#include <WaitingTaskList.h>

Classes
struct	WaitNode

Public Member Functions
void	add (WaitingTask *)
	Adds task to the waiting list. More...

void	doneWaiting (std::exception_ptr iPtr)
	Signals that the resource is now available and tasks should be spawned. More...

void	reset ()
	Resets access to the resource so that added tasks will wait. More...

	WaitingTaskList (unsigned int iInitialSize=2)
	Constructor. More...

	~WaitingTaskList ()=default

Private Member Functions
void	announce ()

WaitNode *	createNode (WaitingTask *iTask)

const WaitingTaskList &	operator= (const WaitingTaskList &)=delete

	WaitingTaskList (const WaitingTaskList &)=delete

Private Attributes
std::exception_ptr	m_exceptionPtr

std::atomic< WaitNode * >	m_head

std::atomic< unsigned int >	m_lastAssignedCacheIndex

std::unique_ptr< WaitNode[]>	m_nodeCache

unsigned int	m_nodeCacheSize

std::atomic< bool >	m_waiting

Detailed Description

Definition at line 102 of file WaitingTaskList.h.

Constructor & Destructor Documentation

WaitingTaskList::WaitingTaskList ( unsigned int iInitialSize = 2 )

explicit

Constructor.

The WaitingTaskList is initial set to waiting.

Parameters

[in] iInitialSize specifies the initial size of the cache used to hold waiting tasks. The value is only useful for optimization as the object can resize itself.

Definition at line 36 of file WaitingTaskList.cc.

References m_lastAssignedCacheIndex, m_nodeCache, m_nodeCacheSize, and m_waiting.

                                                          :
 m_head{nullptr},
 m_nodeCache{new WaitNode[iInitialSize]},
 m_nodeCacheSize{iInitialSize},
 m_lastAssignedCacheIndex{0},
 m_waiting{true}
 {
   auto nodeCache = m_nodeCache.get();
   for(auto it = nodeCache, itEnd = nodeCache+m_nodeCacheSize; it!=itEnd; ++it) {
     it->m_fromCache=true;
   }
 }

edm::WaitingTaskList::~WaitingTaskList ( )

default

edm::WaitingTaskList::WaitingTaskList ( const WaitingTaskList & )

privatedelete

Member Function Documentation

void WaitingTaskList::add ( WaitingTask * iTask )

Adds task to the waiting list.

If doneWaiting() has already been called then the added task will immediately be spawned. If that is not the case then the task will be held until doneWaiting() is called and will then be spawned. Calls to add() and doneWaiting() can safely be done concurrently.

Definition at line 96 of file WaitingTaskList.cc.

References announce(), createNode(), edm::WaitingTask::dependentTaskFailed(), m_exceptionPtr, m_head, m_waiting, edm::WaitingTaskList::WaitNode::setNextNode(), and unlikely.

Referenced by edm::NoProcessProductResolver::prefetchAsync_(), edm::Path::processOneOccurrenceAsync(), counter.Counter::register(), SequenceTypes.Task::remove(), and SequenceTypes.Task::replace().

                                        {
   iTask->increment_ref_count();
   if(!m_waiting) {
     if(unlikely(bool(m_exceptionPtr))) {
       iTask->dependentTaskFailed(m_exceptionPtr);
     }
     if(0==iTask->decrement_ref_count()) {
       tbb::task::spawn(*iTask);
     }
   } else {
     WaitNode* newHead = createNode(iTask);
     //This exchange is sequentially consistent thereby
     // ensuring ordering between it and setNextNode
     WaitNode* oldHead = m_head.exchange(newHead);
     newHead->setNextNode(oldHead);
 
     //For the case where oldHead != nullptr,
     // even if 'm_waiting' changed, we don't
     // have to recheck since we beat 'announce()' in
     // the ordering of 'm_head.exchange' call so iTask
     // is guaranteed to be in the link list
 
     if(nullptr == oldHead) {
       if(!m_waiting) {
         //if finished waiting right before we did the
         // exchange our task will not be spawned. Also,
         // additional threads may be calling add() and swapping
         // heads and linking us to the new head.
         // It is safe to call announce from multiple threads
         announce();
       }
     }
   }
 }

void WaitingTaskList::announce ( )

private

Handles spawning the tasks, safe to call from multiple threads

Definition at line 132 of file WaitingTaskList.cc.

