[9] RFR(S): 8153527: break_tty_lock_for_safepoint causes "assert(false) failed: bad tag in log" and broken compile log

[Nils Eliasson]

Resizeable is better, but then we assert on expanding the stringbuffer 
while being under a different ResourceMark.

Regards,
Nils

On 2016-04-15 19:44, Vladimir Kozlov wrote:
> Use resizable stream:
>
> stringStream(size_t initial_bufsize = 256);
>
> 1024 may not be enough.
>
> Thanks,
> Vladimir
>
> On 4/15/16 8:10 AM, Nils Eliasson wrote:
>> Hi,
>>
>> Please review this fix of print opto_assembly.
>>
>> Summary:
>> The compilelog can get corrupted and the VM may assert on "failed: 
>> bad tag in log".
>>
>> When printing assembly in output.cpp we first take the ttylock, print 
>> the head and then the method metadata. However the
>> metadata printing makes a vm entry and may block for a safepoint and 
>> will then release the lock
>> (break_tty_lock_for_safepoint). After that some of the other compiler 
>> thread that haven't safepointed will take the lock
>> and the broken log will be a fact when the safepoint is over and the 
>> first thread starts logging again.
>>
>> Solution:
>> Print the method metadata to a temporary buffer, then take the tty lock.
>>
>> Testing:
>> Repro from bug stops failing.
>> Running :hotspot_all 
>> (http://jdash.se.oracle.com/rbt/rbt-nils.eliasson-compiler_control-20160415-1508-10854)
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8153527
>> Webrev: http://cr.openjdk.java.net/~neliasso/8153527/webrev.01/
>>
>> Regards,
>> Nils Eliasson