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Re: volatile/atomic issues in the new BDB cache

From: Philip Martin <philip_at_codematters.co.uk>
Date: 2006-01-28 13:44:24 CET

Branko ╚ibej <brane@xbc.nu> writes:

> Philip Martin wrote:
>> First issue: the new "spinlock" appears to use CAS more than
>> necessary, I think it can be simplified to this:
> Don't we all wish. Saith apr_atomic.h:
>> * @warning do not mix apr_atomic's with the CAS function.
>> * on some platforms they may be implemented by different mechanisms

I think we should add a similar warning to the svn__atomic macros.

>> Second issue: bdb_cache_state is declared as "volatile svn__atomic_t"
>> and always accessed through the svn__atomic_xxx functions, and that
>> combination is obviously intended to provide "thread safety". I guess
>> it's reasonable in practice :) However, the svn__atomic_xxx functions
>> are also used to access the the panic flag in bdb_env_t and yet that
>> flag is declared as plain svn_boolean_t, that's confusing.
> Really? Saith bdb_env_t in env.c:
>> svn__atomic_t panic;

Yes, I made a mistake there.

> It's not svn_boolean_t, but I agree it should be volatile.


> The return
> value of svn_fs_bdb__get_panic is boolean, but that's irrelevant.

Perhaps that's why I made my mistake; I agree it's OK.

Philip Martin
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Received on Sat Jan 28 13:45:08 2006

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