A DLL is initialized and terminated by the default _DLL_InitTerm function. When a process gains access to the DLL, this function initializes the necessary environment for the DLL, including storage, semaphores, and variables. When the process frees its access to the DLL, the _DLL_InitTerm function terminates the DLL environment created for that process. The _DLL_InitTerm function is called automatically when you link to the DLL.

The _DLL_InitTerm function can be executed once when the DLL is first loaded into memory, or it can be executed each time a new process first accesses the DLL. The LIBRARY statement in the module-definition file is used to specify when the _DLL_InitTerm function is to be executed. Following is a list of of the available options for the LIBRARY statement.

Options

Result
INITINSTANCE
The _DLL_InitTerm function is called the first time the DLL is loaded for each process that accesses the DLL.
INITGLOBAL
The _DLL_InitTerm function is called only the very first time the DLL is loaded. This is the default.
TERMINSTANCE
The _DLL_InitTerm function is called the last time the DLL is freed for each process that accesses the DLL.
As an example, the following statement, identifies the executable file as a DLL and specifies that SAMPLE03 is the name of the DLL:

LIBRARY SAMPLE03 INITINSTANCE TERMINSTANCE

It also specifies that the _DLL_InitTerm function is to be called the first time the DLL is loaded for each process that calls the DLL and the last time the DLL is freed for each process that calls the DLL.

When OS/2 starts executing a DLL, it sets the CPU registers to known values, but only for 16-bit DLLs. All 32-bit DLLs are called with a stack frame, like all other API calls.

Initialization/termination functions can be written in a high-level language. For more information on writing your own initialization/termination function, see Creating an Initialization/Termination Function.

---

[Back] [Next]