1 /*
   2  * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
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  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "runtime/thread.hpp"
  27 
  28 
  29 
  30 // Lifecycle management for TSM ParkEvents.
  31 // ParkEvents are type-stable (TSM).
  32 // In our particular implementation they happen to be immortal.
  33 //
  34 // We manage concurrency on the FreeList with a CAS-based
  35 // detach-modify-reattach idiom that avoids the ABA problems
  36 // that would otherwise be present in a simple CAS-based
  37 // push-pop implementation.   (push-one and pop-all)
  38 //
  39 // Caveat: Allocate() and Release() may be called from threads
  40 // other than the thread associated with the Event!
  41 // If we need to call Allocate() when running as the thread in
  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 consolidate 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