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Javier Guerra Giraldez wrote:
On Tuesday 24 June 2008, Jérôme Vuarand wrote:
That is quite an interesting thread, though I'd like to come back to a
point that has been discarded too quickly in my opinion.

2008/6/19 Javier Guerra <>:
An obvious improvement might be to use finer locks, maybe one per
mutable object; but a pthread mutex lock weights between 40 and 64
bytes each.  way too much.  readers/writer locks are even bigger.

this days i've been reading about lock implementations, and found this (, reimplemented in C i get 4 byte locks, and first tests show that could also work at 1byte. they're also noticeably faster than pthread locks, especially in the non-contented case (up to 60-70% faster).

the non-contented case is interesting, because since they're totally userspace in this case (only call the kernel if the lock is contented), and using a lock per object means a lot less contentions and higher opportunity for concurrency.

Interesting. It works like critical sections on Windows, but taking 6 times less space (a CS in Windows takes 24 bytes).

Thanks for the link.