RFR 8027434: "-XX:OnOutOfMemoryError" uses fork instead of vfork

[Thomas Stüfe]

Hi,

I think there is no reason at all to not always to use vfork() here
(in the linux implementation for fork_and_exec()).

The concerns with vfork() I outlined in
http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-September/055333.html
do not apply here. This is a very simple case, no stdio redirection,
no environment change, nothing. So, I would just exchange fork() for
vfork().

Best Regards, Thomas

On Thu, Sep 27, 2018 at 3:22 PM, David Holmes <david.holmes at oracle.com> wrote:
> Hi,
>
> On 27/09/2018 8:18 AM, Muthusamy Chinnathambi wrote:
>>
>> Hi David,
>>
>>> That doesn't work.
>>
>> I get your point. My bad.
>>
>>> Only the caller knows why it is being called.
>>
>> Please find the updated webrev at
>> http://cr.openjdk.java.net/~mchinnathamb/8027434/webrev.02/
>> This now uses a static helper to decide.
>
>
> Sorry but I really don't like this version using is_forkmode_vfork. It's
> awkward to introduce a Linux specific feature into a shared API. But I think
> the best way to do this would be to introduce a new default parameter to
> os::fork_and_exec
>
> static int fork_and_exec(char *cmd, bool use_vfork_if_available = false);
>
> then the impl in o_linux.cpp which use the arg to select fork or vfork. And
> vmError will do:
>
> if (os::fork_and_exec(cmd, true) < 0) {
>
> Thanks,
> David
>
>
>> Regards,
>> Muthusamy C
>>
>> -----Original Message-----
>> From: David Holmes
>> Sent: Friday, September 21, 2018 7:27 PM
>> To: Muthusamy Chinnathambi <muthusamy.chinnathambi at oracle.com>;
>> hotspot-runtime-dev at openjdk.java.net
>> Subject: Re: RFR 8027434: "-XX:OnOutOfMemoryError" uses fork instead of
>> vfork
>>
>> Sorry for the delay.
>>
>> On 19/09/2018 7:48 AM, Muthusamy Chinnathambi wrote:
>>>
>>> Hi David,
>>>
>>> Please find the updated webrev at
>>> http://cr.openjdk.java.net/~mchinnathamb/8027434/webrev.01/
>>> Instead of creating a static helper, I have moved the decision to the
>>> fork_and_exec routine itself.
>>
>>
>> That doesn't work. Just because we have an OnOutOfMemoryError handler
>> set it doesn't mean the call to os::fork_and_exec was made to run that
>> handler. Only the caller knows why it is being called.
>>
>> David
>>
>>> Tested with mach5 hs-tier1-4.
>>>
>>> Regards,
>>> Muthusamy C
>>>
>>> -----Original Message-----
>>> From: Muthusamy Chinnathambi
>>> Sent: Friday, September 14, 2018 12:03 PM
>>> To: David Holmes <david.holmes at oracle.com>;
>>> hotspot-runtime-dev at openjdk.java.net
>>> Subject: RE: RFR 8027434: "-XX:OnOutOfMemoryError" uses fork instead of
>>> vfork
>>>
>>> Hi David,
>>>
>>>> please refactor into a static helper function
>>>
>>> Sure, I will change and get back after testing.
>>>
>>> Regards,
>>> Muthusamy C
>>>
>>> -----Original Message-----
>>> From: David Holmes
>>> Sent: Friday, September 14, 2018 11:16 AM
>>> To: Muthusamy Chinnathambi <muthusamy.chinnathambi at oracle.com>;
>>> hotspot-runtime-dev at openjdk.java.net
>>> Subject: Re: RFR 8027434: "-XX:OnOutOfMemoryError" uses fork instead of
>>> vfork
>>>
>>> Hi Muthusamy,
>>>
>>> Instead of duplicating all the code - which I think only differs in the
>>> fork versus vfork line - please refactor into a static helper function
>>> that takes a boolean vfork and call that from
>>> fork_and_exec/vfork_and_exec selecting fork or vfork as appropriate.
>>>
>>> I'm still mulling over whether there is a cleaner way to do this other
>>> than introducing a linux only entry to the os class.
>>>
>>> Thanks,
>>> David
>>>
>>>
>>> On 14/09/2018 1:55 PM, Muthusamy Chinnathambi wrote:
>>>>
>>>> Hi all,
>>>>
>>>> Could you review this fix for JDK-8027434 - to use vfork instead of fork
>>>> for -XX:OnOutOfMemoryError.
>>>>
>>>> See bug comments for more details.
>>>>
>>>> Bug URL: https://bugs.openjdk.java.net/browse/JDK-8027434
>>>> Webrev URL: http://cr.openjdk.java.net/~mchinnathamb/8027434/webrev.00/
>>>>
>>>> Tested with mach5 hs-tier1-4.
>>>>
>>>> Regards,
>>>> Muthusamy C
>>>>
>