[haiku-gsoc] Re: XSI semaphore implamentation patch #2

On 2008-07-29 at 00:24:29 [+0200], Salvatore Benedetto <emitrax@xxxxxxxxx> 
wrote:
> 
> attached is a second patch of xsi semaphore implementation.
> It includes the SEM_UNDO features.
> 
> I actually spent more time than I though on this one, because
> the sem_undo list get accesed not only when a process exit,
> thus executing all its sem_undo request, but also when calling
> semctl with SETVAL or SETALL on a semaphore (all sem_undo request
> must be cleared, that is deleted).
> 
> I reworked it three times in order to keep it as simple as possible
> and eventually came up with a single global sem_undo list (sUndoList).
> I wanted to add as little as possible to the team structure.
> 
> The complexity of the algorithm when removing an element is of course O(n)

As are xsi_sem_undo() and IPC_RMID (or would be, if it removed the undo 
values).

> as I iterated through the list but only a simple short value has been
> to the team
> structure (at first it was a boolean value) and speed shouldn't really
> be a problem
> as I think we won't have many semaphores in the systems.

Er, and you didn't wonder whether trading performance for a few bytes per 
team that uses XSI semaphores might not be the best idea?

> Anyway, if it happens to be a problem, I'll try with another solution.

Well, I proposed one that doesn't have the performance issues. I wonder why 
you even asked.

> The code has been tested with bonnie++, which uses the SEM_UNDO feature, and
> it seems to works fine.
> 
> I've also fixed some bugs that weren't easy to discover by simple
> reviewing the code
> in the first patch and bonnie++ helped with this. In fact it now runs
> in multiprocesses mode.

Very nice. I hope the insight that code review won't uproot all bugs 
encourages you to actually write unit tests.

CU, Ingo

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