gem5  v20.1.0.0
Classes | Public Member Functions | Private Member Functions | Private Attributes | List of all members
EventQueue Class Reference

Queue of events sorted in time order. More...

#include <eventq.hh>


class  ScopedMigration
class  ScopedRelease

Public Member Functions

 EventQueue (const std::string &n)
void schedule (Event *event, Tick when, bool global=false)
 Schedule the given event on this queue. More...
void deschedule (Event *event)
 Deschedule the specified event. More...
void reschedule (Event *event, Tick when, bool always=false)
 Reschedule the specified event. More...
Tick nextTick () const
void setCurTick (Tick newVal)
Tick getCurTick () const
 While curTick() is useful for any object assigned to this event queue, if an object that is assigned to another event queue (or a non-event object) need to access the current tick of this event queue, this function is used. More...
EventgetHead () const
EventserviceOne ()
void serviceEvents (Tick when)
 process all events up to the given timestamp. More...
bool empty () const
 Returns true if no events are queued. More...
void dump () const
 This is a debugging function which will print everything on the event queue. More...
bool debugVerify () const
void handleAsyncInsertions ()
 Function for moving events from the async_queue to the main queue. More...
virtual void wakeup (Tick when=(Tick) -1)
 Function to signal that the event loop should be woken up because an event has been scheduled by an agent outside the gem5 event loop(s) whose event insertion may not have been noticed by gem5. More...
EventreplaceHead (Event *s)
 function for replacing the head of the event queue, so that a different set of events can run without disturbing events that have already been scheduled. More...
void checkpointReschedule (Event *event)
 Reschedule an event after a checkpoint. More...
virtual ~EventQueue ()
virtual const std::string name () const
void name (const std::string &st)
void lock ()
 Provide an interface for locking/unlocking the event queue. More...
void unlock ()

Private Member Functions

void insert (Event *event)
 Insert / remove event from the queue. More...
void remove (Event *event)
void asyncInsert (Event *event)
 Function for adding events to the async queue. More...
 EventQueue (const EventQueue &)

Private Attributes

std::string objName
Tick _curTick
std::mutex async_queue_mutex
 Mutex to protect async queue. More...
std::list< Event * > async_queue
 List of events added by other threads to this event queue. More...
std::mutex service_mutex
 Lock protecting event handling. More...

Detailed Description

Queue of events sorted in time order.

Events are scheduled (inserted into the event queue) using the schedule() method. This method either inserts a synchronous or asynchronous event.

Synchronous events are scheduled using schedule() method with the argument 'global' set to false (default). This should only be done from a thread holding the event queue lock (EventQueue::service_mutex). The lock is always held when an event handler is called, it can therefore always insert events into its own event queue unless it voluntarily releases the lock.

Events can be scheduled across thread (and event queue borders) by either scheduling asynchronous events or taking the target event queue's lock. However, the lock should never be taken directly since this is likely to cause deadlocks. Instead, code that needs to schedule events in other event queues should temporarily release its own queue and lock the new queue. This prevents deadlocks since a single thread never owns more than one event queue lock. This functionality is provided by the ScopedMigration helper class. Note that temporarily migrating between event queues can make the simulation non-deterministic, it should therefore be limited to cases where that can be tolerated (e.g., handling asynchronous IO or fast-forwarding in KVM).

Asynchronous events can also be scheduled using the normal schedule() method with the 'global' parameter set to true. Unlike the previous queue migration strategy, this strategy is fully deterministic. This causes the event to be inserted in a separate queue of asynchronous events (async_queue), which is merged main event queue at the end of each simulation quantum (by calling the handleAsyncInsertions() method). Note that this implies that such events must happen at least one simulation quantum into the future, otherwise they risk being scheduled in the past by handleAsyncInsertions().

Definition at line 617 of file eventq.hh.

Constructor & Destructor Documentation

◆ EventQueue()

EventQueue::EventQueue ( const EventQueue )

◆ ~EventQueue()

virtual EventQueue::~EventQueue ( )

Definition at line 964 of file eventq.hh.

References deschedule(), empty(), and getHead().

Member Function Documentation

◆ asyncInsert()

void EventQueue::asyncInsert ( Event event)

Function for adding events to the async queue.

The added events are added to main event queue later. Threads, other than the owning thread, should call this function instead of insert().

Definition at line 427 of file

References async_queue, async_queue_mutex, and MipsISA::event.

Referenced by schedule().

◆ checkpointReschedule()

void EventQueue::checkpointReschedule ( Event event)

Reschedule an event after a checkpoint.

