Re: Simplelock v.s lock

[Adam Hoka <adam.hoka%gmail.com@localhost>]

On Thu, 17 Jun 2010 16:53:38 +0200
Putrycy <putrycydestengier%gmail.com@localhost> wrote:

> Hey guys. I am a noob in netbsd. I had some experience with linux before 
> though.
> During my work, ive approached a problem when i need to use a
> Linux-like spin locks.
> I found out that i need to use either lock or simplelock in NetBSD.
> My question is : what is the exact difference between those two ?
> According to the manual:
> 'struct simplelock
>               Provides a simple spinning mutex.  A processor will busy-wait
>               while trying to acquire a simplelock.  The simplelock operations
>               are implemented with machine-dependent locking primitives.
>               Simplelocks are usually used only by the high-level lock manager
>               and to protect short, critical sections of code.  Simplelocks
>               are the only locks that can be used inside an interrupt handler.
>               For a simplelock to be used in an interrupt handler, care must
>               be taken to disable the interrupt, acquire the lock, do any pro-
>               cessing, release the simplelock and re-enable the interrupt.
>               This procedure is necessary to avoid deadlock between the inter-
>               rupt handler and other threads executing on the same processor.
>      struct lock
>               Provides a high-level lock supporting sleeping/spinning until
>               the lock can be acquired.  The lock manager supplies both exclu-
>               sive-access and shared-access locks, with recursive exclusive-
>               access locks within a single thread.  It also allows upgrading a
>               shared-access lock to an exclusive-access lock, as well as down-
>               grading an exclusive-access lock to a shared-access lock.'
> Is the only difference that simplelocks are 'turining interrupts off'
> , and the other is not ??
> Thanks in advance for any reply.

Both of them are obsoleted in 5.0, use the newer mutex API, but for the record:

a spin lock enters a loop and keeps polling the lock, and thus wasting
resources if held too long. a sleeping lock gives up execution of the thread,
and puts it into the turnstile, to be signaled when the lock is relased

-- 
NetBSD - Simplicity is prerequisite for reliability