20.4. Using Runtime Shared Libraries

Runtime shared libraries are a way to share assets and libraries among multiple .swf files on the same domain. This is useful when you have several .swf files that comprise an application or that span several applications deployed in the same domain in which each .swf file utilizes many common assets and/or libraries. For example, if a.swf and b.swf both utilize the same subset of 25 classes and embedded images that add up to 100 KB, the user has to download the same 100 KB twice, once for each .swf.

The theory behind runtime shared libraries involves a concept called linking. All .swf files employ one or both forms of linking: static and dynamic. By default, all linking is static. When an asset or source file is statically linked with an .swf, it is compiled into the .swf. Dynamic linking means that the asset or source file is not compiled into the .swf, but the .swf has a reference to an .swf into which it has been compiled. Through dynamic linking, you can specify certain elements that should not be compiled into an .swf to reduce the total file size of the .swf. The .swf is then linked to another .swf where the elements have been compiled. This allows you to extract common elements from two or more .swf files and place them into another .swf to which all the .swf files are linked dynamically. This new .swf is called a runtime shared library.