Let Tools Be Started as Needed

To design your protocol to be completely open, you want the system to start tools only as needed. When you let a new tool instance be started only as needed, you provide the user with more flexibility and more efficient use of resources such as CPU, screen real estate, and swap space. The ToolTalk service has several features that assume the responsibility of determining when to start a new tool instance:

• The ToolTalk service allows messages and type signatures to have “start” reliability. Start reliability means that if no eligible recipient of a message is running (or willing to accept the request), the ToolTalk service will start an instance of the type of tool which is statically registered to handle or observe that message.

• The ToolTalk service allows each process type (ptype) to specify the maximum number of its instances that may be started in a given session.

• The ToolTalk service offers each request to all eligible running handlers before it starts a new tool instance. An eligible handler can accept or reject a request based on its own criteria (such as its ability to take on a new task; whether or not it has unsaved changes; idle time; iconic state; or whether or not the user has indicated that the tool is free to accept new work).