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unison/src/simulator/realtime-simulator-impl.cc

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/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
* Copyright (c) 2008 University of Washington
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation;
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "simulator.h"
#include "realtime-simulator-impl.h"
#include "wall-clock-synchronizer.h"
#include "scheduler.h"
#include "event-impl.h"
#include "synchronizer.h"
#include "ns3/ptr.h"
#include "ns3/pointer.h"
#include "ns3/assert.h"
#include "ns3/fatal-error.h"
#include "ns3/log.h"
#include "ns3/system-mutex.h"
#include "ns3/boolean.h"
#include "ns3/enum.h"
#include <math.h>
NS_LOG_COMPONENT_DEFINE ("RealtimeSimulatorImpl");
namespace ns3 {
NS_OBJECT_ENSURE_REGISTERED (RealtimeSimulatorImpl);
TypeId
RealtimeSimulatorImpl::GetTypeId (void)
{
static TypeId tid = TypeId ("ns3::RealtimeSimulatorImpl")
.SetParent<Object> ()
.AddConstructor<RealtimeSimulatorImpl> ()
.AddAttribute ("SynchronizationMode",
"What to do if the simulation cannot keep up with real time.",
EnumValue (SYNC_BEST_EFFORT),
MakeEnumAccessor (&RealtimeSimulatorImpl::SetSynchronizationMode),
MakeEnumChecker (SYNC_BEST_EFFORT, "BestEffort",
SYNC_HARD_LIMIT, "HardLimit"))
.AddAttribute ("HardLimit",
"Maximum acceptable real-time jitter (used in conjunction with SynchronizationMode=HardLimit)",
TimeValue (Seconds (0.1)),
MakeTimeAccessor (&RealtimeSimulatorImpl::m_hardLimit),
MakeTimeChecker ())
;
return tid;
}
RealtimeSimulatorImpl::RealtimeSimulatorImpl ()
{
NS_LOG_FUNCTION_NOARGS ();
m_stop = false;
m_running = false;
// uids are allocated from 4.
// uid 0 is "invalid" events
// uid 1 is "now" events
// uid 2 is "destroy" events
m_uid = 4;
// before ::Run is entered, the m_currentUid will be zero
m_currentUid = 0;
m_currentTs = 0;
m_unscheduledEvents = 0;
// Be very careful not to do anything that would cause a change or assignment
// of the underlying reference counts of m_synchronizer or you will be sorry.
m_synchronizer = CreateObject<WallClockSynchronizer> ();
}
RealtimeSimulatorImpl::~RealtimeSimulatorImpl ()
{
NS_LOG_FUNCTION_NOARGS ();
while (m_events->IsEmpty () == false)
{
Scheduler::Event next = m_events->RemoveNext ();
next.impl->Unref ();
}
m_events = 0;
m_synchronizer = 0;
}
void
RealtimeSimulatorImpl::Destroy ()
{
NS_LOG_FUNCTION_NOARGS ();
//
// This function is only called with the private version "disconnected" from
// the main simulator functions. We rely on the user not calling
// Simulator::Destroy while there is a chance that a worker thread could be
// accessing the current instance of the private object. In practice this
// means shutting down the workers and doing a Join() before calling the
// Simulator::Destroy().
//
while (m_destroyEvents.empty () == false)
{
Ptr<EventImpl> ev = m_destroyEvents.front ().PeekEventImpl ();
m_destroyEvents.pop_front ();
NS_LOG_LOGIC ("handle destroy " << ev);
if (ev->IsCancelled () == false)
{
ev->Invoke ();
}
}
}
void
RealtimeSimulatorImpl::SetScheduler (Ptr<Scheduler> scheduler)
{
NS_LOG_FUNCTION_NOARGS ();
{
CriticalSection cs (m_mutex);
if (m_events != 0)
{
while (m_events->IsEmpty () == false)
{
Scheduler::Event next = m_events->RemoveNext ();
scheduler->Insert (next);
}
}
m_events = scheduler;
}
}
Ptr<Scheduler>
RealtimeSimulatorImpl::GetScheduler (void) const
{
NS_LOG_FUNCTION_NOARGS ();
return m_events;
}
void
RealtimeSimulatorImpl::ProcessOneEvent (void)
{
NS_LOG_FUNCTION_NOARGS ();
//
// The idea here is to wait until the next event comes due. In the case of
// a realtime simulation, we want real time to be consumed between events.
