An IOU handle instance can be empty. Any attempt to use an empty handle as if it were a valid IOU object produces an RWTHRInvalidPointer exception. You can determine whether an IOU handle is empty by using the isValid() member of the handle instance.

The IOU mechanism is implemented using a handle-body architecture. The construction of an IOU handle does not result in the construction of a complete IOU object. To build a viable IOU object you must first construct an escrow object and bind that object to one or more IOU handles.

Use the static make() functions construct an IOU escrow object.

The RWTThreadEscrowImp template class in the Threading package has a static member function, make(), that dynamically allocates an escrow object and returns an RWTEscrowHandle instance bound to that escrow object. The RWTEscrowHandle instance can be assigned to, or used to initialize, an RWTIOUResult or RWTIOUEscrow handle instance, as in this example:

If you use the RWTRunnableIOUFunction and RWTThreadIOUFunction classes, found in the Threading package, you can avoid escrow construction entirely by letting these classes construct the escrow object for you. You can retrieve a handle to the internal escrow instance by calling the result() member function in these runnable classes. This function returns an RWTIOUResult handle instance.