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");
}
}
}
}