RFR: 8011882: Replace spin loops as back off when suspending

[Rickard Bäckman]

On Apr 12, 2013, at 7:34 AM, David Holmes wrote:

> On 12/04/2013 3:01 PM, Rickard Bäckman wrote:
>> 
>> On Apr 12, 2013, at 1:04 AM, David Holmes wrote:
>> 
>>> On 11/04/2013 11:02 PM, Rickard Bäckman wrote:
>>>> On Apr 11, 2013, at 2:39 PM, David Holmes wrote:
>>>>> So what did you mean about pthread_semaphore (what is that anyway?) ??
>>>> 
>>>> Never mind, pthread condition variables.
>>> 
>>> Ah I see.
>>> 
>>>>> 
>>>>> I really, really, really don't like seeing three versions of this class :( Can't BSD and Linux at least share a POSIX version? (And I wonder if we can actually mix-n-match UI threads on Solaris with POSIX semaphores on Solaris?)
>>>> 
>>>> I don't like it either, our OS code isn't really helpful when it comes do reusing things :) Not sure how I would layout things to make them only available on BSD (Not Mac) and Linux. I guess os_posix.hpp with lots of #ifdefs, but I'm not sure I"m feeling that happy about that.
>>> 
>>> Why would the os_posix version need a lot of ifdefs?
>> 
>> Well, I guess we would need:
>> 
>> (in ifdef pseudo language)
>> 
>> #ifdef (LINUX || (BSD && !APPLE))
>> …
>> #endif
> 
> But if it isn't "posix" then we won't be building os_posix - right?

Linux, Solaris, Bsd & Mac builds and include os_posix. They are all "implementing posix" we are just not using the same semaphore implementation on all of them.

> 
>> The second interesting problem this will get us into is that sem_t is not declared in this context. Where do we put the #include <semaphore.h>? Impossible in os_posix.hpp since it is included in the middle of a class definition. I could put it in os.hpp in the #ifdef path that does the jvm_platform.h includes, not sure if that is very pretty either.
> 
> Semaphores are already used by the signal handler thread - semaphore.h is included in os_linux.cpp etc, so why would os_posix be any different ?
> 
> But couldn't we just have a Semaphore.h/cpp with any needed ifdefs?
> 
>>> Do we really have four versions:
>>> - linux (posix)
>>> - BSD (posix)
>>> - Solaris
>>> - Mac (different to BSD?)
>>> 
>> 
>> 3:
>> 1) linux & bsd uses the sem_ interface
>> 2) solaris uses the sema_ interface
>> 3) mac uses the semaphore_ interface
> 
> Okay but if mac is BSD why can't we use bsd ie posix interface instead of the mach semaphore_ ?

Because apple decided not to implement sem_timedwait.
On Solaris we use sema_ because sem_ requires us to link with -lrt which we currently don't (and I'm not really feeling like adding it)

> 
> 
> BTW I like the idea of using the semaphore, we're just haggling on the details. ;-)

I'm fine with that :)

/R

> 
> Thanks,
> David
> 
>> /R
>> 
>>> ??
>>> 
>>> David
>>> -----
>>