When should we use volatile modifier in HMaster?

[yuhang li <89...@gmail.com>]

Hi all, I'm developing some new features based on HBase-1.2.9 and found  a
weird thing that， in class HMaster some properties are volatile, while
others are not volatile and I haven't found any  synchronization for them.
As far as I know, volatile is use to to guarantee visibility among multiple
threads. There is no doubt HMaster is accessed by many threads. So, why
there are only a small part of variables are volatile?

Re: When should we use volatile modifier in HMaster?

[yuhang li <89...@gmail.com>]

Thanks for your reply.
As you guessed, these non-volatile properties is initialized in a single
thread by invocation of method
"HMaster.finishActiveMasterInitialization(MonitoredTask
status)" and won't be changed anymore.
And now I get it, the way in which HMaster initialize itself. It use a
single thread to initialize its properties  that won't change, and then use
this single thread to start other threads that will access the unchanged
properties. According to "happens-before" rule, threads started by the
single thread would see any memory change made by the single thread before.
Am I right?


Stack <st...@duboce.net> 于2019年3月15日周五 下午12:39写道：

> On Thu, Mar 14, 2019 at 12:34 AM yuhang li <89...@gmail.com> wrote:
>
> > Hi all, I'm developing some new features based on HBase-1.2.9
>
>
> Its best to develop against master first and then we backport to other
> branches.
>
> You've seen announcements that hbase-1.2 is sunsetting.... that it'll be
> EOL'd in the not too distant future?
>
>
>
> > and found  a
> > weird thing that， in class HMaster some properties are volatile, while
> > others are not volatile and I haven't found any  synchronization for
> them.
> > As far as I know, volatile is use to to guarantee visibility among
> multiple
> > threads. There is no doubt HMaster is accessed by many threads. So, why
> > there are only a small part of variables are volatile?
> >
>
>
> Maybe paste an example of what you think a problematic use of volatile?
> That might be the best way to proceed. If non-volatile, then my guess is it
> is a property that is written on single-threaded startup and not changed
> ahead of the rest-of-all threads starting.
>
> Thanks,
> S
>

Re: When should we use volatile modifier in HMaster?

[Stack <st...@duboce.net>]

On Thu, Mar 14, 2019 at 12:34 AM yuhang li <89...@gmail.com> wrote:

> Hi all, I'm developing some new features based on HBase-1.2.9


Its best to develop against master first and then we backport to other
branches.

You've seen announcements that hbase-1.2 is sunsetting.... that it'll be
EOL'd in the not too distant future?



> and found  a
> weird thing that， in class HMaster some properties are volatile, while
> others are not volatile and I haven't found any  synchronization for them.
> As far as I know, volatile is use to to guarantee visibility among multiple
> threads. There is no doubt HMaster is accessed by many threads. So, why
> there are only a small part of variables are volatile?
>


Maybe paste an example of what you think a problematic use of volatile?
That might be the best way to proceed. If non-volatile, then my guess is it
is a property that is written on single-threaded startup and not changed
ahead of the rest-of-all threads starting.

Thanks,
S