1878
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1 /*
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2 * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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20 * or visit www.oracle.com if you need additional information or have any
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21 * questions.
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22 *
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23 */
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24
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1972
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25 #include "precompiled.hpp"
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26 #include "runtime/thread.hpp"
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1878
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27
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28
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29
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30 // Lifecycle management for TSM ParkEvents.
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31 // ParkEvents are type-stable (TSM).
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32 // In our particular implementation they happen to be immortal.
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33 //
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34 // We manage concurrency on the FreeList with a CAS-based
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35 // detach-modify-reattach idiom that avoids the ABA problems
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36 // that would otherwise be present in a simple CAS-based
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37 // push-pop implementation. (push-one and pop-all)
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38 //
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39 // Caveat: Allocate() and Release() may be called from threads
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40 // other than the thread associated with the Event!
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41 // If we need to call Allocate() when running as the thread in
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42 // question then look for the PD calls to initialize native TLS.
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43 // Native TLS (Win32/Linux/Solaris) can only be initialized or
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44 // accessed by the associated thread.
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45 // See also pd_initialize().
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46 //
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47 // Note that we could defer associating a ParkEvent with a thread
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48 // until the 1st time the thread calls park(). unpark() calls to
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49 // an unprovisioned thread would be ignored. The first park() call
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50 // for a thread would allocate and associate a ParkEvent and return
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51 // immediately.
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52
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53 volatile int ParkEvent::ListLock = 0 ;
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54 ParkEvent * volatile ParkEvent::FreeList = NULL ;
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55
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56 ParkEvent * ParkEvent::Allocate (Thread * t) {
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57 // In rare cases -- JVM_RawMonitor* operations -- we can find t == null.
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58 ParkEvent * ev ;
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59
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60 // Start by trying to recycle an existing but unassociated
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61 // ParkEvent from the global free list.
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62 for (;;) {
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63 ev = FreeList ;
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64 if (ev == NULL) break ;
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65 // 1: Detach - sequester or privatize the list
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66 // Tantamount to ev = Swap (&FreeList, NULL)
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67 if (Atomic::cmpxchg_ptr (NULL, &FreeList, ev) != ev) {
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68 continue ;
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69 }
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70
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71 // We've detached the list. The list in-hand is now
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72 // local to this thread. This thread can operate on the
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73 // list without risk of interference from other threads.
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74 // 2: Extract -- pop the 1st element from the list.
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75 ParkEvent * List = ev->FreeNext ;
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76 if (List == NULL) break ;
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77 for (;;) {
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78 // 3: Try to reattach the residual list
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79 guarantee (List != NULL, "invariant") ;
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80 ParkEvent * Arv = (ParkEvent *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
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81 if (Arv == NULL) break ;
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82
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83 // New nodes arrived. Try to detach the recent arrivals.
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84 if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
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85 continue ;
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86 }
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87 guarantee (Arv != NULL, "invariant") ;
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88 // 4: Merge Arv into List
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89 ParkEvent * Tail = List ;
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90 while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
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91 Tail->FreeNext = Arv ;
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92 }
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93 break ;
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94 }
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95
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96 if (ev != NULL) {
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97 guarantee (ev->AssociatedWith == NULL, "invariant") ;
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98 } else {
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99 // Do this the hard way -- materialize a new ParkEvent.
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100 // In rare cases an allocating thread might detach a long list --
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101 // installing null into FreeList -- and then stall or be obstructed.
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102 // A 2nd thread calling Allocate() would see FreeList == null.
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103 // The list held privately by the 1st thread is unavailable to the 2nd thread.
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104 // In that case the 2nd thread would have to materialize a new ParkEvent,
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105 // even though free ParkEvents existed in the system. In this case we end up
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106 // with more ParkEvents in circulation than we need, but the race is
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107 // rare and the outcome is benign. Ideally, the # of extant ParkEvents
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108 // is equal to the maximum # of threads that existed at any one time.
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109 // Because of the race mentioned above, segments of the freelist
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110 // can be transiently inaccessible. At worst we may end up with the
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111 // # of ParkEvents in circulation slightly above the ideal.
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112 // Note that if we didn't have the TSM/immortal constraint, then
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113 // when reattaching, above, we could trim the list.
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114 ev = new ParkEvent () ;
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115 guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ;
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116 }
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117 ev->reset() ; // courtesy to caller
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118 ev->AssociatedWith = t ; // Associate ev with t
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119 ev->FreeNext = NULL ;
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120 return ev ;
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121 }
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122
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123 void ParkEvent::Release (ParkEvent * ev) {
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124 if (ev == NULL) return ;
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125 guarantee (ev->FreeNext == NULL , "invariant") ;
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126 ev->AssociatedWith = NULL ;
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127 for (;;) {
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128 // Push ev onto FreeList
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129 // The mechanism is "half" lock-free.
