On 11/09/2015 6:37 PM, Andrew Haley wrote:
On 09/11/2015 07:15 AM, David Holmes wrote:
On 11/09/2015 12:56 AM, Vitaly Davidovich wrote:
Sure, if you like, but that's a detail. We are arguing about what
colour to paint the bike shed. :)
The reason it may be more than just a bikeshed is because if this requires
more cleverness in the segfault handler, then it's yet more work to make
this happen. I agree it's an implementation detail, but I don't think it's
trivial (unless someone comes along and says that modifying the trap
handler to account for this type of scenario is trivial). One would also
need to modify the safepoint code in the VM to allow skipping all the
housekeeping it does typically, but I suspect this part is fairly easy.
Not sure how the safepoint code is supposed to know this particular
safepoint is "special".
I guess I don't know what the problem is: when you request a safepoint you
also pass a code saying what you want to happen.
There are actions that can also happen at a safepoint that are not part
of the VMOperation for which the safepoint was initiated:
// Various cleaning tasks that should be done periodically at safepoints
void SafepointSynchronize::do_cleanup_tasks() {
{
TraceTime t1("deflating idle monitors", TraceSafepointCleanupTime);
ObjectSynchronizer::deflate_idle_monitors();
}
{
TraceTime t2("updating inline caches", TraceSafepointCleanupTime);
InlineCacheBuffer::update_inline_caches();
}
{
TraceTime t3("compilation policy safepoint handler",
TraceSafepointCleanupTime);
CompilationPolicy::policy()->do_safepoint_work();
}
{
TraceTime t4("mark nmethods", TraceSafepointCleanupTime);
NMethodSweeper::mark_active_nmethods();
}
if (SymbolTable::needs_rehashing()) {
TraceTime t5("rehashing symbol table", TraceSafepointCleanupTime);
SymbolTable::rehash_table();
}
if (StringTable::needs_rehashing()) {
TraceTime t6("rehashing string table", TraceSafepointCleanupTime);
StringTable::rehash_table();
}
// rotate log files?
if (UseGCLogFileRotation) {
gclog_or_tty->rotate_log(false);
}
{
// CMS delays purging the CLDG until the beginning of the next
safepoint and to
// make sure concurrent sweep is done
TraceTime t7("purging class loader data graph",
TraceSafepointCleanupTime);
ClassLoaderDataGraph::purge_if_needed();
}
}
All the above happens at the end of SafepointSynchronize::begin, before
the VMOperation is processed.
David
-----
Andrew.
