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dfs.cpp
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1 /* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
2 /*
3  * Main authors:
4  * Christian Schulte <schulte@gecode.org>
5  *
6  * Copyright:
7  * Christian Schulte, 2009
8  *
9  * Last modified:
10  * $Date: 2015-01-08 15:07:24 +0100 (Thu, 08 Jan 2015) $ by $Author: schulte $
11  * $Revision: 14341 $
12  *
13  * This file is part of Gecode, the generic constraint
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15  * http://www.gecode.org
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37 
38 #include <gecode/support.hh>
39 
40 #ifdef GECODE_HAS_THREADS
41 
43 
44 namespace Gecode { namespace Search { namespace Parallel {
45 
46  /*
47  * Statistics
48  */
49  Statistics
50  DFS::statistics(void) const {
51  Statistics s;
52  for (unsigned int i=0; i<workers(); i++)
53  s += worker(i)->statistics();
54  return s;
55  }
56 
57 
58  /*
59  * Engine: search control
60  */
61  void
63  /*
64  * The engine maintains the following invariant:
65  * - If the current space (cur) is not NULL, the path always points
66  * to exactly that space.
67  * - If the current space (cur) is NULL, the path always points
68  * to the next space (if there is any).
69  *
70  * This invariant is needed so that no-goods can be extracted properly
71  * when the engine is stopped or has found a solution.
72  *
73  */
74  // Peform initial delay, if not first worker
75  if (this != engine().worker(0))
77  // Okay, we are in business, start working
78  while (true) {
79  switch (engine().cmd()) {
80  case C_WAIT:
81  // Wait
82  engine().wait();
83  break;
84  case C_TERMINATE:
85  // Acknowledge termination request
87  // Wait until termination can proceed
89  // Terminate thread
90  engine().terminated();
91  return;
92  case C_RESET:
93  // Acknowledge reset request
95  // Wait until reset has been performed
96  engine().wait_reset();
97  // Acknowledge that reset cycle is over
99  break;
100  case C_WORK:
101  // Perform exploration work
102  {
103  m.acquire();
104  if (idle) {
105  m.release();
106  // Try to find new work
107  find();
108  } else if (cur != NULL) {
109  start();
110  if (stop(engine().opt())) {
111  // Report stop
112  m.release();
113  engine().stop();
114  } else {
115  node++;
116  switch (cur->status(*this)) {
117  case SS_FAILED:
118  fail++;
119  delete cur;
120  cur = NULL;
121  path.next();
122  m.release();
123  break;
124  case SS_SOLVED:
125  {
126  // Deletes all pending branchers
127  (void) cur->choice();
128  Space* s = cur->clone(false);
129  delete cur;
130  cur = NULL;
131  path.next();
132  m.release();
133  engine().solution(s);
134  }
135  break;
136  case SS_BRANCH:
137  {
138  Space* c;
139  if ((d == 0) || (d >= engine().opt().c_d)) {
140  c = cur->clone();
141  d = 1;
142  } else {
143  c = NULL;
144  d++;
145  }
146  const Choice* ch = path.push(*this,cur,c);
147  cur->commit(*ch,0);
148  m.release();
149  }
150  break;
151  default:
152  GECODE_NEVER;
153  }
154  }
155  } else if (!path.empty()) {
156  cur = path.recompute(d,engine().opt().a_d,*this);
157  if (cur == NULL)
158  path.next();
159  m.release();
160  } else {
161  idle = true;
162  path.ngdl(0);
163  m.release();
164  // Report that worker is idle
165  engine().idle();
166  }
167  }
168  break;
169  default:
170  GECODE_NEVER;
171  }
172  }
173  }
174 
175 
176  /*
177  * Perform reset
178  *
179  */
180  void
182  // Grab wait lock for reset
184  // Release workers for reset
185  release(C_RESET);
186  // Wait for reset cycle started
188  // All workers are marked as busy again
189  n_busy = workers();
190  for (unsigned int i=1U; i<workers(); i++)
191  worker(i)->reset(NULL,0);
192  worker(0U)->reset(s,opt().nogoods_limit);
193  // Block workers again to ensure invariant
194  block();
195  // Release reset lock
197  // Wait for reset cycle stopped
199  }
200 
201 
202 
203  /*
204  * Create no-goods
205  *
206  */
207  NoGoods&
208  DFS::nogoods(void) {
209  NoGoods* ng;
210  // Grab wait lock for reset
212  // Release workers for reset
213  release(C_RESET);
214  // Wait for reset cycle started
216  ng = &worker(0)->nogoods();
217  // Block workers again to ensure invariant
218  block();
219  // Release reset lock
221  // Wait for reset cycle stopped
223  return *ng;
224  }
225 
226 
227  /*
228  * Termination and deletion
229  */
230  DFS::~DFS(void) {
231  terminate();
232  heap.rfree(_worker);
233  }
234 
235 }}}
236 
237 #endif
238 
239 // STATISTICS: search-parallel
Support::Event e_reset_ack_start
Event for reset acknowledgment started.
Definition: engine.hh:147
Space must be branched (at least one brancher left)
Definition: core.hpp:1303
void ack_terminate(void)
For worker to acknowledge termination command.
Definition: engine.hh:335
void wait_terminate(void)
For worker to wait until termination is legal.
Definition: engine.hh:343
void wait_reset(void)
For worker to wait for all workers to reset.
Definition: engine.hh:385
void terminate(void)
For engine to peform thread termination.
Definition: engine.hh:349
Path path
Current path ins search tree.
