[ovs-dev] [PATCH 1/5] ovs-thread: Add a comment

[YAMAMOTO Takashi]

> On Wed, Jan 15, 2014 at 12:41:20PM +0900, YAMAMOTO Takashi wrote:
>> Add a comment about implicit synchronization which
>> fat-rwlock seems to rely on.
>> 
>> Signed-off-by: YAMAMOTO Takashi <yamamoto at valinux.co.jp>
>> ---
>>  lib/ovs-thread.h | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>> 
>> diff --git a/lib/ovs-thread.h b/lib/ovs-thread.h
>> index 8cf2ecc..dab7510 100644
>> --- a/lib/ovs-thread.h
>> +++ b/lib/ovs-thread.h
>> @@ -447,6 +447,14 @@ void xpthread_join(pthread_t, void **);
>>   * Compared to pthread_key_t, ovsthread_key_t has the follow limitations:
>>   *
>>   *    - Destructors must not access thread-specific data (via ovsthread_key).
>> + *
>> + * Unlike pthread_key_t, this API implicitly serializes key removal
>> + * (ovsthread_key_delete) and thread exit. (destructor)
>> + * I.e.
>> + *    - ovsthread_key_delete ensures the completion of destructors for
>> + *      the key.
>> + *    - Once ovsthread_key_delete completed, no destructors for the key
>> + *      will be executed on thread exit.
>>   */
>>  typedef struct ovsthread_key *ovsthread_key_t;
> 
> I think I understand what you are saying, but I think that I would
> phrase it differently.  Does the following express what you mean?
> 
> diff --git a/lib/ovs-thread.c b/lib/ovs-thread.c
> index a20b2fd..18e524e 100644
> --- a/lib/ovs-thread.c
> +++ b/lib/ovs-thread.c
> @@ -592,7 +592,8 @@ ovsthread_key_create(ovsthread_key_t *keyp, void (*destructor)(void *))
>  }
>  
>  /* Frees 'key'.  The destructor supplied to ovsthread_key_create(), if any, is
> - * not called.
> + * not called.  This function returns only after any running destructors for
> + * 'key' complete execution.

'running destructors' is not exact.
i believe pthread api allows for concurrent exiting threads to
start executing the destructor after pthread_key_delete completed.
but this ovsthread one doesn't.  and fat-rwlock relies on it.

i think it's better to say the difference explicitly as
it guarantees more than pthread while using similar-looking names.
i was confused when reading fat-rwlock.

YAMAMOTO Takashi

>   *
>   * This function is similar to xpthread_key_delete(). */
>  void
> 
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