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130 ParkEvent * List = FreeList ;
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131 ev->FreeNext = List ;
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132 if (Atomic::cmpxchg_ptr (ev, &FreeList, List) == List) break ;
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133 }
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134 }
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135
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136 // Override operator new and delete so we can ensure that the
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137 // least significant byte of ParkEvent addresses is 0.
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138 // Beware that excessive address alignment is undesirable
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139 // as it can result in D$ index usage imbalance as
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140 // well as bank access imbalance on Niagara-like platforms,
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141 // although Niagara's hash function should help.
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142
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143 void * ParkEvent::operator new (size_t sz) {
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144 return (void *) ((intptr_t (CHeapObj::operator new (sz + 256)) + 256) & -256) ;
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145 }
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146
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147 void ParkEvent::operator delete (void * a) {
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148 // ParkEvents are type-stable and immortal ...
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149 ShouldNotReachHere();
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150 }
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151
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152
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153 // 6399321 As a temporary measure we copied & modified the ParkEvent::
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154 // allocate() and release() code for use by Parkers. The Parker:: forms
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155 // will eventually be removed as we consolide and shift over to ParkEvents
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156 // for both builtin synchronization and JSR166 operations.
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157
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158 volatile int Parker::ListLock = 0 ;
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159 Parker * volatile Parker::FreeList = NULL ;
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160
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161 Parker * Parker::Allocate (JavaThread * t) {
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162 guarantee (t != NULL, "invariant") ;
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163 Parker * p ;
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164
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165 // Start by trying to recycle an existing but unassociated
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166 // Parker from the global free list.
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167 for (;;) {
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168 p = FreeList ;
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169 if (p == NULL) break ;
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170 // 1: Detach
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171 // Tantamount to p = Swap (&FreeList, NULL)
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172 if (Atomic::cmpxchg_ptr (NULL, &FreeList, p) != p) {
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173 continue ;
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174 }
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175
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176 // We've detached the list. The list in-hand is now
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177 // local to this thread. This thread can operate on the
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178 // list without risk of interference from other threads.
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179 // 2: Extract -- pop the 1st element from the list.
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180 Parker * List = p->FreeNext ;
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181 if (List == NULL) break ;
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182 for (;;) {
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183 // 3: Try to reattach the residual list
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184 guarantee (List != NULL, "invariant") ;
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185 Parker * Arv = (Parker *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
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186 if (Arv == NULL) break ;
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187
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188 // New nodes arrived. Try to detach the recent arrivals.
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189 if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
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190 continue ;
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191 }
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192 guarantee (Arv != NULL, "invariant") ;
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193 // 4: Merge Arv into List
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194 Parker * Tail = List ;
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195 while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
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196 Tail->FreeNext = Arv ;
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197 }
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198 break ;
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199 }
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200
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201 if (p != NULL) {
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202 guarantee (p->AssociatedWith == NULL, "invariant") ;
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203 } else {
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204 // Do this the hard way -- materialize a new Parker..
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205 // In rare cases an allocating thread might detach
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206 // a long list -- installing null into FreeList --and
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207 // then stall. Another thread calling Allocate() would see
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208 // FreeList == null and then invoke the ctor. In this case we
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209 // end up with more Parkers in circulation than we need, but
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210 // the race is rare and the outcome is benign.
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211 // Ideally, the # of extant Parkers is equal to the
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212 // maximum # of threads that existed at any one time.
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213 // Because of the race mentioned above, segments of the
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214 // freelist can be transiently inaccessible. At worst
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215 // we may end up with the # of Parkers in circulation
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216 // slightly above the ideal.
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217 p = new Parker() ;
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218 }
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219 p->AssociatedWith = t ; // Associate p with t
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220 p->FreeNext = NULL ;
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221 return p ;
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222 }
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223
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224
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225 void Parker::Release (Parker * p) {
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226 if (p == NULL) return ;
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227 guarantee (p->AssociatedWith != NULL, "invariant") ;
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228 guarantee (p->FreeNext == NULL , "invariant") ;
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229 p->AssociatedWith = NULL ;
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230 for (;;) {
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231 // Push p onto FreeList
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232 Parker * List = FreeList ;
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233 p->FreeNext = List ;
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234 if (Atomic::cmpxchg_ptr (p, &FreeList, List) == List) break ;
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235 }
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236 }
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237
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