Class used for synchronizing the simulation events to a real-time "wall clock" using Posix clock functions. More...

#include "wall-clock-synchronizer.h"

Inheritance diagram for ns3::WallClockSynchronizer:

Collaboration diagram for ns3::WallClockSynchronizer:

Public Member Functions
	WallClockSynchronizer ()
	Constructor.

	~WallClockSynchronizer () override
	Destructor.

Public Member Functions inherited from ns3::Synchronizer
	Synchronizer ()
	Constructor.

	~Synchronizer () override
	Destructor.

uint64_t	EventEnd ()
	Ask the synchronizer to return the time step between the instant remembered during EventStart and now.

void	EventStart ()
	Ask the synchronizer to remember what time it is.

uint64_t	GetCurrentRealtime ()
	Retrieve the value of the origin of the underlying normalized wall clock time in simulator timestep units.

int64_t	GetDrift (uint64_t ts)
	Retrieve the difference between the real time clock used to synchronize the simulation and the simulation time (in Time resolution units).

uint64_t	GetOrigin ()
	Retrieve the value of the origin of the simulation time in Time.resolution units.

bool	Realtime ()
	Return true if this synchronizer is actually synchronizing to a realtime clock.

void	SetCondition (bool cond)
	Set the condition variable that tells a possible simulator thread waiting in the Synchronize method that an event has happened which demands a reevaluation of the wait time.

void	SetOrigin (uint64_t ts)
	Establish a correspondence between a simulation time and the synchronizer real time.

void	Signal ()
	Tell a possible simulator thread waiting in the Synchronize method that an event has happened which demands a reevaluation of the wait time.

bool	Synchronize (uint64_t tsCurrent, uint64_t tsDelay)
	Wait until the real time is in sync with the specified simulation time or until the synchronizer is Signalled.

Public Member Functions inherited from ns3::Object
	Object ()
	Constructor.

	~Object () override
	Destructor.

void	AggregateObject (Ptr< Object > other)
	Aggregate two Objects together.

void	Dispose ()
	Dispose of this Object.

AggregateIterator	GetAggregateIterator () const
	Get an iterator to the Objects aggregated to this one.

TypeId	GetInstanceTypeId () const override
	Get the most derived TypeId for this Object.

template<typename T >
Ptr< T >	GetObject () const
	Get a pointer to the requested aggregated Object.

template<>
Ptr< Object >	GetObject () const
	Specialization of () for objects of type ns3::Object.

template<typename T >
Ptr< T >	GetObject (TypeId tid) const
	Get a pointer to the requested aggregated Object by TypeId.

template<>
Ptr< Object >	GetObject (TypeId tid) const
	Specialization of (TypeId tid) for objects of type ns3::Object.

void	Initialize ()
	Invoke DoInitialize on all Objects aggregated to this one.

bool	IsInitialized () const
	Check if the object has been initialized.

void	UnidirectionalAggregateObject (Ptr< Object > other)
	Aggregate an Object to another Object.

Public Member Functions inherited from ns3::SimpleRefCount< Object, ObjectBase, ObjectDeleter >
	SimpleRefCount ()
	Default constructor.

	SimpleRefCount (const SimpleRefCount &o)
	Copy constructor.

uint32_t	GetReferenceCount () const
	Get the reference count of the object.

SimpleRefCount &	operator= (const SimpleRefCount &o)
	Assignment operator.

void	Ref () const
	Increment the reference count.

void	Unref () const
	Decrement the reference count.

Public Member Functions inherited from ns3::ObjectBase
virtual	~ObjectBase ()
	Virtual destructor.

void	GetAttribute (std::string name, AttributeValue &value, bool permissive=false) const
	Get the value of an attribute, raising fatal errors if unsuccessful.

bool	GetAttributeFailSafe (std::string name, AttributeValue &value) const
	Get the value of an attribute without raising errors.

void	SetAttribute (std::string name, const AttributeValue &value)
	Set a single attribute, raising fatal errors if unsuccessful.

bool	SetAttributeFailSafe (std::string name, const AttributeValue &value)
	Set a single attribute without raising errors.

bool	TraceConnect (std::string name, std::string context, const CallbackBase &cb)
	Connect a TraceSource to a Callback with a context.

bool	TraceConnectWithoutContext (std::string name, const CallbackBase &cb)
	Connect a TraceSource to a Callback without a context.

bool	TraceDisconnect (std::string name, std::string context, const CallbackBase &cb)
	Disconnect from a TraceSource a Callback previously connected with a context.

bool	TraceDisconnectWithoutContext (std::string name, const CallbackBase &cb)
	Disconnect from a TraceSource a Callback previously connected without a context.

