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0
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1 /*
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2 * Copyright 2005 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 # include "incls/_precompiled.incl"
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26 # include "incls/_yieldingWorkgroup.cpp.incl"
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27
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28 // Forward declaration of classes declared here.
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29
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30 class GangWorker;
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31 class WorkData;
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32
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33 YieldingFlexibleWorkGang::YieldingFlexibleWorkGang(
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342
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34 const char* name, int workers, bool are_GC_task_threads) :
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35 AbstractWorkGang(name, are_GC_task_threads, false) {
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0
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36 // Save arguments.
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37 _total_workers = workers;
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38 assert(_total_workers > 0, "Must have more than 1 worker");
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39
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40 _yielded_workers = 0;
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41
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42 if (TraceWorkGang) {
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43 tty->print_cr("Constructing work gang %s with %d threads", name, workers);
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44 }
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45 _gang_workers = NEW_C_HEAP_ARRAY(GangWorker*, workers);
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46 assert(gang_workers() != NULL, "Failed to allocate gang workers");
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47 for (int worker = 0; worker < total_workers(); worker += 1) {
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48 YieldingFlexibleGangWorker* new_worker =
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49 new YieldingFlexibleGangWorker(this, worker);
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50 assert(new_worker != NULL, "Failed to allocate YieldingFlexibleGangWorker");
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51 _gang_workers[worker] = new_worker;
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52 if (new_worker == NULL || !os::create_thread(new_worker, os::pgc_thread))
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53 vm_exit_out_of_memory(0, "Cannot create worker GC thread. Out of system resources.");
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54 if (!DisableStartThread) {
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55 os::start_thread(new_worker);
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56 }
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57 }
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58 }
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59
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60 // Run a task; returns when the task is done, or the workers yield,
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61 // or the task is aborted, or the work gang is terminated via stop().
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62 // A task that has been yielded can be continued via this interface
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63 // by using the same task repeatedly as the argument to the call.
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64 // It is expected that the YieldingFlexibleGangTask carries the appropriate
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65 // continuation information used by workers to continue the task
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66 // from its last yield point. Thus, a completed task will return
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67 // immediately with no actual work having been done by the workers.
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68 /////////////////////
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69 // Implementatiuon notes: remove before checking XXX
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70 /*
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71 Each gang is working on a task at a certain time.
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72 Some subset of workers may have yielded and some may
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73 have finished their quota of work. Until this task has
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74 been completed, the workers are bound to that task.
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75 Once the task has been completed, the gang unbounds
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76 itself from the task.
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77
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78 The yielding work gang thus exports two invokation
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79 interfaces: run_task() and continue_task(). The
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80 first is used to initiate a new task and bind it
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81 to the workers; the second is used to continue an
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82 already bound task that has yielded. Upon completion
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83 the binding is released and a new binding may be
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84 created.
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85
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86 The shape of a yielding work gang is as follows:
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87
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88 Overseer invokes run_task(*task).
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89 Lock gang monitor
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90 Check that there is no existing binding for the gang
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91 If so, abort with an error
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92 Else, create a new binding of this gang to the given task
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93 Set number of active workers (as asked)
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94 Notify workers that work is ready to be done
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95 [the requisite # workers would then start up
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96 and do the task]
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97 Wait on the monitor until either
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98 all work is completed or the task has yielded
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99 -- this is normally done through
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100 yielded + completed == active
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101 [completed workers are rest to idle state by overseer?]
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102 return appropriate status to caller
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103
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104 Overseer invokes continue_task(*task),
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105 Lock gang monitor
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106 Check that task is the same as current binding
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107 If not, abort with an error
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108 Else, set the number of active workers as requested?
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109 Notify workers that they can continue from yield points
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110 New workers can also start up as required
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111 while satisfying the constraint that
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112 active + yielded does not exceed required number
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113 Wait (as above).
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114
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115 NOTE: In the above, for simplicity in a first iteration
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116 our gangs will be of fixed population and will not
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117 therefore be flexible work gangs, just yielding work
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118 gangs. Once this works well, we will in a second
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119 iteration.refinement introduce flexibility into
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120 the work gang.
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121
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122 NOTE: we can always create a new gang per each iteration
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123 in order to get the flexibility, but we will for now
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124 desist that simplified route.
