42 // question then look for the PD calls to initialize native TLS.
43 // Native TLS (Win32/Linux/Solaris) can only be initialized or
44 // accessed by the associated thread.
45 // See also pd_initialize().
46 //
47 // Note that we could defer associating a ParkEvent with a thread
48 // until the 1st time the thread calls park(). unpark() calls to
49 // an unprovisioned thread would be ignored. The first park() call
50 // for a thread would allocate and associate a ParkEvent and return
51 // immediately.
52
53 volatile int ParkEvent::ListLock = 0 ;
54 ParkEvent * volatile ParkEvent::FreeList = NULL ;
55
56 ParkEvent * ParkEvent::Allocate (Thread * t) {
57 // In rare cases -- JVM_RawMonitor* operations -- we can find t == null.
58 ParkEvent * ev ;
59
60 // Start by trying to recycle an existing but unassociated
61 // ParkEvent from the global free list.
62 for (;;) {
63 ev = FreeList ;
64 if (ev == NULL) break ;
65 // 1: Detach - sequester or privatize the list
66 // Tantamount to ev = Swap (&FreeList, NULL)
67 if (Atomic::cmpxchg_ptr (NULL, &FreeList, ev) != ev) {
68 continue ;
69 }
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 }
95
96 if (ev != NULL) {
97 guarantee (ev->AssociatedWith == NULL, "invariant") ;
98 } else {
99 // 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 () ;
115 guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ;
116 }
117 ev->reset() ; // courtesy to caller
118 ev->AssociatedWith = t ; // Associate ev with t
119 ev->FreeNext = NULL ;
120 return ev ;
121 }
122
123 void ParkEvent::Release (ParkEvent * ev) {
124 if (ev == NULL) return ;
125 guarantee (ev->FreeNext == NULL , "invariant") ;
126 ev->AssociatedWith = NULL ;
127 for (;;) {
128 // Push ev onto FreeList
129 // The mechanism is "half" lock-free.
130 ParkEvent * List = FreeList ;
131 ev->FreeNext = List ;
132 if (Atomic::cmpxchg_ptr (ev, &FreeList, List) == List) break ;
133 }
134 }
135
136 // Override operator new and delete so we can ensure that the
137 // least significant byte of ParkEvent addresses is 0.
138 // Beware that excessive address alignment is undesirable
139 // as it can result in D$ index usage imbalance as
140 // well as bank access imbalance on Niagara-like platforms,
141 // although Niagara's hash function should help.
142
143 void * ParkEvent::operator new (size_t sz) throw() {
144 return (void *) ((intptr_t (AllocateHeap(sz + 256, mtInternal, CALLER_PC)) + 256) & -256) ;
145 }
146
147 void ParkEvent::operator delete (void * a) {
148 // ParkEvents are type-stable and immortal ...
149 ShouldNotReachHere();
150 }
151
152
153 // 6399321 As a temporary measure we copied & modified the ParkEvent::
154 // allocate() and release() code for use by Parkers. The Parker:: forms
155 // will eventually be removed as we consolide and shift over to ParkEvents
156 // for both builtin synchronization and JSR166 operations.
157
158 volatile int Parker::ListLock = 0 ;
159 Parker * volatile Parker::FreeList = NULL ;
160
161 Parker * Parker::Allocate (JavaThread * t) {
162 guarantee (t != NULL, "invariant") ;
163 Parker * p ;
164
165 // Start by trying to recycle an existing but unassociated
166 // Parker from the global free list.
167 for (;;) {
168 p = FreeList ;
169 if (p == NULL) break ;
170 // 1: Detach
171 // Tantamount to p = Swap (&FreeList, NULL)
172 if (Atomic::cmpxchg_ptr (NULL, &FreeList, p) != p) {
173 continue ;
174 }
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 }
200
201 if (p != NULL) {
202 guarantee (p->AssociatedWith == NULL, "invariant") ;
203 } else {
204 // 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() ;
218 }
219 p->AssociatedWith = t ; // Associate p with t
220 p->FreeNext = NULL ;
221 return p ;
222 }
223
224
225 void Parker::Release (Parker * p) {
226 if (p == NULL) return ;
227 guarantee (p->AssociatedWith != NULL, "invariant") ;
228 guarantee (p->FreeNext == NULL , "invariant") ;
229 p->AssociatedWith = NULL ;
230 for (;;) {
231 // Push p onto FreeList
232 Parker * List = FreeList ;
233 p->FreeNext = List ;
234 if (Atomic::cmpxchg_ptr (p, &FreeList, List) == List) break ;
235 }
236 }
237
|
42 // question then look for the PD calls to initialize native TLS.
43 // Native TLS (Win32/Linux/Solaris) can only be initialized or
44 // accessed by the associated thread.