References m_exceptionPtr, edm::WaitingTaskList::WaitNode::m_fromCache, m_head, edm::WaitingTaskList::WaitNode::m_task, gen::n, GetRecoTauVFromDQM_MC_cff::next, edm::WaitingTaskList::WaitNode::nextNode(), lumiQTWidget::t, and unlikely.

Referenced by add(), and doneWaiting().

 {
   //Need a temporary storage since one of these tasks could
   // cause the next event to start processing which would refill
   // this waiting list after it has been reset
   WaitNode* n = m_head.exchange(nullptr);
   WaitNode* next;
   while(n) {
     //it is possible that 'WaitingTaskList::add' is running in a different
     // thread and we have a new 'head' but the old head has not yet been
     // attached to the new head (we identify this since 'nextNode' will return itself).
     //  In that case we have to wait until the link has been established before going on.
     while(n == (next=n->nextNode())) {
       hardware_pause();
     }
     auto t = n->m_task;
     if(unlikely(bool(m_exceptionPtr))) {
       t->dependentTaskFailed(m_exceptionPtr);
     }
     if(0==t->decrement_ref_count()){
       tbb::task::spawn(*t);
     }
     if(!n->m_fromCache ) {
       delete n;
     }
     n=next;
   }
 }

WaitingTaskList::WaitNode * WaitingTaskList::createNode ( WaitingTask * iTask )

private

Definition at line 74 of file WaitingTaskList.cc.

References edm::WaitingTaskList::WaitNode::m_fromCache, m_lastAssignedCacheIndex, edm::WaitingTaskList::WaitNode::m_next, m_nodeCache, m_nodeCacheSize, and edm::WaitingTaskList::WaitNode::m_task.

Referenced by add().

 {
   unsigned int index = m_lastAssignedCacheIndex++;
   
   WaitNode* returnValue;
   if( index < m_nodeCacheSize) {
     returnValue = m_nodeCache.get()+index;
   } else {
     returnValue = new WaitNode;
     returnValue->m_fromCache=false;
   }
   returnValue->m_task = iTask;
   //No other thread can see m_next yet. The caller to create node
   // will be doing a synchronization operation anyway which will
   // make sure m_task and m_next are synched across threads
   returnValue->m_next.store(returnValue,std::memory_order_relaxed);
   
   return returnValue;
 }

void WaitingTaskList::doneWaiting ( std::exception_ptr iPtr )

Signals that the resource is now available and tasks should be spawned.

The owner of the resource calls this function to allow the waiting tasks to start accessing it. If the task fails, a non 'null' std::exception_ptr should be used. To have tasks wait again one must call reset(). Calls to add() and doneWaiting() can safely be done concurrently.

Definition at line 162 of file WaitingTaskList.cc.

References announce(), m_exceptionPtr, and m_waiting.

Referenced by edm::Path::finished(), edm::Worker::prePrefetchSelectionAsync(), edm::NoProcessProductResolver::setCache(), and edm::Worker::skipOnPath().

 {
   m_exceptionPtr = iPtr;
   m_waiting=false;
   announce();
 }

const WaitingTaskList& edm::WaitingTaskList::operator= ( const WaitingTaskList & )

privatedelete

void WaitingTaskList::reset ( void )

Resets access to the resource so that added tasks will wait.

The owner of the resouce calls reset() to make tasks wait. Calling reset() is NOT thread safe. The system must guarantee that no tasks are using the resource when reset() is called and neither add() nor doneWaiting() can be called concurrently with reset().

Definition at line 53 of file WaitingTaskList.cc.

References m_exceptionPtr, m_head, m_lastAssignedCacheIndex, m_nodeCache, m_nodeCacheSize, and m_waiting.

Referenced by edm::Path::processOneOccurrenceAsync(), and edm::NoProcessProductResolver::resetProductData_().

 {
   m_exceptionPtr = std::exception_ptr{};
   unsigned int nSeenTasks = m_lastAssignedCacheIndex;
   m_lastAssignedCacheIndex = 0;
   assert(m_head == nullptr);
   if (nSeenTasks > m_nodeCacheSize) {
     //need to expand so next time we don't have to do any
     // memory requests
     m_nodeCacheSize = nSeenTasks;
     m_nodeCache.reset( new WaitNode[nSeenTasks] );
     auto nodeCache = m_nodeCache.get();
     for(auto it = nodeCache, itEnd = nodeCache+m_nodeCacheSize; it!=itEnd; ++it) {
       it->m_fromCache=true;
     }
   }
   //this will make sure all cores see the changes
   m_waiting = true;
 }