Scheduler::PhysicalTaskPtr
Scheduler::take_runnable_task(const Locality &locality){
const auto tid = locality.self_thread_id();
PhysicalTaskPtr task;
// try to take an unstealable task
task = take_unstealable_task(locality);
if(task){ return task; }
// try to take a local stealable task
task = take_local_stealable_task(locality);
if(task){ return task; }
// try to steal an task
task = steal_task(locality);
if(task){ return task; }
// attempt to sleep
auto &sync = m_synchronizers[tid];
while(true){
sync.set_is_sleeping();
if(task || is_finished() || is_cancelled()){ break; }
// try to take an unstealable task
task = take_unstealable_task(locality);
if(task){ break; }
// try to steal an task
task = steal_task(locality);
if(task){ break; }
// wait for new task
sync.wait();
}
sync.reset_is_sleeping();
return task;
}
void run_core(std::size_t core_id)
{
task_pack<TASK> tmp_task;
while(cores_[core_id].running)
{
if(cores_[core_id].queue_size() > 0)
{ // Still has unfinished tasks.
cores_[core_id].execute(this);
}
else if(can_steal())
{ // Steal from other cores (at random).
try
{
tmp_task = steal_task();
}
catch(...)
{
// The queue got emptied before steal_task() could
// finnish.
cores_[core_id].running = false;
break;
}
cores_[core_id].add_task(std::move(tmp_task));
cores_[core_id].execute(this);
}
else
{ // No task in the entire schedulet that could be run
// by this core.
cores_[core_id].running = false;
}
}
}
/** Steal work from another worker's task stack */
static int steal(struct generic_task_desc * _tweed_top_,
struct worker_desc * victim) {
struct generic_task_desc * stolenTask;
struct worker_desc * me = (struct worker_desc *) thread_get_tls();
LOCK(victim->lock);
stolenTask = victim->bot;
// check if there is actually work to steal
if (stolenTask != NULL && stolenTask->balarm == TWEED_TASK_NEW) {
// try to steal task
tweed_task_func_t func = steal_task(stolenTask, me);
if (func == NULL) {
// we didn't succeed in the steal, back off
#ifndef TWEED_USE_CAS
stolenTask->balarm = TWEED_TASK_INLINED;
stolenTask->thief = NULL;
#endif
UNLOCK(victim->lock);
return 0; // didn't steal anything
} else {
// we have stolen the task, update bot
atomic_inc(&(victim->bot), stolenTask->size);
UNLOCK(victim->lock);
// and run task
trace_event(TRACE_SUBSYS_TWEED, TRACE_EVENT_TWEED_STEAL, victim->core_id);
func(_tweed_top_, stolenTask);
trace_event(TRACE_SUBSYS_TWEED, TRACE_EVENT_TWEED_STEAL_END,
victim->core_id);
// signal task completion
stolenTask->balarm |= TWEED_TASK_COMPLETE;
return 1;
}
} else {
UNLOCK(victim->lock);
return 0; // didn't steal anything
}
}
