When a commodity opens its broker, it can ask Commodities Exchange not to launch another broker with the same name (nb_Name). This uniqueness feature's purpose is to prevent the user from starting duplicate commodities. If a commodity asks, Commodities Exchange will not only refuse to create a new, similarly named broker, but it will also notify the original commodity if someone tries to do so. A commodity tells Commodities Exchange not to allow duplicates by setting certain bits in the nb_Unique field of the NewBroker structure it sends to CxBroker(): NBU_UNIQUE bit 0 NBU_NOTIFY bit 1 Setting the NBU_UNIQUE bit prevents duplicate commodities. Setting the NBU_NOTIFY bit tells Commodities Exchange to notify a commodity if an attempt was made to launch a duplicate. Such a commodity will receive a CXM_COMMAND CxMessage with an ID of CXCM D_UNIQUE when someone tries to duplicate it. Because the uniqueness feature uses the name a programmer gives a commodity to differentiate it from other commodities, it is possible for completely different commodities to share the same name, preventing th e two from coexisting. For this reason, a commodity should not use a name that is likely to be in use by other commodities (like "filter" or "hotkey"). When HotKey gets a CXCMD_UNIQUE CxMessage, it shuts itself down. HotKey and all the windowless commodities that come with the 2.0 Workbench shut themselves down when they get a CXCMD_UNIQUE CxMessage. Because the user will expect all windowless commodit ies to work this way, all windowless commodities should follow this standard. When the user tries to launch a duplicate of a system commodity that has a window, the system commodity moves its window to the front of the display, as if the user had clicked the "Show" gadget in the controller program's window. A windowed commodity should mimic conventions set by existing windowed system commodities, and move its window to the front of the display.
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