void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
assert(UseConcMarkSweepGC, "just checking");
MutexLockerEx x(CGC_lock,
Mutex::_no_safepoint_check_flag);
if (!is_cms_thread) {
assert(Thread::current()->is_VM_thread(), "Not a VM thread");
CMSSynchronousYieldRequest yr;
while (CMS_flag_is_set(CMS_cms_has_token)) {
// indicate that we want to get the token
set_CMS_flag(CMS_vm_wants_token);
CGC_lock->wait(true);
}
// claim the token and proceed
clear_CMS_flag(CMS_vm_wants_token);
set_CMS_flag(CMS_vm_has_token);
} else {
assert(Thread::current()->is_ConcurrentGC_thread(),
"Not a CMS thread");
// The following barrier assumes there's only one CMS thread.
// This will need to be modified is there are more CMS threads than one.
while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
set_CMS_flag(CMS_cms_wants_token);
CGC_lock->wait(true);
}
// claim the token
clear_CMS_flag(CMS_cms_wants_token);
set_CMS_flag(CMS_cms_has_token);
}
}
// Wait until the next synchronous GC or a timeout, whichever is earlier.
void ConcurrentMarkSweepThread::wait_on_cms_lock(long t) {
MutexLockerEx x(CGC_lock,
Mutex::_no_safepoint_check_flag);
set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
CGC_lock->wait(Mutex::_no_safepoint_check_flag, t);
clear_CMS_flag(CMS_cms_wants_token);
assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
"Should not be set");
}
// Wait until the next synchronous GC, a concurrent full gc request,
// or a timeout, whichever is earlier.
void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
MutexLockerEx x(CGC_lock,
Mutex::_no_safepoint_check_flag);
if (_should_terminate || _collector->_full_gc_requested) {
return;
}
set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
clear_CMS_flag(CMS_cms_wants_token);
assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
"Should not be set");
}
void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
assert(UseConcMarkSweepGC, "just checking");
MutexLockerEx x(CGC_lock,
Mutex::_no_safepoint_check_flag);
if (!is_cms_thread) {
assert(Thread::current()->is_VM_thread(), "Not a VM thread");
assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
clear_CMS_flag(CMS_vm_has_token);
if (CMS_flag_is_set(CMS_cms_wants_token)) {
// wake-up a waiting CMS thread
CGC_lock->notify();
}
assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
"Should have been cleared");
} else {
assert(Thread::current()->is_ConcurrentGC_thread(),
"Not a CMS thread");
assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
clear_CMS_flag(CMS_cms_has_token);
if (CMS_flag_is_set(CMS_vm_wants_token)) {
// wake-up a waiting VM thread
CGC_lock->notify();
}
assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
"Should have been cleared");
}
}
// Wait until the next synchronous GC, a concurrent full gc request,
// or a timeout, whichever is earlier.
void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) {
// Wait time in millis or 0 value representing infinite wait for a scavenge
assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive");
GenCollectedHeap* gch = GenCollectedHeap::heap();
double start_time_secs = os::elapsedTime();
double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS));
// Total collections count before waiting loop
unsigned int before_count;
{
MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
before_count = gch->total_collections();
}
unsigned int loop_count = 0;
while(!_should_terminate) {
double now_time = os::elapsedTime();
long wait_time_millis;
if(t_millis != 0) {
// New wait limit
wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS);
if(wait_time_millis <= 0) {
// Wait time is over
break;
}
} else {
// No wait limit, wait if necessary forever
wait_time_millis = 0;
}
// Wait until the next event or the remaining timeout
{
MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
if (_should_terminate || _collector->_full_gc_requested) {
return;
}
set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
assert(t_millis == 0 || wait_time_millis > 0, "Sanity");
CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis);
clear_CMS_flag(CMS_cms_wants_token);
assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
"Should not be set");
}
// Extra wait time check before entering the heap lock to get the collection count
if(t_millis != 0 && os::elapsedTime() >= end_time_secs) {
// Wait time is over
break;
}
// Total collections count after the event
unsigned int after_count;
{
MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
after_count = gch->total_collections();
}
if(before_count != after_count) {
// There was a collection - success
break;
}
// Too many loops warning
if(++loop_count == 0) {
warning("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1);
}
}
}
