View source for TUT:Writing a Dynamically Loadable Object

== Initialization ==

After loading the shared object to memory, the <em>object loader</em> will look for an initialization function inside the shared object. The name of this function is <code>init_<em>name</em></code>, where "name" is the name of your extension. The name of the example module is "nstAgentPluginObject", so the loader will look for a function with the following prototype:

 void init_nstAgentPluginObject (void);

There's a complementary function, called <code>deinit_<em>name</em></code>, which is called when the module is unloaded, for example when the daemon is shutting down. Unsurprisingly, the prototype of the example deinit-function is:

 void deinit_nstAgentPluginObject (void);

These are the only two functions called by the object loaded. All other functions (and module-global variables) therefore should be declared <code>static</code>.

It is important to note that nothing prevents the agent from a second "load" of the same shared object. The module isn't actually loaded a second time, but the initialization function is run again. Modules should be able to handle that, for example by checking if they were already initialized when returning without further actions if so. The same applies to the de-initialization functions.

Further when the last unload happens the module is unloaded and so the code disappears. When this happens everything registered with the agent from the module must be unregistered since not doing so is an open invitation to core dumps.

You can check the names of currently loaded modules using the <code>UCD-DLMOD-MIB::dlmodName</code> OID.