45 // See also pd_initialize().
46 //
47 // Note that we could defer associating a ParkEvent with a thread
48 // until the 1st time the thread calls park(). unpark() calls to
49 // an unprovisioned thread would be ignored. The first park() call
50 // for a thread would allocate and associate a ParkEvent and return
51 // immediately.
52
53 volatile int ParkEvent::ListLock = 0 ;
54 ParkEvent * volatile ParkEvent::FreeList = NULL ;
55
56 ParkEvent * ParkEvent::Allocate (Thread * t) {
57 // In rare cases -- JVM_RawMonitor* operations -- we can find t == null.
58 ParkEvent * ev ;
59
60 // Start by trying to recycle an existing but unassociated
61 // ParkEvent from the global free list.
62 // Using a spin lock since we are part of the mutex impl.
63 // 8028280: using concurrent free list without memory management can leak
64 // pretty badly it turns out.
65 Thread::SpinAcquire(&ListLock, "ParkEventFreeListAllocate");
66 {
67 ev = FreeList;
68 if (ev != NULL) {
69 FreeList = ev->FreeNext;
70 }
71 }
72 Thread::SpinRelease(&ListLock);
73
74 if (ev != NULL) {
75 guarantee (ev->AssociatedWith == NULL, "invariant") ;
76 } else {
77 // Do this the hard way -- materialize a new ParkEvent.
78 ev = new ParkEvent () ;
79 guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ;
80 }
81 ev->reset() ; // courtesy to caller
82 ev->AssociatedWith = t ; // Associate ev with t
83 ev->FreeNext = NULL ;
84 return ev ;
85 }
86
87 void ParkEvent::Release (ParkEvent * ev) {
88 if (ev == NULL) return ;
89 guarantee (ev->FreeNext == NULL , "invariant") ;
90 ev->AssociatedWith = NULL ;
91 // Note that if we didn't have the TSM/immortal constraint, then
92 // when reattaching we could trim the list.
93 Thread::SpinAcquire(&ListLock, "ParkEventFreeListRelease");
94 {
95 ev->FreeNext = FreeList;
96 FreeList = ev;
97 }
98 Thread::SpinRelease(&ListLock);
99 }
100
101 // Override operator new and delete so we can ensure that the
102 // least significant byte of ParkEvent addresses is 0.
103 // Beware that excessive address alignment is undesirable
104 // as it can result in D$ index usage imbalance as
105 // well as bank access imbalance on Niagara-like platforms,
106 // although Niagara's hash function should help.
107
108 void * ParkEvent::operator new (size_t sz) throw() {
109 return (void *) ((intptr_t (AllocateHeap(sz + 256, mtInternal, CALLER_PC)) + 256) & -256) ;
110 }
111
112 void ParkEvent::operator delete (void * a) {
113 // ParkEvents are type-stable and immortal ...
114 ShouldNotReachHere();
115 }
116
117
118 // 6399321 As a temporary measure we copied & modified the ParkEvent::
119 // allocate() and release() code for use by Parkers. The Parker:: forms
120 // will eventually be removed as we consolide and shift over to ParkEvents
121 // for both builtin synchronization and JSR166 operations.
122
123 volatile int Parker::ListLock = 0 ;
124 Parker * volatile Parker::FreeList = NULL ;
125
126 Parker * Parker::Allocate (JavaThread * t) {
127 guarantee (t != NULL, "invariant") ;
128 Parker * p ;
129
130 // Start by trying to recycle an existing but unassociated
131 // Parker from the global free list.
132 // 8028280: using concurrent free list without memory management can leak
133 // pretty badly it turns out.
134 Thread::SpinAcquire(&ListLock, "ParkerFreeListAllocate");
135 {
136 p = FreeList;
137 if (p != NULL) {
138 FreeList = p->FreeNext;
139 }
140 }
141 Thread::SpinRelease(&ListLock);
142
143 if (p != NULL) {
144 guarantee (p->AssociatedWith == NULL, "invariant") ;
145 } else {
146 // Do this the hard way -- materialize a new Parker..
147 p = new Parker() ;
148 }
149 p->AssociatedWith = t ; // Associate p with t
150 p->FreeNext = NULL ;
151 return p ;
152 }
153
154
155 void Parker::Release (Parker * p) {
156 if (p == NULL) return ;
157 guarantee (p->AssociatedWith != NULL, "invariant") ;
158 guarantee (p->FreeNext == NULL , "invariant") ;
159 p->AssociatedWith = NULL ;
160
161 Thread::SpinAcquire(&ListLock, "ParkerFreeListRelease");
162 {
163 p->FreeNext = FreeList;
164 FreeList = p;
165 }
166 Thread::SpinRelease(&ListLock);
167 }
168
|