[from the win32 sdk named pipe documentation]

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The simplest server process can use the CreateNamedPipe function to
create a single instance of a pipe, connect to a single client,
communicate with the client, disconnect the pipe, close the pipe
handle, and terminate. Typically, however, a server process must
communicate with multiple client processes. A server process can use a
single pipe instance by connecting to and disconnecting from each
client in sequence, but performance would be poor. To handle multiple
clients simultaneously, the server process must create multiple pipe
instances.

There are three basic strategies for servicing multiple pipe instances.

· Create multiple threads (and/or processes) with a separate thread
for each instance of the pipe. For an example of a multithreaded
server process, see Multithreaded Server.

· Overlap operations by specifying an OVERLAPPED structure in the
ReadFile, WriteFile, and ConnectNamedPipe functions. For an example of
a server process that uses overlapped operations, see Server Using
Overlapped Input and Output.

· Overlap operations by using the ReadFileEx and WriteFileEx
functions, which specify a completion routine to be executed when the
operation is complete. For an example of a server process that uses
completion routines, see Server Using Completion Routines.

 
The multithreaded server strategy is easy to write, because the thread
for each instance handles communications for only a single client. The
system allocates processor time to each thread as needed. But each
thread uses system resources, which is a potential disadvantage for a
server that handles a large number of clients. Other complications
occur if the actions of one client necessitate communications with
other clients (as for a network game program, where a move by one
player must be communicated to the other players).

With a single-threaded server, it is easier to coordinate operations
that affect multiple clients, and it is easier to protect shared
resources (for example, a database file) from simultaneous access by
multiple clients. The challenge of a single-threaded server is that it
requires coordination of overlapped operations in order to allocate
processor time for handling the simultaneous needs of the clients.

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