// It is the realtime synchronizer that causes real time to be consumed by
// doing some kind of a wait.
//
// We need to be able to have external events (such as a packet reception event)
// cause us to re-evaluate our state. The way this works is that the synchronizer
// gets interrupted and returs. So, there is a possibility that things may change
// out from under us dynamically. In this case, we need to re-evaluate how long to
// wait in a for-loop until we have waited sucessfully (until a timeout) for the
// event at the head of the event list.
//
// m_synchronizer->Synchronize will return true if the wait was completed without
// interruption, otherwise it will return false indicating that something has changed
// out from under us. If we sit in the for-loop trying to synchronize until
// Synchronize() returns true, we will have successfully synchronized the execution
// time of the next event with the wall clock time of the synchronizer.
//
for (;;)
{
uint64_t tsDelay = 0;
uint64_t tsNext = 0;
//
// It is important to understand that m_currentTs is interpreted only as the
// timestamp of the last event we executed. Current time can a bit of a
// slippery concept in realtime mode. What we have here is a discrete event
// simulator, so the last event is, by defintion, executed entirely at a single
// discrete time. This is the definition of m_currentTs. It really has
// nothing to do with the current real time, except that we are trying to arrange
// that at the instant of the beginning of event execution, the current real time
// and m_currentTs coincide.
//
// We use tsNow as the indication of the current real time.
//
uint64_t tsNow;
{
CriticalSection cs (m_mutex);
//
// Since we are in realtime mode, the time to delay has got to be the
// difference between the current realtime and the timestamp of the next
// event. Since m_currentTs is actually the timestamp of the last event we
// executed, it's not particularly meaningful for us here since real time has
// certainly elapsed since it was last updated.
//
// It is possible that the current realtime has drifted past the next event
// time so we need to be careful about that and not delay in that case.
//
NS_ASSERT_MSG (m_synchronizer->Realtime (),
"RealtimeSimulatorImpl::ProcessOneEvent (): Synchronizer reports not Realtime ()");
//
// tsNow is set to the normalized current real time. When the simulation was
// started, the current real time was effectively set to zero; so tsNow is
// the current "real" simulation time.
//
// tsNext is the simulation time of the next event we want to execute.
//
tsNow = m_synchronizer->GetCurrentRealtime ();
tsNext = NextTs ();
//
// tsDelay is therefore the real time we need to delay in order to bring the
// real time in sync with the simulation time. If we wait for this amount of
// real time, we will accomplish moving the simulation time at the same rate
// as the real time. This is typically called "pacing" the simulation time.
//
// We do have to be careful if we are falling behind. If so, tsDelay must be
// zero. If we're late, don't dawdle.
//
if (tsNext <= tsNow)
{
tsDelay = 0;
}
else
{
tsDelay = tsNext - tsNow;
}
//
// We've figured out how long we need to delay in order to pace the
// simulation time with the real time. We're going to sleep, but need
// to work with the synchronizer to make sure we're awakened if something
// external happens (like a packet is received). This next line resets
// the synchronizer so that any future event will cause it to interrupt.
//
m_synchronizer->SetCondition (false);
}
//
// We have a time to delay. This time may actually not be valid anymore
// since we released the critical section immediately above, and a real-time
// ScheduleReal or ScheduleRealNow may have snuck in, well, between the
// closing brace above and this comment so to speak. If this is the case,
// that schedule operation will have done a synchronizer Signal() that
// will set the condition variable to true and cause the Synchronize call
// below to return immediately.