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125
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126 */
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127 /////////////////////
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128 void YieldingFlexibleWorkGang::start_task(YieldingFlexibleGangTask* new_task) {
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129 MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);
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130 assert(task() == NULL, "Gang currently tied to a task");
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131 assert(new_task != NULL, "Null task");
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132 // Bind task to gang
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133 _task = new_task;
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134 new_task->set_gang(this); // Establish 2-way binding to support yielding
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135 _sequence_number++;
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136
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137 int requested_size = new_task->requested_size();
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138 assert(requested_size >= 0, "Should be non-negative");
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139 if (requested_size != 0) {
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140 _active_workers = MIN2(requested_size, total_workers());
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141 } else {
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142 _active_workers = total_workers();
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143 }
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144 new_task->set_actual_size(_active_workers);
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145
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146 assert(_started_workers == 0, "Tabula rasa non");
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147 assert(_finished_workers == 0, "Tabula rasa non");
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148 assert(_yielded_workers == 0, "Tabula rasa non");
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149 yielding_task()->set_status(ACTIVE);
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150
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151 // Wake up all the workers, the first few will get to work,
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152 // and the rest will go back to sleep
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153 monitor()->notify_all();
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154 wait_for_gang();
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155 }
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156
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157 void YieldingFlexibleWorkGang::wait_for_gang() {
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158
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159 assert(monitor()->owned_by_self(), "Data race");
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160 // Wait for task to complete or yield
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161 for (Status status = yielding_task()->status();
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162 status != COMPLETED && status != YIELDED && status != ABORTED;
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163 status = yielding_task()->status()) {
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164 assert(started_workers() <= active_workers(), "invariant");
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165 assert(finished_workers() <= active_workers(), "invariant");
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166 assert(yielded_workers() <= active_workers(), "invariant");
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167 monitor()->wait(Mutex::_no_safepoint_check_flag);
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168 }
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169 switch (yielding_task()->status()) {
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170 case COMPLETED:
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171 case ABORTED: {
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172 assert(finished_workers() == active_workers(), "Inconsistent status");
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173 assert(yielded_workers() == 0, "Invariant");
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174 reset(); // for next task; gang<->task binding released
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175 break;
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176 }
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177 case YIELDED: {
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178 assert(yielded_workers() > 0, "Invariant");
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179 assert(yielded_workers() + finished_workers() == active_workers(),
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180 "Inconsistent counts");
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181 break;
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182 }
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183 case ACTIVE:
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184 case INACTIVE:
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185 case COMPLETING:
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186 case YIELDING:
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187 case ABORTING:
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188 default:
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189 ShouldNotReachHere();
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190 }
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191 }
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192
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193 void YieldingFlexibleWorkGang::continue_task(
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194 YieldingFlexibleGangTask* gang_task) {
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195
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196 MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);
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197 assert(task() != NULL && task() == gang_task, "Incorrect usage");
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198 // assert(_active_workers == total_workers(), "For now");
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199 assert(_started_workers == _active_workers, "Precondition");
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200 assert(_yielded_workers > 0 && yielding_task()->status() == YIELDED,
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201 "Else why are we calling continue_task()");
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202 // Restart the yielded gang workers
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203 yielding_task()->set_status(ACTIVE);
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204 monitor()->notify_all();
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205 wait_for_gang();
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206 }
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207
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208 void YieldingFlexibleWorkGang::reset() {
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209 _started_workers = 0;
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210 _finished_workers = 0;
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211 _active_workers = 0;
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212 yielding_task()->set_gang(NULL);
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213 _task = NULL; // unbind gang from task
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214 }
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215
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216 void YieldingFlexibleWorkGang::yield() {
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217 assert(task() != NULL, "Inconsistency; should have task binding");
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218 MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);
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219 assert(yielded_workers() < active_workers(), "Consistency check");
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220 if (yielding_task()->status() == ABORTING) {
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221 // Do not yield; we need to abort as soon as possible
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222 // XXX NOTE: This can cause a performance pathology in the
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223 // current implementation in Mustang, as of today, and
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224 // pre-Mustang in that as soon as an overflow occurs,
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225 // yields will not be honoured. The right way to proceed
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226 // of course is to fix bug # TBF, so that abort's cause
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227 // us to return at each potential yield point.
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228 return;
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229 }
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230 if (++_yielded_workers + finished_workers() == active_workers()) {
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231 yielding_task()->set_status(YIELDED);
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232 monitor()->notify_all();
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233 } else {
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234 yielding_task()->set_status(YIELDING);
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235 }
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236
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237 while (true) {
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238 switch (yielding_task()->status()) {
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239 case YIELDING:
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240 case YIELDED: {
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241 monitor()->wait(Mutex::_no_safepoint_check_flag);
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242 break; // from switch
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243 }
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244 case ACTIVE:
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245 case ABORTING:
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246 case COMPLETING: {
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247 assert(_yielded_workers > 0, "Else why am i here?");
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248 _yielded_workers--;
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249 return;
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250 }
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251 case INACTIVE:
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252 case ABORTED:
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253 case COMPLETED:
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254 default: {
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255 ShouldNotReachHere();
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256 }
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257 }
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258 }
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259 // Only return is from inside switch statement above
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260 ShouldNotReachHere();
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261 }
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262
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263 void YieldingFlexibleWorkGang::abort() {
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264 assert(task() != NULL, "Inconsistency; should have task binding");
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265 MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);
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266 assert(yielded_workers() < active_workers(), "Consistency check");
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267 #ifndef PRODUCT
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268 switch (yielding_task()->status()) {
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269 // allowed states
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270 case ACTIVE:
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271 case ABORTING:
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272 case COMPLETING:
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273 case YIELDING:
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274 break;
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275 // not allowed states
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276 case INACTIVE:
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277 case ABORTED:
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278 case COMPLETED:
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279 case YIELDED:
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280 default:
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281 ShouldNotReachHere();
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282 }
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283 #endif // !PRODUCT
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284 Status prev_status = yielding_task()->status();
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285 yielding_task()->set_status(ABORTING);
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286 if (prev_status == YIELDING) {
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287 assert(yielded_workers() > 0, "Inconsistency");
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288 // At least one thread has yielded, wake it up
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289 // so it can go back to waiting stations ASAP.