Definition: engine.hh:59
Search engine statistics
Definition: search.hh:136
void rfree(void *p)
Free memory block starting at p.
Definition: heap.hpp:355
Space * clone(bool share=true, CloneStatistics &stat=unused_clone) const
Clone space.
Definition: core.hpp:2854
void idle(void)
Report that worker is idle.
Definition: engine.hh:293
Statistics statistics(void)
Return statistics.
Definition: engine.hh:277
const unsigned int initial_delay
Initial delay in milliseconds for all but first worker thread.
Definition: search.hh:104
Worker * worker(unsigned int i) const
Provide access to worker i.
Definition: dfs.hh:98
void acquire(void)
Acquire the mutex and possibly block.
Definition: none.hpp:46
unsigned long int fail
Number of failed nodes in search tree.
Definition: search.hh:139
Perform reset operation.
Definition: engine.hh:94
void stop(void)
Report that worker has been stopped.
Definition: engine.hh:309
virtual void run(void)
Start execution of worker.
Definition: dfs.cpp:62
void block(void)
Block all workers.
Definition: engine.hh:222
Computation spaces.
Definition: core.hpp:1362
void find(void)
Try to find some work.
Definition: dfs.hh:165
volatile unsigned int n_busy
Number of busy workers.
Definition: engine.hh:171
Heap heap
The single global heap.
Definition: heap.cpp:49
void start(void)
Reset stop information.
Definition: worker.hh:78
void release(void)
Release the mutex.
Definition: none.hpp:52
Gecode::FloatVal c(-8, 8)
bool empty(void) const
Test whether path is empty.
Definition: path.hh:273
virtual NoGoods & nogoods(void)
Return no-goods.
Definition: dfs.cpp:208
void wait(void)
Ensure that worker waits.
Definition: engine.hh:232
Gecode::IntArgs i(4, 1, 2, 3, 4)
Support::Mutex m_wait_reset
Mutex for waiting for reset.
Definition: engine.hh:151
unsigned int d
Distance until next clone.
Definition: engine.hh:63
void reset(Space *s, int ngdl)
Reset worker to restart at space s.
Definition: dfs.hh:131
bool idle
Whether the worker is idle.
Definition: engine.hh:65
const unsigned int a_d
Create a clone during recomputation if distance is greater than a_d (adaptive distance) ...
Definition: search.hh:99
Cmd cmd(void) const
Return current command.
Definition: engine.hh:218
const Choice * push(Worker &stat, Space *s, Space *c)
Push space c (a clone of s or NULL)
Definition: path.hh:239
void commit(const Choice &c, unsigned int a, CommitStatistics &stat=unused_commit)
Commit choice c for alternative a.
Definition: core.hpp:2862
static void sleep(unsigned int ms)
Put current thread to sleep for ms milliseconds.
Definition: none.hpp:78
virtual void reset(Space *s)
Reset engine to restart at space s.
Definition: dfs.cpp:181
void terminated(void)
For worker to register termination.
Definition: engine.hh:323
Space * cur
Current space being explored.
Definition: engine.hh:61
unsigned int workers(void) const
Return number of workers.
Definition: engine.hh:209
const Options & opt(void) const
Provide access to search options.
Definition: engine.hh:205
Space * recompute(unsigned int &d, unsigned int a_d, Worker &s)
Recompute space according to path.
Definition: path.hh:353
virtual Statistics statistics(void) const
Return statistics.
Definition: dfs.cpp:50
void next(void)
Generate path for next node.
Definition: path.hh:253
int ngdl(void) const
Return no-good depth limit.
Definition: path.hh:229
void ack_reset_stop(void)
For worker to acknowledge stop of reset cycle.
Definition: engine.hh:377
void solution(Space *s)
Report solution s.
Definition: dfs.hh:150
Choice for performing commit
Definition: core.hpp:1036
No-goods recorded from restarts.
Definition: core.hpp:1240
void release(Cmd c)
Release all workers.
Definition: engine.hh:227
SpaceStatus status(StatusStatistics &stat=unused_status)
Query space status.
Definition: core.cpp:252
const unsigned int c_d
Create a clone after every c_d commits (commit distance)
Definition: search.hh:97
Gecode toplevel namespace
DFS & engine(void) const
Provide access to engine.
Definition: dfs.hh:94
unsigned long int node
Number of nodes expanded.
Definition: search.hh:141
const unsigned int nogoods_limit
Depth limit for no-good generation during search.
Definition: search.hh:107
Worker ** _worker
Array of worker references.
Definition: dfs.hh:63
Space is failed
Definition: core.hpp:1301
const Choice * choice(void)
Create new choice for current brancher.
Definition: core.cpp:366
NoGoods & nogoods(void)
Return no-goods.
Definition: engine.hh:418
void ack_reset_start(void)
For worker to acknowledge start of reset cycle.
Definition: engine.hh:369
#define GECODE_NEVER
Assert that this command is never executed.
Definition: macros.hpp:60
void wait(void)
Wait until the event becomes signalled.
Definition: none.hpp:65
bool stop(const Options &o)
Check whether engine must be stopped.
Definition: worker.hh:83
Support::Event e_reset_ack_stop
Event for reset acknowledgment stopped.
Definition: engine.hh:149
Support::Mutex m
Mutex for access to worker.
Definition: engine.hh:57
virtual ~DFS(void)
Destructor.
Definition: dfs.cpp:230
Space is solved (no brancher left)
Definition: core.hpp:1302