//
// It's easiest to understand if you just consider a short tsDelay that only
// requires a SpinWait down in the synchronizer. What will happen is that
// whan Synchronize calls SpinWait, SpinWait will look directly at its
// condition variable. Note that we set this condition variable to false
// inside the critical section above.
//
// SpinWait will go into a forever loop until either the time has expired or
// until the condition variable becomes true. A true condition indicates that
// the wait should stop. The condition is set to true by one of the Schedule
// methods of the simulator; so if we are in a wait down in Synchronize, and
// a Simulator::ScheduleReal is done, the wait down in Synchronize will exit and
// Synchronize will return false. This means we have not actually synchronized
// to the event expiration time. If no real-time schedule operation is done
// while down in Synchronize, the wait will time out and Synchronize will return
// true. This indicates that we have synchronized to the event time.
//
// So we need to stay in this for loop, looking for the next event timestamp and
// attempting to sleep until its due. If we've slept until the timestamp is due,
// Synchronize returns true and we break out of the sync loop. If an external
// event happens that requires a re-schedule, Synchronize returns false and
// we re-evaluate our timing by continuing in the loop.
//
// It is expected that tsDelay become shorter as external events interrupt our
// waits.
//
if (m_synchronizer->Synchronize (tsNow, tsDelay))
{
NS_LOG_LOGIC ("Interrupted ...");
break;
}
//
// If we get to this point, we have been interrupted during a wait by a real-time
// schedule operation. This means all bets are off regarding tsDelay and we need
// to re-evaluate what it is we want to do. We'll loop back around in the
// for-loop and start again from scratch.
//
}
//
// If we break out of the for-loop above, we have waited until the time specified
// by the event that was at the head of the event list when we started the process.
// Since there is a bunch of code that was executed outside a critical section (the
// Synchronize call) we cannot be sure that the event at the head of the event list
// is the one we think it is. What we can be sure of is that it is time to execute
// whatever event is at the head of this list if the list is in time order.
//
Scheduler::Event next;
{
CriticalSection cs (m_mutex);
//
// We do know we're waiting for an event, so there had better be an event on the
// event queue. Let's pull it off. When we release the critical section, the
// event we're working on won't be on the list and so subsequent operations won't
// mess with us.
//
NS_ASSERT_MSG (m_events->IsEmpty () == false,
"RealtimeSimulatorImpl::ProcessOneEvent(): event queue is empty");
next = m_events->RemoveNext ();
--m_unscheduledEvents;
//
// We cannot make any assumption that "next" is the same event we originally waited
// for. We can only assume that only that it must be due and cannot cause time
// to move backward.
//
NS_ASSERT_MSG (next.key.m_ts >= m_currentTs,
"RealtimeSimulatorImpl::ProcessOneEvent(): "
"next.GetTs() earlier than m_currentTs (list order error)");
NS_LOG_LOGIC ("handle " << next.key.m_ts);
//
// Update the current simulation time to be the timestamp of the event we're
// executing. From the rest of the simulation's point of view, simulation time
// is frozen until the next event is executed.
//
m_currentTs = next.key.m_ts;
m_currentUid = next.key.m_uid;
//
// We're about to run the event and we've done our best to synchronize this
// event execution time to real time. Now, if we're in SYNC_HARD_LIMIT mode
// we have to decide if we've done a good enough job and if we haven't, we've
// been asked to commit ritual suicide.
//
// We check the simulation time against the current real time to make this
// judgement.
//
if (m_synchronizationMode == SYNC_HARD_LIMIT)
{
uint64_t tsFinal = m_synchronizer->GetCurrentRealtime ();
uint64_t tsJitter;
if (tsFinal >= m_currentTs)
{
tsJitter = tsFinal - m_currentTs;
}
else
{
tsJitter = m_currentTs - tsFinal;
}
if (tsJitter > static_cast<uint64_t>(m_hardLimit.GetTimeStep ()))
{
NS_FATAL_ERROR ("RealtimeSimulatorImpl::ProcessOneEvent (): "
"Hard real-time limit exceeded (jitter = " << tsJitter << ")");
}
}
}
//
// We have got the event we're about to execute completely disentangled from the
// event list so we can execute it outside a critical section without fear of someone
// changing things out from under us.