Since events don't know which event queue they belong to, parent objects need to reschedule events themselves. This method conditionally schedules an event that has the Scheduled flag set. It should be called by parent objects after unserializing an object.

@warn Only use this method after unserializing an Event.

Definition at line 279 of file

References MipsISA::event, and EventBase::Scheduled.

◆ debugVerify()

bool EventQueue::debugVerify ( ) const

◆ getHead()

Event* EventQueue::getHead ( ) const

Definition at line 851 of file eventq.hh.

References head.

Referenced by RubySystem::memWriteback(), and ~EventQueue().

◆ handleAsyncInsertions()

void EventQueue::handleAsyncInsertions ( )

Function for moving events from the async_queue to the main queue.

Definition at line 435 of file

References async_queue, async_queue_mutex, curEventQueue(), and insert().

Referenced by doSimLoop(), and GlobalSyncEvent::BarrierEvent::process().

◆ insert()

void EventQueue::insert ( Event event)

Insert / remove event from the queue.

Should only be called by thread operating this queue.

Definition at line 111 of file

References MipsISA::event, Event::insertBefore(), and Event::nextBin.

Referenced by handleAsyncInsertions(), reschedule(), and schedule().

◆ lock()

void EventQueue::lock ( )

Provide an interface for locking/unlocking the event queue.

@warn Do NOT use these methods directly unless you really know what you are doing. Incorrect use can easily lead to simulator deadlocks.

See also

Definition at line 947 of file eventq.hh.

References service_mutex.

Referenced by DistIface::RecvScheduler::pushPacket(), DistIface::recvThreadFunc(), EventQueue::ScopedMigration::ScopedMigration(), EventQueue::ScopedMigration::~ScopedMigration(), and EventQueue::ScopedRelease::~ScopedRelease().

◆ nextTick()

Tick EventQueue::nextTick ( ) const

◆ remove()

void EventQueue::remove ( Event event)

Definition at line 165 of file

References MipsISA::event, Event::nextBin, panic, and Event::removeItem().

Referenced by deschedule(), and reschedule().

◆ replaceHead()

Event * EventQueue::replaceHead ( Event s)

function for replacing the head of the event queue, so that a different set of events can run without disturbing events that have already been scheduled.

Already scheduled events can be processed by replacing the original head back. USING THIS FUNCTION CAN BE DANGEROUS TO THE HEALTH OF THE SIMULATOR. NOT RECOMMENDED FOR USE.

Definition at line 355 of file

References ArmISA::s, and ArmISA::t.

Referenced by RubySystem::startup().

◆ serviceOne()

Event * EventQueue::serviceOne ( )

◆ setCurTick()

void EventQueue::setCurTick ( Tick  newVal)

Definition at line 837 of file eventq.hh.

References _curTick.

Referenced by StatTest::run(), serviceEvents(), and EventManager::setCurTick().

◆ unlock()

void EventQueue::unlock ( )

Member Data Documentation

◆ _curTick

Tick EventQueue::_curTick

Definition at line 622 of file eventq.hh.

Referenced by getCurTick(), and setCurTick().

◆ async_queue

std::list<Event*> EventQueue::async_queue

List of events added by other threads to this event queue.

Definition at line 628 of file eventq.hh.

Referenced by asyncInsert(), and handleAsyncInsertions().

◆ async_queue_mutex

std::mutex EventQueue::async_queue_mutex

Mutex to protect async queue.

Definition at line 625 of file eventq.hh.

Referenced by asyncInsert(), and handleAsyncInsertions().

◆ head

Event* EventQueue::head

Definition at line 621 of file eventq.hh.

Referenced by empty(), getHead(), and nextTick().

◆ objName

std::string EventQueue::objName

Definition at line 620 of file eventq.hh.

Referenced by name().

◆ service_mutex

std::mutex EventQueue::service_mutex

Lock protecting event handling.

This lock is always taken when servicing events. It is assumed that the thread scheduling new events (not asynchronous events though) have taken this lock. This is normally done by serviceOne() since new events are typically scheduled as a response to an earlier event.

This lock is intended to be used to temporarily steal an event queue to support inter-thread communication when some deterministic timing can be sacrificed for speed. For example, the KVM CPU can use this support to access devices running in a different thread.

See also

Definition at line 650 of file eventq.hh.

Referenced by lock(), and unlock().

The documentation for this class was generated from the following files:

Generated on Wed Sep 30 2020 14:02:24 for gem5 by doxygen 1.8.17