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8234086: VM operation can be simplified

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Reviewed-by: kbarrett, dholmes, dcubed
This commit is contained in:
Robbin Ehn 2019-11-29 12:09:25 +01:00
parent 6230791e9e
commit 3d7d54b145
14 changed files with 75 additions and 159 deletions
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29
src/hotspot/share/runtime/synchronizer.cpp
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@ -529,8 +529,7 @@ struct SharedGlobals {
};
static SharedGlobals GVars;
static int MonitorScavengeThreshold = 1000000;
static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
static int _forceMonitorScavenge = 0; // Scavenge required and pending
static markWord read_stable_mark(oop obj) {
markWord mark = obj->mark();
@ -915,7 +914,17 @@ static bool monitors_used_above_threshold() {
bool ObjectSynchronizer::is_cleanup_needed() {
if (MonitorUsedDeflationThreshold > 0) {
return monitors_used_above_threshold();
if (monitors_used_above_threshold()) {
return true;
}
}
return needs_monitor_scavenge();
}
bool ObjectSynchronizer::needs_monitor_scavenge() {
if (Atomic::load(&_forceMonitorScavenge) == 1) {
log_info(monitorinflation)("Monitor scavenge needed, triggering safepoint cleanup.");
return true;
}
return false;
}
@ -983,8 +992,6 @@ void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
// we'll incur more safepoints, which are harmful to performance.
// See also: GuaranteedSafepointInterval
//
// The current implementation uses asynchronous VM operations.
//
// If MonitorBound is set, the boundry applies to
// (g_om_population - g_om_free_count)
// i.e., if there are not enough ObjectMonitors on the global free list,
@ -994,16 +1001,12 @@ void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
static void InduceScavenge(Thread* self, const char * Whence) {
// Induce STW safepoint to trim monitors
// Ultimately, this results in a call to deflate_idle_monitors() in the near future.
// More precisely, trigger an asynchronous STW safepoint as the number
// More precisely, trigger a cleanup safepoint as the number
// of active monitors passes the specified threshold.
// TODO: assert thread state is reasonable
if (ForceMonitorScavenge == 0 && Atomic::xchg(&ForceMonitorScavenge, 1) == 0) {
// Induce a 'null' safepoint to scavenge monitors
// Must VM_Operation instance be heap allocated as the op will be enqueue and posted
// to the VMthread and have a lifespan longer than that of this activation record.
// The VMThread will delete the op when completed.
VMThread::execute(new VM_ScavengeMonitors());
if (Atomic::xchg (&_forceMonitorScavenge, 1) == 0) {
VMThread::check_for_forced_cleanup();
}
}
@ -1681,7 +1684,7 @@ void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* co
Thread::muxRelease(&gListLock);
}
ForceMonitorScavenge = 0; // Reset
Atomic::store(&_forceMonitorScavenge, 0); // Reset
OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));