EventImpl *event = next.impl;
m_synchronizer->EventStart ();
event->Invoke ();
m_synchronizer->EventEnd ();
event->Unref ();
}
bool
RealtimeSimulatorImpl::IsFinished (void) const
{
NS_LOG_FUNCTION_NOARGS ();
bool rc;
{
CriticalSection cs (m_mutex);
rc = m_events->IsEmpty () || m_stop;
}
return rc;
}
//
// Peeks into event list. Should be called with critical section locked.
//
uint64_t
RealtimeSimulatorImpl::NextTs (void) const
{
NS_LOG_FUNCTION_NOARGS ();
NS_ASSERT_MSG (m_events->IsEmpty () == false,
"RealtimeSimulatorImpl::NextTs(): event queue is empty");
Scheduler::Event ev = m_events->PeekNext ();
return ev.key.m_ts;
}
//
// Calls NextTs(). Should be called with critical section locked.
//
Time
RealtimeSimulatorImpl::Next (void) const
{
NS_LOG_FUNCTION_NOARGS ();
return TimeStep (NextTs ());
}
void
RealtimeSimulatorImpl::Run (void)
{
NS_LOG_FUNCTION_NOARGS ();
NS_ASSERT_MSG (m_running == false,
"RealtimeSimulatorImpl::Run(): Simulator already running");
m_stop = false;
m_running = true;
m_synchronizer->SetOrigin (m_currentTs);
for (;;)
{
bool done = false;
{
CriticalSection cs (m_mutex);
//
// In all cases we stop when the event list is empty. If you are doing a
// realtime simulation and you want it to extend out for some time, you must
// call StopAt. In the realtime case, this will stick a placeholder event out
// at the end of time.
//
if (m_stop || m_events->IsEmpty ())
{
done = true;
}
}
if (done)
{
break;
}
ProcessOneEvent ();
}
//
// If the simulator stopped naturally by lack of events, make a
// consistency test to check that we didn't lose any events along the way.
//
{
CriticalSection cs (m_mutex);
NS_ASSERT_MSG (m_events->IsEmpty () == false || m_unscheduledEvents == 0,
"RealtimeSimulatorImpl::Run(): Empty queue and unprocessed events");
}
m_running = false;
}
bool
RealtimeSimulatorImpl::Running (void) const
{
NS_LOG_FUNCTION_NOARGS ();
return m_running;
}
bool
RealtimeSimulatorImpl::Realtime (void) const
{
NS_LOG_FUNCTION_NOARGS ();
return m_synchronizer->Realtime ();
}
//
// This will run the first event on the queue without considering any realtime
// synchronization. It's mainly implemented to allow simulations requiring
// the multithreaded ScheduleRealtimeNow() functions the possibility of driving
// the simulation from their own event loop.
//
// It is expected that if there are any realtime requirements, the responsibility
// for synchronizing with real time in an external event loop will be picked up
// by that loop. For example, they may call Simulator::Next() to find the
// execution time of the next event and wait for that time somehow -- then call
// RunOneEvent to fire the event.
//
void
RealtimeSimulatorImpl::RunOneEvent (void)
{
NS_LOG_FUNCTION_NOARGS ();
NS_ASSERT_MSG (m_running == false,
"RealtimeSimulatorImpl::RunOneEvent(): An internal simulator event loop is running");
EventImpl *event = 0;
//
// Run this in a critical section in case there's another thread around that
// may be inserting things onto the event list.
