1.1 --- a/src/share/vm/runtime/park.cpp Fri Feb 14 09:50:17 2014 -0800
1.2 +++ b/src/share/vm/runtime/park.cpp Fri Jan 24 09:28:47 2014 +0100
1.3 @@ -59,58 +59,22 @@
1.4
1.5 // Start by trying to recycle an existing but unassociated
1.6 // ParkEvent from the global free list.
1.7 - for (;;) {
1.8 - ev = FreeList ;
1.9 - if (ev == NULL) break ;
1.10 - // 1: Detach - sequester or privatize the list
1.11 - // Tantamount to ev = Swap (&FreeList, NULL)
1.12 - if (Atomic::cmpxchg_ptr (NULL, &FreeList, ev) != ev) {
1.13 - continue ;
1.14 + // Using a spin lock since we are part of the mutex impl.
1.15 + // 8028280: using concurrent free list without memory management can leak
1.16 + // pretty badly it turns out.
1.17 + Thread::SpinAcquire(&ListLock, "ParkEventFreeListAllocate");
1.18 + {
1.19 + ev = FreeList;
1.20 + if (ev != NULL) {
1.21 + FreeList = ev->FreeNext;
1.22 }
1.23 -
1.24 - // We've detached the list. The list in-hand is now
1.25 - // local to this thread. This thread can operate on the
1.26 - // list without risk of interference from other threads.
1.27 - // 2: Extract -- pop the 1st element from the list.
1.28 - ParkEvent * List = ev->FreeNext ;
1.29 - if (List == NULL) break ;
1.30 - for (;;) {
1.31 - // 3: Try to reattach the residual list
1.32 - guarantee (List != NULL, "invariant") ;
1.33 - ParkEvent * Arv = (ParkEvent *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
1.34 - if (Arv == NULL) break ;
1.35 -
1.36 - // New nodes arrived. Try to detach the recent arrivals.
1.37 - if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
1.38 - continue ;
1.39 - }
1.40 - guarantee (Arv != NULL, "invariant") ;
1.41 - // 4: Merge Arv into List
1.42 - ParkEvent * Tail = List ;
1.43 - while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
1.44 - Tail->FreeNext = Arv ;
1.45 - }
1.46 - break ;
1.47 }
1.48 + Thread::SpinRelease(&ListLock);
1.49
1.50 if (ev != NULL) {
1.51 guarantee (ev->AssociatedWith == NULL, "invariant") ;
1.52 } else {
1.53 // Do this the hard way -- materialize a new ParkEvent.
1.54 - // In rare cases an allocating thread might detach a long list --
1.55 - // installing null into FreeList -- and then stall or be obstructed.
1.56 - // A 2nd thread calling Allocate() would see FreeList == null.
1.57 - // The list held privately by the 1st thread is unavailable to the 2nd thread.
1.58 - // In that case the 2nd thread would have to materialize a new ParkEvent,
1.59 - // even though free ParkEvents existed in the system. In this case we end up
1.60 - // with more ParkEvents in circulation than we need, but the race is
1.61 - // rare and the outcome is benign. Ideally, the # of extant ParkEvents
1.62 - // is equal to the maximum # of threads that existed at any one time.
1.63 - // Because of the race mentioned above, segments of the freelist
1.64 - // can be transiently inaccessible. At worst we may end up with the
1.65 - // # of ParkEvents in circulation slightly above the ideal.
1.66 - // Note that if we didn't have the TSM/immortal constraint, then
1.67 - // when reattaching, above, we could trim the list.
1.68 ev = new ParkEvent () ;
1.69 guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ;
1.70 }
1.71 @@ -124,13 +88,14 @@
1.72 if (ev == NULL) return ;
1.73 guarantee (ev->FreeNext == NULL , "invariant") ;
1.74 ev->AssociatedWith = NULL ;
1.75 - for (;;) {
1.76 - // Push ev onto FreeList
1.77 - // The mechanism is "half" lock-free.
1.78 - ParkEvent * List = FreeList ;
1.79 - ev->FreeNext = List ;
1.80 - if (Atomic::cmpxchg_ptr (ev, &FreeList, List) == List) break ;
1.81 + // Note that if we didn't have the TSM/immortal constraint, then
1.82 + // when reattaching we could trim the list.
