Module handling rewrite

This page describes the planned unit handling rewrite. It is done in a branch in svn, the url of the branch is http://svn.freepascal.org/svn/fpc/branches/unitrw/compiler

While implementing this, it should be taken care of running this in multiple threads in the middle/far future.

Task list

• open file
• Parse header
• Parse uses
• Parse interface
• parse impl. header
• parse impl. uses

• load unit
  • find unit
  • load ppu header
  • load ppu interface
  • load ppu impl.

• write ppu
• write object file

Task queue

• each task gets a two lists: task which must be processed before itself and tasks which depend on itself
• each task class gets a counter each time a new task to process is search, that counter is increased when searching a task to process,
• the queue is walked if a task without empty dependencies is found, it is moved to the end of the queue
• if a task is found with the same number as the current queue walking, the dependencies can't be resolved => error
• if a task with an empty dependencies list is found, it is executed after it is finished, it gets removed from the dependency lists of tasks waiting for it

Misc

Two lesser problems with the module system:

• Currently there is no way to have a set of units in one (or two) files. It would clean up tremendously if the all .ppu's and all .o/.a's could be in one file (or one file each), and the need for a dir structure to store all units would go away.
• Currently there is no scheme to efficiently have a different set of units in the path. E.g. .ppu's suitable for dynamic linking, units that are a result of devirtualization attempts etc, short of have separate hierarchies. I personally didn't like the oder attempts (shared/ and smart/ directory) with separate hierarchies.