--- a/hotspot/src/share/vm/runtime/park.cpp Thu Jan 23 16:02:14 2014 -0500
+++ b/hotspot/src/share/vm/runtime/park.cpp Fri Jan 24 09:28:47 2014 +0100
@@ -59,58 +59,22 @@
// Start by trying to recycle an existing but unassociated
// ParkEvent from the global free list.
- for (;;) {
- ev = FreeList ;
- if (ev == NULL) break ;
- // 1: Detach - sequester or privatize the list
- // Tantamount to ev = Swap (&FreeList, NULL)
- if (Atomic::cmpxchg_ptr (NULL, &FreeList, ev) != ev) {
- continue ;
+ // Using a spin lock since we are part of the mutex impl.
+ // 8028280: using concurrent free list without memory management can leak
+ // pretty badly it turns out.
+ Thread::SpinAcquire(&ListLock, "ParkEventFreeListAllocate");
+ {
+ ev = FreeList;
+ if (ev != NULL) {
+ FreeList = ev->FreeNext;
}
-
- // We've detached the list. The list in-hand is now
- // local to this thread. This thread can operate on the
- // list without risk of interference from other threads.
- // 2: Extract -- pop the 1st element from the list.
- ParkEvent * List = ev->FreeNext ;
- if (List == NULL) break ;
- for (;;) {
- // 3: Try to reattach the residual list
- guarantee (List != NULL, "invariant") ;
- ParkEvent * Arv = (ParkEvent *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
- if (Arv == NULL) break ;
-
- // New nodes arrived. Try to detach the recent arrivals.
- if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
- continue ;
- }
- guarantee (Arv != NULL, "invariant") ;
- // 4: Merge Arv into List
- ParkEvent * Tail = List ;
- while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
- Tail->FreeNext = Arv ;
- }
- break ;
}
+ Thread::SpinRelease(&ListLock);
if (ev != NULL) {
guarantee (ev->AssociatedWith == NULL, "invariant") ;
} else {
// Do this the hard way -- materialize a new ParkEvent.
- // In rare cases an allocating thread might detach a long list --
- // installing null into FreeList -- and then stall or be obstructed.
- // A 2nd thread calling Allocate() would see FreeList == null.
- // The list held privately by the 1st thread is unavailable to the 2nd thread.
- // In that case the 2nd thread would have to materialize a new ParkEvent,
- // even though free ParkEvents existed in the system. In this case we end up
- // with more ParkEvents in circulation than we need, but the race is
- // rare and the outcome is benign. Ideally, the # of extant ParkEvents
- // is equal to the maximum # of threads that existed at any one time.
- // Because of the race mentioned above, segments of the freelist
- // can be transiently inaccessible. At worst we may end up with the
- // # of ParkEvents in circulation slightly above the ideal.
- // Note that if we didn't have the TSM/immortal constraint, then
- // when reattaching, above, we could trim the list.
ev = new ParkEvent () ;
guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ;
}
@@ -124,13 +88,14 @@
if (ev == NULL) return ;
guarantee (ev->FreeNext == NULL , "invariant") ;
ev->AssociatedWith = NULL ;
- for (;;) {
- // Push ev onto FreeList
- // The mechanism is "half" lock-free.
- ParkEvent * List = FreeList ;
- ev->FreeNext = List ;
- if (Atomic::cmpxchg_ptr (ev, &FreeList, List) == List) break ;
+ // Note that if we didn't have the TSM/immortal constraint, then
+ // when reattaching we could trim the list.
+ Thread::SpinAcquire(&ListLock, "ParkEventFreeListRelease");
+ {
+ ev->FreeNext = FreeList;
+ FreeList = ev;
}
+ Thread::SpinRelease(&ListLock);
}
// Override operator new and delete so we can ensure that the
@@ -164,56 +129,21 @@
// Start by trying to recycle an existing but unassociated
// Parker from the global free list.
- for (;;) {
- p = FreeList ;
- if (p == NULL) break ;
- // 1: Detach
- // Tantamount to p = Swap (&FreeList, NULL)
- if (Atomic::cmpxchg_ptr (NULL, &FreeList, p) != p) {
- continue ;
+ // 8028280: using concurrent free list without memory management can leak
+ // pretty badly it turns out.
+ Thread::SpinAcquire(&ListLock, "ParkerFreeListAllocate");
+ {
+ p = FreeList;
+ if (p != NULL) {
+ FreeList = p->FreeNext;
}
-
- // We've detached the list. The list in-hand is now
- // local to this thread. This thread can operate on the
- // list without risk of interference from other threads.
- // 2: Extract -- pop the 1st element from the list.
- Parker * List = p->FreeNext ;
- if (List == NULL) break ;
- for (;;) {
- // 3: Try to reattach the residual list
- guarantee (List != NULL, "invariant") ;
- Parker * Arv = (Parker *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
- if (Arv == NULL) break ;
-
- // New nodes arrived. Try to detach the recent arrivals.
- if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
- continue ;
- }
- guarantee (Arv != NULL, "invariant") ;
- // 4: Merge Arv into List
- Parker * Tail = List ;
- while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
- Tail->FreeNext = Arv ;
- }
- break ;
}
+ Thread::SpinRelease(&ListLock);
if (p != NULL) {
guarantee (p->AssociatedWith == NULL, "invariant") ;
} else {
// Do this the hard way -- materialize a new Parker..
- // In rare cases an allocating thread might detach
- // a long list -- installing null into FreeList --and
- // then stall. Another thread calling Allocate() would see
- // FreeList == null and then invoke the ctor. In this case we
- // end up with more Parkers in circulation than we need, but
- // the race is rare and the outcome is benign.
- // Ideally, the # of extant Parkers is equal to the
- // maximum # of threads that existed at any one time.
- // Because of the race mentioned above, segments of the
- // freelist can be transiently inaccessible. At worst
- // we may end up with the # of Parkers in circulation
- // slightly above the ideal.
p = new Parker() ;
}
p->AssociatedWith = t ; // Associate p with t
@@ -227,11 +157,12 @@
guarantee (p->AssociatedWith != NULL, "invariant") ;
guarantee (p->FreeNext == NULL , "invariant") ;
p->AssociatedWith = NULL ;
- for (;;) {
- // Push p onto FreeList
- Parker * List = FreeList ;
- p->FreeNext = List ;
- if (Atomic::cmpxchg_ptr (p, &FreeList, List) == List) break ;
+
+ Thread::SpinAcquire(&ListLock, "ParkerFreeListRelease");
+ {
+ p->FreeNext = FreeList;
+ FreeList = p;
}
+ Thread::SpinRelease(&ListLock);
}