1.83 + Thread::SpinAcquire(&ListLock, "ParkEventFreeListRelease");
1.84 + {
1.85 + ev->FreeNext = FreeList;
1.86 + FreeList = ev;
1.87 }
1.88 + Thread::SpinRelease(&ListLock);
1.89 }
1.90
1.91 // Override operator new and delete so we can ensure that the
1.92 @@ -164,56 +129,21 @@
1.93
1.94 // Start by trying to recycle an existing but unassociated
1.95 // Parker from the global free list.
1.96 - for (;;) {
1.97 - p = FreeList ;
1.98 - if (p == NULL) break ;
1.99 - // 1: Detach
1.100 - // Tantamount to p = Swap (&FreeList, NULL)
1.101 - if (Atomic::cmpxchg_ptr (NULL, &FreeList, p) != p) {
1.102 - continue ;
1.103 + // 8028280: using concurrent free list without memory management can leak
1.104 + // pretty badly it turns out.
1.105 + Thread::SpinAcquire(&ListLock, "ParkerFreeListAllocate");
1.106 + {
1.107 + p = FreeList;
1.108 + if (p != NULL) {
1.109 + FreeList = p->FreeNext;
1.110 }
1.111 -
1.112 - // We've detached the list. The list in-hand is now
1.113 - // local to this thread. This thread can operate on the
1.114 - // list without risk of interference from other threads.
1.115 - // 2: Extract -- pop the 1st element from the list.
1.116 - Parker * List = p->FreeNext ;
1.117 - if (List == NULL) break ;
1.118 - for (;;) {
1.119 - // 3: Try to reattach the residual list
1.120 - guarantee (List != NULL, "invariant") ;
1.121 - Parker * Arv = (Parker *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
1.122 - if (Arv == NULL) break ;
1.123 -
1.124 - // New nodes arrived. Try to detach the recent arrivals.
1.125 - if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
1.126 - continue ;
1.127 - }
1.128 - guarantee (Arv != NULL, "invariant") ;
1.129 - // 4: Merge Arv into List
1.130 - Parker * Tail = List ;
1.131 - while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
1.132 - Tail->FreeNext = Arv ;
1.133 - }
1.134 - break ;
1.135 }
1.136 + Thread::SpinRelease(&ListLock);
1.137
1.138 if (p != NULL) {
1.139 guarantee (p->AssociatedWith == NULL, "invariant") ;
1.140 } else {
1.141 // Do this the hard way -- materialize a new Parker..
1.142 - // In rare cases an allocating thread might detach
1.143 - // a long list -- installing null into FreeList --and
1.144 - // then stall. Another thread calling Allocate() would see
1.145 - // FreeList == null and then invoke the ctor. In this case we
1.146 - // end up with more Parkers in circulation than we need, but
1.147 - // the race is rare and the outcome is benign.
1.148 - // Ideally, the # of extant Parkers is equal to the
1.149 - // maximum # of threads that existed at any one time.
1.150 - // Because of the race mentioned above, segments of the
1.151 - // freelist can be transiently inaccessible. At worst
1.152 - // we may end up with the # of Parkers in circulation
1.153 - // slightly above the ideal.
1.154 p = new Parker() ;
1.155 }
1.156 p->AssociatedWith = t ; // Associate p with t
1.157 @@ -227,11 +157,12 @@
1.158 guarantee (p->AssociatedWith != NULL, "invariant") ;
1.159 guarantee (p->FreeNext == NULL , "invariant") ;
1.160 p->AssociatedWith = NULL ;
1.161 - for (;;) {
1.162 - // Push p onto FreeList
1.163 - Parker * List = FreeList ;
1.164 - p->FreeNext = List ;
1.165 - if (Atomic::cmpxchg_ptr (p, &FreeList, List) == List) break ;
1.166 +
1.167 + Thread::SpinAcquire(&ListLock, "ParkerFreeListRelease");
1.168 + {
1.169 + p->FreeNext = FreeList;
1.170 + FreeList = p;
1.171 }
1.172 + Thread::SpinRelease(&ListLock);
1.173 }
1.174
