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comparison src/share/vm/runtime/park.cpp @ 14518:d8041d695d19

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Merged with jdk9/dev/hotspot changeset 3812c088b945
author twisti
date Tue, 11 Mar 2014 18:45:59 -0700
parents 2c95095271e9
children 4ca6dc0799b6
comparison
equal deleted inserted replaced
14141:f97c5ec83832 14518:d8041d695d19
57 // In rare cases -- JVM_RawMonitor* operations -- we can find t == null. 57 // In rare cases -- JVM_RawMonitor* operations -- we can find t == null.
58 ParkEvent * ev ; 58 ParkEvent * ev ;
59 59
60 // Start by trying to recycle an existing but unassociated 60 // Start by trying to recycle an existing but unassociated
61 // ParkEvent from the global free list. 61 // ParkEvent from the global free list.
62 for (;;) { 62 // Using a spin lock since we are part of the mutex impl.
63 ev = FreeList ; 63 // 8028280: using concurrent free list without memory management can leak
64 if (ev == NULL) break ; 64 // pretty badly it turns out.
65 // 1: Detach - sequester or privatize the list 65 Thread::SpinAcquire(&ListLock, "ParkEventFreeListAllocate");
66 // Tantamount to ev = Swap (&FreeList, NULL) 66 {
67 if (Atomic::cmpxchg_ptr (NULL, &FreeList, ev) != ev) { 67 ev = FreeList;
68 continue ; 68 if (ev != NULL) {
69 FreeList = ev->FreeNext;
69 } 70 }
70
71 // We've detached the list. The list in-hand is now
72 // local to this thread. This thread can operate on the
73 // list without risk of interference from other threads.
74 // 2: Extract -- pop the 1st element from the list.
75 ParkEvent * List = ev->FreeNext ;
76 if (List == NULL) break ;
77 for (;;) {
78 // 3: Try to reattach the residual list
79 guarantee (List != NULL, "invariant") ;
80 ParkEvent * Arv = (ParkEvent *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
81 if (Arv == NULL) break ;
82
83 // New nodes arrived. Try to detach the recent arrivals.
84 if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
85 continue ;
86 }
87 guarantee (Arv != NULL, "invariant") ;
88 // 4: Merge Arv into List
89 ParkEvent * Tail = List ;
90 while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
91 Tail->FreeNext = Arv ;
92 }
93 break ;
94 } 71 }
72 Thread::SpinRelease(&ListLock);
95 73
96 if (ev != NULL) { 74 if (ev != NULL) {
97 guarantee (ev->AssociatedWith == NULL, "invariant") ; 75 guarantee (ev->AssociatedWith == NULL, "invariant") ;
98 } else { 76 } else {
99 // Do this the hard way -- materialize a new ParkEvent. 77 // Do this the hard way -- materialize a new ParkEvent.
100 // In rare cases an allocating thread might detach a long list --
101 // installing null into FreeList -- and then stall or be obstructed.
102 // A 2nd thread calling Allocate() would see FreeList == null.
103 // The list held privately by the 1st thread is unavailable to the 2nd thread.
104 // In that case the 2nd thread would have to materialize a new ParkEvent,
105 // even though free ParkEvents existed in the system. In this case we end up
106 // with more ParkEvents in circulation than we need, but the race is
107 // rare and the outcome is benign. Ideally, the # of extant ParkEvents
108 // is equal to the maximum # of threads that existed at any one time.
109 // Because of the race mentioned above, segments of the freelist
110 // can be transiently inaccessible. At worst we may end up with the
111 // # of ParkEvents in circulation slightly above the ideal.
112 // Note that if we didn't have the TSM/immortal constraint, then
113 // when reattaching, above, we could trim the list.
114 ev = new ParkEvent () ; 78 ev = new ParkEvent () ;
115 guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ; 79 guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ;
116 } 80 }
117 ev->reset() ; // courtesy to caller 81 ev->reset() ; // courtesy to caller
118 ev->AssociatedWith = t ; // Associate ev with t 82 ev->AssociatedWith = t ; // Associate ev with t
122 86
123 void ParkEvent::Release (ParkEvent * ev) { 87 void ParkEvent::Release (ParkEvent * ev) {
124 if (ev == NULL) return ; 88 if (ev == NULL) return ;
125 guarantee (ev->FreeNext == NULL , "invariant") ; 89 guarantee (ev->FreeNext == NULL , "invariant") ;
126 ev->AssociatedWith = NULL ; 90 ev->AssociatedWith = NULL ;
127 for (;;) { 91 // Note that if we didn't have the TSM/immortal constraint, then
128 // Push ev onto FreeList 92 // when reattaching we could trim the list.
129 // The mechanism is "half" lock-free. 93 Thread::SpinAcquire(&ListLock, "ParkEventFreeListRelease");
130 ParkEvent * List = FreeList ; 94 {
131 ev->FreeNext = List ; 95 ev->FreeNext = FreeList;
132 if (Atomic::cmpxchg_ptr (ev, &FreeList, List) == List) break ; 96 FreeList = ev;
133 } 97 }
98 Thread::SpinRelease(&ListLock);
134 } 99 }
135 100
136 // Override operator new and delete so we can ensure that the 101 // Override operator new and delete so we can ensure that the
137 // least significant byte of ParkEvent addresses is 0. 102 // least significant byte of ParkEvent addresses is 0.