//
{
CriticalSection cs (m_mutex);
Scheduler::Event next = m_events->RemoveNext ();
NS_ASSERT (next.key.m_ts >= m_currentTs);
--m_unscheduledEvents;
NS_LOG_LOGIC ("handle " << next.key.m_ts);
m_currentTs = next.key.m_ts;
m_currentUid = next.key.m_ts;
event = next.impl;
}
event->Invoke ();
event->Unref ();
}
void
RealtimeSimulatorImpl::Stop (void)
{
NS_LOG_FUNCTION_NOARGS ();
m_stop = true;
}
//
// Schedule an event for a _relative_ time in the future.
//
EventId
RealtimeSimulatorImpl::Schedule (Time const &time, EventImpl *impl)
{
NS_LOG_FUNCTION (time << impl);
Scheduler::Event ev;
{
CriticalSection cs (m_mutex);
//
// This is the reason we had to bring the absolute time calcualtion in from the
// simulator.h into the implementation. Since the implementations may be
// multi-threaded, we need this calculation to be atomic. You can see it is
// here since we are running in a CriticalSection.
//
Time tAbsolute = Simulator::Now () + time;
NS_ASSERT_MSG (tAbsolute.IsPositive (), "RealtimeSimulatorImpl::Schedule(): Negative time");
NS_ASSERT_MSG (tAbsolute >= TimeStep (m_currentTs), "RealtimeSimulatorImpl::Schedule(): time < m_currentTs");
ev.impl = impl;
ev.key.m_ts = (uint64_t) tAbsolute.GetTimeStep ();
ev.key.m_uid = m_uid;
m_uid++;
++m_unscheduledEvents;
m_events->Insert (ev);
m_synchronizer->Signal ();
}
return EventId (impl, ev.key.m_ts, ev.key.m_uid);
}
EventId
RealtimeSimulatorImpl::ScheduleNow (EventImpl *impl)
{
NS_LOG_FUNCTION_NOARGS ();
Scheduler::Event ev;
{
CriticalSection cs (m_mutex);
ev.impl = impl;
ev.key.m_ts = m_currentTs;
ev.key.m_uid = m_uid;
m_uid++;
++m_unscheduledEvents;
m_events->Insert (ev);
m_synchronizer->Signal ();
}
return EventId (impl, ev.key.m_ts, ev.key.m_uid);
}
Time
RealtimeSimulatorImpl::Now (void) const
{
return TimeStep (m_currentTs);
}
//
// Schedule an event for a _relative_ time in the future.
//
void
RealtimeSimulatorImpl::ScheduleRealtime (Time const &time, EventImpl *impl)
{
NS_LOG_FUNCTION (time << impl);
{
CriticalSection cs (m_mutex);
uint64_t ts = m_synchronizer->GetCurrentRealtime () + time.GetTimeStep ();
NS_ASSERT_MSG (ts >= m_currentTs, "RealtimeSimulatorImpl::ScheduleRealtime(): schedule for time < m_currentTs");
Scheduler::Event ev;
ev.impl = impl;
ev.key.m_ts = ts;
ev.key.m_uid = m_uid;
m_uid++;
++m_unscheduledEvents;
m_events->Insert (ev);
m_synchronizer->Signal ();
}
}
void
RealtimeSimulatorImpl::ScheduleRealtimeNow (EventImpl *impl)
{
NS_LOG_FUNCTION_NOARGS ();
{
CriticalSection cs (m_mutex);
//
// If the simulator is running, we're pacing and have a meaningful
// realtime clock. If we're not, then m_currentTs is were we stopped.
