4.5.1 Tradeoffs for Dynamic Libraries

Dynamic libraries introduce some additional tradeoff considerations:

• Smaller a.out file

  Deferring binding of the library routines until execution time means that the size of the executable file is less than the equivalent executable calling a static version of the library; the executable file does not contain the binaries for the library routines.

• Possibly smaller process memory utilization

  When several processes using the library are active simultaneously, only one copy of the library resides in memory and is shared by all processes.

• Possibly increased overhead

  Additional processor time is needed to load and link-edit the library routines during runtime. Also, the library’s position-independent coding might execute more slowly than the relocatable coding in a static library.

• Possible overall system performance improvement

  Reduced memory utilization due to library sharing should result in better overall system performance (reduced I/O access time from memory swapping).

Performance profiles among programs vary greatly from one to another. It is not always possible to determine or estimate in advance the performance improvement (or degradation) between dynamic versus static libraries. However, if both forms of a needed library are available to you, it would be worthwhile to evaluate the performance of your program with each.