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290 monitor()->notify_all();
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291 }
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292 }
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293
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294 ///////////////////////////////
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295 // YieldingFlexibleGangTask
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296 ///////////////////////////////
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297 void YieldingFlexibleGangTask::yield() {
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298 assert(gang() != NULL, "No gang to signal");
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299 gang()->yield();
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300 }
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301
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302 void YieldingFlexibleGangTask::abort() {
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303 assert(gang() != NULL, "No gang to signal");
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304 gang()->abort();
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305 }
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306
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307 ///////////////////////////////
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308 // YieldingFlexibleGangWorker
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309 ///////////////////////////////
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310 void YieldingFlexibleGangWorker::loop() {
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311 int previous_sequence_number = 0;
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312 Monitor* gang_monitor = gang()->monitor();
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313 MutexLockerEx ml(gang_monitor, Mutex::_no_safepoint_check_flag);
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314 WorkData data;
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315 int id;
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316 while (true) {
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317 // Check if there is work to do or if we have been asked
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318 // to terminate
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319 gang()->internal_worker_poll(&data);
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320 if (data.terminate()) {
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321 // We have been asked to terminate.
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322 assert(gang()->task() == NULL, "No task binding");
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323 // set_status(TERMINATED);
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324 return;
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325 } else if (data.task() != NULL &&
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326 data.sequence_number() != previous_sequence_number) {
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327 // There is work to be done.
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328 // First check if we need to become active or if there
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329 // are already the requisite number of workers
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330 if (gang()->started_workers() == yf_gang()->active_workers()) {
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331 // There are already enough workers, we do not need to
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332 // to run; fall through and wait on monitor.
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333 } else {
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334 // We need to pitch in and do the work.
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335 assert(gang()->started_workers() < yf_gang()->active_workers(),
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336 "Unexpected state");
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337 id = gang()->started_workers();
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338 gang()->internal_note_start();
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339 // Now, release the gang mutex and do the work.
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340 {
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341 MutexUnlockerEx mul(gang_monitor, Mutex::_no_safepoint_check_flag);
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342 data.task()->work(id); // This might include yielding
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343 }
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344 // Reacquire monitor and note completion of this worker
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345 gang()->internal_note_finish();
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346 // Update status of task based on whether all workers have
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347 // finished or some have yielded
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348 assert(data.task() == gang()->task(), "Confused task binding");
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349 if (gang()->finished_workers() == yf_gang()->active_workers()) {
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350 switch (data.yf_task()->status()) {
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351 case ABORTING: {
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352 data.yf_task()->set_status(ABORTED);
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353 break;
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354 }
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355 case ACTIVE:
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356 case COMPLETING: {
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357 data.yf_task()->set_status(COMPLETED);
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358 break;
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359 }
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360 default:
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361 ShouldNotReachHere();
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362 }
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363 gang_monitor->notify_all(); // Notify overseer
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364 } else { // at least one worker is still working or yielded
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365 assert(gang()->finished_workers() < yf_gang()->active_workers(),
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366 "Counts inconsistent");
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367 switch (data.yf_task()->status()) {
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368 case ACTIVE: {
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369 // first, but not only thread to complete
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370 data.yf_task()->set_status(COMPLETING);
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371 break;
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372 }
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373 case YIELDING: {
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374 if (gang()->finished_workers() + yf_gang()->yielded_workers()
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375 == yf_gang()->active_workers()) {
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376 data.yf_task()->set_status(YIELDED);
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377 gang_monitor->notify_all(); // notify overseer
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378 }
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379 break;
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380 }
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381 case ABORTING:
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382 case COMPLETING: {
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383 break; // nothing to do
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384 }
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385 default: // everything else: INACTIVE, YIELDED, ABORTED, COMPLETED
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386 ShouldNotReachHere();
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387 }
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388 }
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389 }
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390 }
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391 // Remember the sequence number
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392 previous_sequence_number = data.sequence_number();
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393 // Wait for more work
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394 gang_monitor->wait(Mutex::_no_safepoint_check_flag);
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395 }
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396 }
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