//
uint64_t ts = m_running ? m_synchronizer->GetCurrentRealtime () : m_currentTs;
NS_ASSERT_MSG (ts >= m_currentTs, "RealtimeSimulatorImpl::ScheduleRealtimeNow(): schedule for time < m_currentTs");
Scheduler::Event ev;
ev.impl = impl;
ev.key.m_ts = ts;
ev.key.m_uid = m_uid;
m_uid++;
++m_unscheduledEvents;
m_events->Insert (ev);
m_synchronizer->Signal ();
}
}
Time
RealtimeSimulatorImpl::RealtimeNow (void) const
{
return TimeStep (m_synchronizer->GetCurrentRealtime ());
}
EventId
RealtimeSimulatorImpl::ScheduleDestroy (EventImpl *impl)
{
NS_LOG_FUNCTION_NOARGS ();
EventId id;
{
CriticalSection cs (m_mutex);
//
// Time doesn't really matter here (especially in realtime mode). It is
// overridden by the uid of 2 which identifies this as an event to be
// executed at Simulator::Destroy time.
//
id = EventId (Ptr<EventImpl> (impl, false), m_currentTs, 2);
m_destroyEvents.push_back (id);
m_uid++;
}
return id;
}
Time
RealtimeSimulatorImpl::GetDelayLeft (const EventId &id) const
{
//
// If the event has expired, there is no delay until it runs. It is not the
// case that there is a negative time until it runs.
//
if (IsExpired (id))
{
return TimeStep (0);
}
return TimeStep (id.GetTs () - m_currentTs);
}
void
RealtimeSimulatorImpl::Remove (const EventId &id)
{
if (id.GetUid () == 2)
{
// destroy events.
for (DestroyEvents::iterator i = m_destroyEvents.begin ();
i != m_destroyEvents.end ();
i++)
{
if (*i == id)
{
m_destroyEvents.erase (i);
break;
}
}
return;
}
if (IsExpired (id))
{
return;
}
{
CriticalSection cs (m_mutex);
Scheduler::Event event;
event.impl = id.PeekEventImpl ();
event.key.m_ts = id.GetTs ();
event.key.m_uid = id.GetUid ();
m_events->Remove (event);
--m_unscheduledEvents;
event.impl->Cancel ();
event.impl->Unref ();
}
}
void
RealtimeSimulatorImpl::Cancel (const EventId &id)
{
if (IsExpired (id) == false)
{
id.PeekEventImpl ()->Cancel ();
}
}
bool
RealtimeSimulatorImpl::IsExpired (const EventId &ev) const
{
if (ev.GetUid () == 2)
{
// destroy events.
for (DestroyEvents::const_iterator i = m_destroyEvents.begin ();
i != m_destroyEvents.end (); i++)
{
if (*i == ev)
{
return false;
}
}
return true;
}
//
// If the time of the event is less than the current timestamp of the
// simulator, the simulator has gone past the invocation time of the
// event, so the statement ev.GetTs () < m_currentTs does mean that
// the event has been fired even in realtime mode.
//
// The same is true for the next line involving the m_currentUid.
//
if (ev.PeekEventImpl () == 0 ||
ev.GetTs () < m_currentTs ||
(ev.GetTs () == m_currentTs && ev.GetUid () <= m_currentUid) ||
ev.PeekEventImpl ()->IsCancelled ())
{
return true;
}
else
{
return false;
}
}
Time
RealtimeSimulatorImpl::GetMaximumSimulationTime (void) const
{
// XXX: I am fairly certain other compilers use other non-standard
// post-fixes to indicate 64 bit constants.
return TimeStep (0x7fffffffffffffffLL);
}
void
RealtimeSimulatorImpl::SetSynchronizationMode (enum SynchronizationMode mode)
{
NS_LOG_FUNCTION (mode);
m_synchronizationMode = mode;
}
RealtimeSimulatorImpl::SynchronizationMode
RealtimeSimulatorImpl::GetSynchronizationMode (void) const
{
NS_LOG_FUNCTION_NOARGS ();
return m_synchronizationMode;
}
void
RealtimeSimulatorImpl::SetHardLimit (Time limit)
{
NS_LOG_FUNCTION (limit);
m_hardLimit = limit;
}
Time
RealtimeSimulatorImpl::GetHardLimit (void) const
{
NS_LOG_FUNCTION_NOARGS ();
return m_hardLimit;
}
}; // namespace ns3
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