[Freeswitch-dev] upgrade a rdlock to wrlock

[Christopher Rienzo]

Even if that works, what happens when two threads that have a read lock
attempt to switch to a write lock simultaneously?  How does the thread know
it got the write lock first and the data is unchanged?



On Thu, Aug 18, 2011 at 12:20 PM, Anthony Minessale <
anthony.minessale at gmail.com> wrote:

> can't you just write lock it right away?
>
> On Thu, Aug 18, 2011 at 7:19 AM, Christopher Rienzo <cmrienzo at gmail.com>
> wrote:
> > I forgot to mention that you'd have to repeat the find operation once you
> > get the write lock since there is a small window between the unlock and
> lock
> > where another thread may have created the item.
> >
> >
> > On Thu, Aug 18, 2011 at 6:42 AM, Christopher Rienzo <cmrienzo at gmail.com>
> > wrote:
> >>
> >> Unlock the read lock and then lock as a write lock.
> >>
> >> On Aug 17, 2011 8:20 PM, "Seven Du" <dujinfang at gmail.com> wrote:
> >>
> >> Hi,
> >>
> >>
> >> Just wondering how to upgrade a read lock to a write lock, say I do a
> >> find_or_create_item_in_queue()
> >> switch_thread_rwlock_rdlock(lock);
> >> find an item from queue, if not found, create one
> >> switch_thread_rwlock_upgrade_to_wrlock(lock);
> >> write
> >> switch_thread_rwlock_unlock(lock);
> >> Thanks
> >> --
> >> Seven Du
> >> About: http://about.me/dujinfang
> >> Blog: http://www.dujinfang.com
> >> Proj:  http://www.freeswitch.org.cn
> >> Sent with Sparrow
> >>
> >>
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> >
> >
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>
>
>
> --
> Anthony Minessale II
>
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