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Dynamic Data Exchange Message Flow
A typical DDE conversation consists of the following events:
- The client application initiates the conversation, and the server application
responds.
- The applications exchange data by any or all of the following methods:
- The server application sends data to the client at the client's request.
- The client application sends unsolicited data to the server application.
- The client application requests the server application to notify the client
whenever a data item changes (warm data link).
- The client application requests the server application to send data whenever
the data changes (hot data link).
- The server application carries out a command at the client's request.
- Either the client or server application terminates the conversation.
An application window that processes requests from a client or server must
process them strictly in the order they are received.
A client can establish conversations with more than one server; a server can
have conversations with more than one client. When handling messages from more
than one source, a client or server must process the messages of a given
conversation synchronously, but need not process all messages synchronously. In other
words, it can shift from one conversation to another as needed.
If an application is unable to process an incoming request because it is
waiting for a DDE response, it must prevent deadlock by posting a WM_DDE_ACK message with the fBusy member of the DDEACK structure set to 1. An application can also send a busy WM_DDE_ACK message
if, for any reason, it cannot process an incoming request within a reasonable
amount of time.
An application should be able to handle the failure of a client or server to
respond to a message within a certain time. Since the time-out interval may vary
depending on the nature of the application and the configuration of the user's
system (including whether it is connected to a network), the application
should provide a way for the user to specify the interval.
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