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[Bulat Bulat via freebsd-questions]

Thanks, Matthew and Patrick.

I am currently reading about locking in kernel, mostly man pages and headers
related to topic. That is various kinds of mutexes, rwlocks, shared locks, and the like.
Also I read boot - design and implementation of freebsd.

Then I started reading .c files and stuck on kern/subr_turnstile.
What the structure is and the purpose of it for me is understandable, how it is being
added when thread blocks and how it is being removed after wakeup().

However, the meaning of ts_free member in turnstile structure for me is unclear.
My understanding: when thread discovers than lock's turnstile is already present
at turnstile chain it adds its own turnstile to lock's turnstile's ts_free
and after it wokes up it regrabs turnstile from the same
ts_free list of lock's turnstile. But why does it so, if it already has its own turnstile, what the
meaning of putting of turnstile to free list only for regrabbing it later.

Thanks.
bnm

[Matthew Seaman]

Post by Bulat Bulat via freebsd-questions
However, the meaning of ts_free member in turnstile structure for me is unclear.
My understanding: when thread discovers than lock's turnstile is already present
at turnstile chain it adds its own turnstile to lock's turnstile's ts_free
and after it wokes up it regrabs turnstile from the same
ts_free list of lock's turnstile. But why does it so, if it already has its own turnstile, what the
meaning of putting of turnstile to free list only for regrabbing it later.

This is definitely a question for freebsd-***@...

Cheers,

Matthew

[Mehmet Erol Sanliturk]

Post by Bulat Bulat via freebsd-questions

Post by Bulat Bulat via freebsd-questions
However, the meaning of ts_free member in turnstile structure for me is

unclear.

Post by Bulat Bulat via freebsd-questions
My understanding: when thread discovers than lock's turnstile is already

present

Post by Bulat Bulat via freebsd-questions
at turnstile chain it adds its own turnstile to lock's turnstile's

ts_free

Post by Bulat Bulat via freebsd-questions
and after it wokes up it regrabs turnstile from the same
ts_free list of lock's turnstile. But why does it so, if it already has

its own turnstile, what the

Post by Bulat Bulat via freebsd-questions
meaning of putting of turnstile to free list only for regrabbing it

later.
Cheers,
Matthew

This is

put to free list - take it from free list .


A possible another method is to use

dispose - allocate

pair .


When dispose - allocate was taking long time ( in old times ) , the "put to
free - take from free" method was in use .


I am not saying that the reason of the use in your case is that , but there
was such a method in older times .


Mehmet Erol Sanliturk