138 // Beware that excessive address alignment is undesirable 103 // Beware that excessive address alignment is undesirable
150 } 115 }
151 116
152 117
153 // 6399321 As a temporary measure we copied & modified the ParkEvent:: 118 // 6399321 As a temporary measure we copied & modified the ParkEvent::
154 // allocate() and release() code for use by Parkers. The Parker:: forms 119 // allocate() and release() code for use by Parkers. The Parker:: forms
155 // will eventually be removed as we consolide and shift over to ParkEvents 120 // will eventually be removed as we consolidate and shift over to ParkEvents
156 // for both builtin synchronization and JSR166 operations. 121 // for both builtin synchronization and JSR166 operations.
157 122
158 volatile int Parker::ListLock = 0 ; 123 volatile int Parker::ListLock = 0 ;
159 Parker * volatile Parker::FreeList = NULL ; 124 Parker * volatile Parker::FreeList = NULL ;
160 125
162 guarantee (t != NULL, "invariant") ; 127 guarantee (t != NULL, "invariant") ;
163 Parker * p ; 128 Parker * p ;
164 129
165 // Start by trying to recycle an existing but unassociated 130 // Start by trying to recycle an existing but unassociated
166 // Parker from the global free list. 131 // Parker from the global free list.
167 for (;;) { 132 // 8028280: using concurrent free list without memory management can leak
168 p = FreeList ; 133 // pretty badly it turns out.
169 if (p == NULL) break ; 134 Thread::SpinAcquire(&ListLock, "ParkerFreeListAllocate");
170 // 1: Detach 135 {
171 // Tantamount to p = Swap (&FreeList, NULL) 136 p = FreeList;
172 if (Atomic::cmpxchg_ptr (NULL, &FreeList, p) != p) { 137 if (p != NULL) {
173 continue ; 138 FreeList = p->FreeNext;
174 } 139 }
175
176 // We've detached the list. The list in-hand is now
177 // local to this thread. This thread can operate on the
178 // list without risk of interference from other threads.
179 // 2: Extract -- pop the 1st element from the list.
180 Parker * List = p->FreeNext ;
181 if (List == NULL) break ;
182 for (;;) {
183 // 3: Try to reattach the residual list
184 guarantee (List != NULL, "invariant") ;
185 Parker * Arv = (Parker *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
186 if (Arv == NULL) break ;
187
188 // New nodes arrived. Try to detach the recent arrivals.
189 if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
190 continue ;
191 }
192 guarantee (Arv != NULL, "invariant") ;
193 // 4: Merge Arv into List
194 Parker * Tail = List ;
195 while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
196 Tail->FreeNext = Arv ;
197 }
198 break ;
199 } 140 }
141 Thread::SpinRelease(&ListLock);
200 142
201 if (p != NULL) { 143 if (p != NULL) {
202 guarantee (p->AssociatedWith == NULL, "invariant") ; 144 guarantee (p->AssociatedWith == NULL, "invariant") ;
203 } else { 145 } else {
204 // Do this the hard way -- materialize a new Parker.. 146 // Do this the hard way -- materialize a new Parker..
205 // In rare cases an allocating thread might detach
206 // a long list -- installing null into FreeList --and
207 // then stall. Another thread calling Allocate() would see
208 // FreeList == null and then invoke the ctor. In this case we
209 // end up with more Parkers in circulation than we need, but
210 // the race is rare and the outcome is benign.
211 // Ideally, the # of extant Parkers is equal to the
212 // maximum # of threads that existed at any one time.
213 // Because of the race mentioned above, segments of the
214 // freelist can be transiently inaccessible. At worst
215 // we may end up with the # of Parkers in circulation
216 // slightly above the ideal.
217 p = new Parker() ; 147 p = new Parker() ;
218 } 148 }
219 p->AssociatedWith = t ; // Associate p with t 149 p->AssociatedWith = t ; // Associate p with t
220 p->FreeNext = NULL ; 150 p->FreeNext = NULL ;
221 return p ; 151 return p ;
225 void Parker::Release (Parker * p) { 155 void Parker::Release (Parker * p) {
226 if (p == NULL) return ; 156 if (p == NULL) return ;
227 guarantee (p->AssociatedWith != NULL, "invariant") ; 157 guarantee (p->AssociatedWith != NULL, "invariant") ;
228 guarantee (p->FreeNext == NULL , "invariant") ; 158 guarantee (p->FreeNext == NULL , "invariant") ;
229 p->AssociatedWith = NULL ; 159 p->AssociatedWith = NULL ;
230 for (;;) { 160
231 // Push p onto FreeList 161 Thread::SpinAcquire(&ListLock, "ParkerFreeListRelease");
232 Parker * List = FreeList ; 162 {
233 p->FreeNext = List ; 163 p->FreeNext = FreeList;
234 if (Atomic::cmpxchg_ptr (p, &FreeList, List) == List) break ; 164 FreeList = p;
235 } 165 }
166 Thread::SpinRelease(&ListLock);
236 } 167 }
237 168