/// Thread::idle_loop() is where the thread is parked when it has no work to do.
/// The parameter 'master_sp', if non-NULL, is a pointer to an active SplitPoint
/// object for which the thread is the master.
internal void idle_loop(SplitPoint sp_master, ManualResetEvent initEvent)
{
if (initEvent != null)
{
// Signal done
initEvent.Set();
}
bool use_sleeping_threads = Threads.useSleepingThreads;
// If this thread is the master of a split point and all slaves have
// finished their work at this split point, return from the idle loop.
while ((sp_master == null) || (sp_master.slavesMask != 0))
{
// If we are not searching, wait for a condition to be signaled
// instead of wasting CPU time polling for work.
while (do_sleep ||
do_exit ||
(!is_searching && use_sleeping_threads))
{
if (do_exit)
{
Debug.Assert(sp_master == null);
return;
}
// Grab the lock to avoid races with Thread::wake_up()
ThreadHelper.lock_grab(sleepLock);
// If we are master and all slaves have finished don't go to sleep
if ((sp_master != null) && (sp_master.slavesMask == 0))
{
ThreadHelper.lock_release(sleepLock);
break;
}
// Do sleep after retesting sleep conditions under lock protection, in
// particular we need to avoid a deadlock in case a master thread has,
// in the meanwhile, allocated us and sent the wake_up() call before we
// had the chance to grab the lock.
if (do_sleep || !is_searching)
{
ThreadHelper.cond_wait(sleepCond, sleepLock);
}
ThreadHelper.lock_release(sleepLock);
}
// If this thread has been assigned work, launch a search
if (is_searching)
{
Debug.Assert(!do_sleep && !do_exit);
ThreadHelper.lock_grab(Threads.splitLock);
Debug.Assert(is_searching);
SplitPoint sp = curSplitPoint;
ThreadHelper.lock_release(Threads.splitLock);
LoopStack ls = LoopStackBroker.GetObject();
Stack[] ss = ls.ss;
int ssPos = 0;
Position pos = PositionBroker.GetObject();
pos.copy(sp.pos, this);
Array.Copy(sp.ss, sp.ssPos - 1, ss, ssPos, 4);
ss[ssPos + 1].sp = sp;
ThreadHelper.lock_grab(sp.Lock);
if (sp.nodeType == NodeTypeC.Root)
{
Search.search(NodeTypeC.SplitPointRoot, pos, ss, ssPos + 1, sp.alpha, sp.beta, sp.depth);
}
else if (sp.nodeType == NodeTypeC.PV)
{
Search.search(NodeTypeC.SplitPointPV, pos, ss, ssPos + 1, sp.alpha, sp.beta, sp.depth);
}
else if (sp.nodeType == NodeTypeC.NonPV)
{
Search.search(NodeTypeC.SplitPointNonPV, pos, ss, ssPos + 1, sp.alpha, sp.beta, sp.depth);
}
else
{
Debug.Assert(false);
}
Debug.Assert(is_searching);
is_searching = false;
#if ACTIVE_REPARENT
sp.allSlavesRunning = false;
#endif
sp.slavesMask &= ~(1UL << idx);
sp.nodes += pos.nodes;
// Wake up master thread so to allow it to return from the idle loop in
// case we are the last slave of the split point.
if (use_sleeping_threads &&
this != sp.master &&
!sp.master.is_searching)
{
sp.master.wake_up();
}
// After releasing the lock we cannot access anymore any SplitPoint
// related data in a safe way becuase it could have been released under
// our feet by the sp master. Also accessing other Thread objects is
// unsafe because if we are exiting there is a chance are already freed.
ThreadHelper.lock_release(sp.Lock);
#if ACTIVE_REPARENT
// Try to reparent to the first split point, with still all slaves
// running, where we are available as a possible slave.
for (int i = 0; i < Threads.size(); i++)
{
Thread th = Threads.threads[i];
int spCnt = th.splitPointsCnt;
SplitPoint latest = th.splitPoints[spCnt != 0 ? spCnt - 1 : 0];
if (this.is_available_to(th) &&
spCnt > 0 &&
!th.cutoff_occurred() &&
latest.allSlavesRunning &&
Utils.more_than_one(latest.slavesMask))
{
ThreadHelper.lock_grab(latest.Lock);
ThreadHelper.lock_grab(Threads.splitLock);
// Retest all under lock protection, we are in the middle
// of a race storm here !
