Re: OSF/1/Digital UNIX/Tru64 UNIX spinlock code

Can I ask where this was left?

> Hi,
>
> I've managed to speak to someone knowledgeable at Digital in the UK
> who pointed me in the direction of a very interesting include file for
> Digital C/C++, namely /usr/include/alpha/builtins.h.
>
> It contains a series of function prototypes which are then converted
> into fast assembler sequences by the compiler. In particular a number
> of these seem highly suited for the task of rewriting the alpha
> spinlock code avoiding IPC semaphores.
>
> Amongst the many functions I believe the most relevant are, for the
> TAS() macro in s_lock.h:
>
> /*
> ** Interlocked "test for bit set and then set". Returns non-zero
> ** if bit was already set.
> */
> int __INTERLOCKED_TESTBITSS_QUAD(volatile void *__address, int __bit_position);
> int __INTERLOCKED_TESTBITSS_QUAD_RETRY(volatile void *__address,
> int __bit_position,
> int __retry,
> int *__status);
>
> Note that this call does _not_ generate a memory barrier. For the
> others, i.e. S_LOCK and S_UNLOCK perhaps the following might help:
>
> /*
> ** Acquire/release binary spinlock based on low-order bit of a longword.
> ** NOTE: Memory barrier generated after lock, before unlock.
> ** _RETRY variant returns non-zero on success within retry attempts.
> */
> void __LOCK_LONG(volatile void *__address);
> int __LOCK_LONG_RETRY(volatile void *__address, int __retry);
> void __UNLOCK_LONG(volatile void *__address);
>
> There are also counting semaphores if need be (all in the same file).
> If we change s_lock from msemaphore to long then the following patch
> compiles and is being tested by Adriaan Joubert as we speak. It
> probably crashes & burns but at least we can see if we get anywhere.
> My personal opinion is that it might be the way to go, I haven't
> looked carefully at S_LOCK etc. but will do so once Adriaan has
> crashed the copy of Postgres currently being compiled.
>
> ===File ~/src/hacks/s_lock.diff=====================
> --- s_lock.h.orig Wed Jun 14 15:33:28 2000
> +++ s_lock.h Wed Jun 14 16:11:29 2000
> @@ -252,10 +252,18 @@
> * Note that slock_t on the Alpha AXP is msemaphore instead of char
> * (see storage/ipc.h).
> */
> -#define TAS(lock) (msem_lock((lock), MSEM_IF_NOWAIT) < 0)
> -#define S_UNLOCK(lock) msem_unlock((lock), 0)
> -#define S_INIT_LOCK(lock) msem_init((lock), MSEM_UNLOCKED)
> -#define S_LOCK_FREE(lock) (!(lock)->msem_state)
> +#if 0
> +/* Original hack */
> +# define TAS(lock) (msem_lock((lock), MSEM_IF_NOWAIT) < 0)
> +# define S_UNLOCK(lock) msem_unlock((lock), 0)
> +# define S_INIT_LOCK(lock) msem_init((lock), MSEM_UNLOCKED)
> +# define S_LOCK_FREE(lock) (!(lock)->msem_state)
> +#else
> +/* Arrigo's hack */
> +# include <alpha/builtins.h>
> +# define TAS(lock) (__INTERLOCKED_TESTBITSS_QUAD(lock,0))
> +#endif
> +
>
> #else /* i.e. not __osf__ */
>
> ============================================================
>
> Ciao,
>
> Arrigo
>
> P.S. Yes, I don't really know what I am doing but trying my best to
> learn ;-)
>

--
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