DLL Programmer's Guide for TNS/R Systems

DLLs on a TNS/R System

DLL Programmer’s Guide for TNS/R Systems—522203-002

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Why Dynamically Linked Libraries?

For statically-linked programs, you must copy all shared libraries into your own

programs; thus, complete copies of these libraries appear in all the programs that use

them, and each copy consumes main memory and disk space. Also, whenever such a

library is changed, it must be relinked into all the programs that need those changes.

TNS/R shared runtime libraries (SRLs) offer some improvement, but DLLs are easier

to create and install than SRLs and so they are provided for you to use in building

applications.

Some key characteristics of DLLs are:

•

A single copy of a DLL in physical memory can be shared among multiple

processes.

•

A DLL that is shared among processes can appear at a different virtual address in

each process; and each instance has its own copy of global data that is available

to its process.

•

Multiple processes can use different versions of the same DLL simultaneously,

though each version must have a different name or be stored in a different location

in the file system.

Figure 1-2. An Application Made Up Of a Program And The DLLs It Needs

Program

DLL A DLL B DLL C

DLL D DLL E

DLL G

DLL F

VST012.vsd