This interface provides access to the runtime machinery that raises exceptions.

UNSAFE INTERFACE RTException;

IMPORT RT0;

PROCEDURE Raise (VAR a: RT0.RaiseActivation) RAISES ANY;

raise the exception described by a

PROCEDURE ResumeRaise (VAR a: RT0.RaiseActivation) RAISES ANY;

after a TRY-FINALLY handler has been executed, restart the processing of the execption. It is assumed that there is a handler for this exception

PROCEDURE SetBackstop (h: Backstop): Backstop;

Sets the current backstop to h and returns the previous handler.

PROCEDURE InvokeBackstop (VAR a: RT0.RaiseActivation;
                          raises: BOOLEAN) RAISES ANY;

Invokes the current backstop.

TYPE Backstop = PROCEDURE (VAR a: RT0.RaiseActivation;
                           raises: BOOLEAN) RAISES ANY;

PROCEDURE DumpStack ();

If possible, produce a diagnostic stack dump on stderr

END RTException.

Safety: The arg and aux_info fields of a RaiseActivation are gigantic loopholes. They may contain traced references or any other data. As long as the activation stays on the stack, the collector will handle the traced references properly. Code that copies the activation data off the stack is <<EM>>very<<EM>> dangerous.

Unhandled Exceptions:

When an exception is raised but not handled, the current backstop handler is invoked, h(a,r). The current activation information is in a and the flag r indicating whether the failure was due to a restrictive RAISES clause.

There is only one backstop handler per process.

The default backstop handler (represented by NIL) converts the failing exception to

           RuntimeError.E(RuntimeError.T.UnhandledException)  "or"
           RuntimeError.E(RuntimeError.T.BlockedException)

The default backstop preserves the module, line number, and pc information in the activation. It sets aux_info[0] to the exception that was not handled and sets aux_info[1] to the argument passed to that exception.

• m3core/src/runtime/common/RTException.m3
• m3core/src/runtime/ex_frame/RTExFrame.m3