1. All threads use library at same (virtual) address

   If that address is already used by the thread, the library code, must be relocated in that thread's address space.

2. PIC - library code written as position independent code.

   Each process maintains a table of addresses of shared routines as mapped into the process.

   Position independent call: address of the call is at an offset in the table. The call is indirect through the table.

Windows: dynamic link libraries - .dll

Linux: shared objects - .so

But, versioning problem ...