if (this.is_available_to(th) &&
spCnt == th.splitPointsCnt &&
!th.cutoff_occurred() &&
latest.allSlavesRunning &&
Utils.more_than_one(latest.slavesMask))
{
latest.slavesMask |= 1UL << idx;
curSplitPoint = latest;
is_searching = true;
}
ThreadHelper.lock_release(Threads.splitLock);
ThreadHelper.lock_release(latest.Lock);
break; // Exit anyhow, only one try (enough in 99% of cases)
}
}
#endif
pos.startState = null;
pos.st = null;
PositionBroker.Free();
LoopStackBroker.Free(ls);
}
}
}
// split() does the actual work of distributing the work at a node between
// several available threads. If it does not succeed in splitting the node
// (because no idle threads are available, or because we have no unused split
// point objects), the function immediately returns. If splitting is possible, a
// SplitPoint object is initialized with all the data that must be copied to the
// helper threads and then helper threads are told that they have been assigned
// work. This will cause them to instantly leave their idle loops and call
// search(). When all threads have returned from search() then split() returns.
internal static Value split(bool Fake, Position pos, Stack[] ss, int ssPos, Value alpha, Value beta,
Value bestValue, ref Move bestMove, Depth depth, Move threatMove,
int moveCount, MovePicker mp, int nodeType)
{
Debug.Assert(pos.pos_is_ok());
Debug.Assert(bestValue > -ValueC.VALUE_INFINITE);
Debug.Assert(bestValue <= alpha);
Debug.Assert(alpha < beta);
Debug.Assert(beta <= ValueC.VALUE_INFINITE);
Debug.Assert(depth > DepthC.DEPTH_ZERO);
Thread master = pos.this_thread();
if (master.splitPointsCnt >= Constants.MAX_SPLITPOINTS_PER_THREAD)
{
return(bestValue);
}
// Pick the next available split point from the split point stack
SplitPoint sp = master.splitPoints[master.splitPointsCnt];
sp.parent = master.curSplitPoint;
sp.master = master;
sp.cutoff = false;
sp.slavesMask = 1UL << master.idx;
#if ACTIVE_REPARENT
sp.allSlavesRunning = true;
#endif
sp.depth = depth;
sp.bestMove = bestMove;
sp.threatMove = threatMove;
sp.alpha = alpha;
sp.beta = beta;
sp.nodeType = nodeType;
sp.bestValue = bestValue;
sp.mp = mp;
sp.moveCount = moveCount;
sp.pos = pos;
sp.nodes = 0;
sp.ss = ss;
sp.ssPos = ssPos;
Debug.Assert(master.is_searching);
master.curSplitPoint = sp;
int slavesCnt = 0;
ThreadHelper.lock_grab(sp.Lock);
ThreadHelper.lock_grab(splitLock);
for (int i = 0; i < size() && !Fake; ++i)
{
if (threads[i].is_available_to(master))
{
sp.slavesMask |= 1UL << i;
threads[i].curSplitPoint = sp;
threads[i].is_searching = true; // Slave leaves idle_loop()
if (useSleepingThreads)
{
threads[i].wake_up();
}
if (++slavesCnt + 1 >= maxThreadsPerSplitPoint) // Master is always included
{
break;
}
}
}
master.splitPointsCnt++;
ThreadHelper.lock_release(splitLock);
ThreadHelper.lock_release(sp.Lock);
// Everything is set up. The master thread enters the idle loop, from which
// it will instantly launch a search, because its is_searching flag is set.
// We pass the split point as a parameter to the idle loop, which means that
// the thread will return from the idle loop when all slaves have finished
// their work at this split point.
if (slavesCnt != 0 || Fake)
{
master.idle_loop(sp, null);
// In helpful master concept a master can help only a sub-tree of its split
// point, and because here is all finished is not possible master is booked.
Debug.Assert(!master.is_searching);
}
// We have returned from the idle loop, which means that all threads are
// finished. Note that setting is_searching and decreasing activeSplitPoints is
// done under lock protection to avoid a race with Thread::is_available_to().
ThreadHelper.lock_grab(sp.Lock); // To protect sp->nodes
ThreadHelper.lock_grab(splitLock);
master.is_searching = true;
master.splitPointsCnt--;
master.curSplitPoint = sp.parent;
pos.nodes += sp.nodes;
bestMove = sp.bestMove;
ThreadHelper.lock_release(splitLock);
ThreadHelper.lock_release(sp.Lock);
return(sp.bestValue);
}
internal void wake_up()
{
ThreadHelper.lock_grab(sleepLock);
ThreadHelper.cond_signal(sleepCond);
ThreadHelper.lock_release(sleepLock);
}
