When you create a DLL, you can use the DATA statement in the module-definition file to define the default attributes for data segments within the DLL. The default condition is for the DLL to have a unique copy of the automatic data segment for each process. You can specify DATA MULTIPLE READWRITE in the module-definition file to cause OS/2 to create a separate copy of all the DLL data for each process that uses the DLL (instance data). Modifications made by one process do not affect other processes.

You also can specify different attributes for different sets of data by using the #pragma data_seg and #pragma alloc_text directives to define your own data and code segments. You can list the segments in the module-definition file under the heading SEGMENTS and specify attributes for each.

    SEGMENTS
       mydata SINGLE READONLY
       mycode PRELOAD

Any segments that you do not specify under SEGMENTS are given the attributes specified by the DATA or CODE statement, depending on the type of segment.