         count++;
         if (count == 1)
         {
            // throw E;
            // E is the exception class and $e1 is the exception object declared in the application.
            ap_ThrowGccObject("E", $e1, ap_ApplicationModuleId());
         }
         else if (count == 2)
         {
            // throw myexception;
            // my exception is the exception class and $e2 is the exception object declared in the application.
            ap_ThrowGccObject("myexception", $e2, ap_ApplicationModuleId());
         }
         else
         {
            // throw "Exception";
            // throw a local string object.
            ap_ThrowGccString("Exception");
         }
      }
   }
}