Applications and Geodes: 1.6 Geodes: Writing Your Own Libraries

Creating a library geode is a simple step beyond creating a normal application. Libraries can have their own process threads or not; most libraries do not, though some will. To create a library geode, you have to do four things:

Declare the geode to be a library.
In the geode parameters ( .gp ) file, you must declare the type of the geode to be library.
Define an entry point routine.
Create a routine that initializes the library; this routine is called the "entry point routine" and is called each time the library is loaded.
Export the entry point routine.
Add another line in the geode parameters ( .gp ) file to export the library's entry point routine.
Set the geode's permanent name properly.
Most libraries have the extension of their permanent name be "lib." This helps identify it as a library when using Swat. The permanent name is defined in the geode parameters ( .gp ) file.

Defining a Library-the sound.gp File shows an example of the three changes you must make to the geode's parameters file to make it a library.

Code Display 7-1 Defining a Library--the sound.gp File

 # The Sound Library has the following three lines in its geode parameters file
# (sound.gp) different from how they might appear in an application.

#
# The permanent name of the geode might normally be sound.app if it is an
# application. A library typically has "lib" as its name extension.
#
name sound.lib

#
# Declare the type of the geode to be a library. Applications typically have a
# "process" aspect; many libraries do not. Libraries must also be declared to
# have a "library" aspect. (Note that the Sound Library is exceptional in that
# it has both a driver aspect and a library aspect.)
#
type driver, library, single

#
# Export the geode's entry point routine so the kernel may call it when the
# library is loaded. This routine must be defined somewhere in the geode's code.
# Note that it is exported with the "entry" line rather than the standard
# "export" line; this is to distinguish the exported routine as the entry
# point rather than a typical routine.
#
entry SoundEntry

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