Static Public Member Functions
static TypeId	GetTypeId ()
	Get the registered TypeId for this class.

Static Public Member Functions inherited from ns3::Synchronizer
static TypeId	GetTypeId ()
	Get the registered TypeId for this class.

Static Public Member Functions inherited from ns3::Object
static TypeId	GetTypeId ()
	Register this type.

Static Public Member Functions inherited from ns3::ObjectBase
static TypeId	GetTypeId ()
	Get the type ID.

Static Public Attributes
static const uint64_t	NS_PER_SEC = (uint64_t)1000000000
	Conversion constant between ns and s.

static const uint64_t	US_PER_NS = (uint64_t)1000
	Conversion constant between μs and ns.

static const uint64_t	US_PER_SEC = (uint64_t)1000000
	Conversion constant between μs and seconds.

Protected Member Functions
uint64_t	DoEventEnd () override
	Return the amount of real time elapsed since the last call to EventStart.

void	DoEventStart () override
	Record the normalized real time at which the current event is starting execution.

uint64_t	DoGetCurrentRealtime () override
	Retrieve the value of the origin of the underlying normalized wall clock time in Time resolution units.

int64_t	DoGetDrift (uint64_t ns) override
	Get the drift between the real time clock used to synchronize the simulation and the current simulation time.

bool	DoRealtime () override
	Return `true` if this synchronizer is actually synchronizing to a realtime clock.

void	DoSetCondition (bool cond) override
	Set the condition variable to tell a possible simulator thread waiting in the Synchronize method that an event has happened which demands a reevaluation of the wait time.

void	DoSetOrigin (uint64_t ns) override
	Establish a correspondence between a simulation time and a wall-clock (real) time.

void	DoSignal () override
	Tell a possible simulator thread waiting in the DoSynchronize method that an event has happened which demands a reevaluation of the wait time.

bool	DoSynchronize (uint64_t nsCurrent, uint64_t nsDelay) override
	Wait until the real time is in sync with the specified simulation time.

uint64_t	DriftCorrect (uint64_t nsNow, uint64_t nsDelay)
	Compute a correction to the nominal delay to account for realtime drift since the last DoSynchronize.

uint64_t	GetNormalizedRealtime ()
	Get the current normalized real time, in ns.

uint64_t	GetRealtime ()
	Get the current absolute real time (in ns since the epoch).

bool	SleepWait (uint64_t ns)
	Put our process to sleep for some number of nanoseconds.

bool	SpinWait (uint64_t ns)
	Do a busy-wait until the normalized realtime equals the argument or the condition variable becomes `true`.

Protected Member Functions inherited from ns3::Object
	Object (const Object &o)
	Copy an Object.

virtual void	DoDispose ()
	Destructor implementation.

virtual void	DoInitialize ()
	Initialize() implementation.

virtual void	NotifyNewAggregate ()
	Notify all Objects aggregated to this one of a new Object being aggregated.

Protected Member Functions inherited from ns3::ObjectBase
void	ConstructSelf (const AttributeConstructionList &attributes)
	Complete construction of ObjectBase; invoked by derived classes.

virtual void	NotifyConstructionCompleted ()
	Notifier called once the ObjectBase is fully constructed.

Protected Attributes
bool	m_condition
	The condition state.

std::condition_variable	m_conditionVariable
	Condition variable for thread synchronizer.

uint64_t	m_jiffy
	Size of the system clock tick, as reported by `clock_getres`, in ns.

std::mutex	m_mutex
	Mutex controlling access to the condition variable.

uint64_t	m_nsEventStart
	Time recorded by DoEventStart.

Protected Attributes inherited from ns3::Synchronizer
uint64_t	m_realtimeOriginNano
	The real time, in ns, when SetOrigin was called.

uint64_t	m_simOriginNano
	The simulation time, in ns, when SetOrigin was called.

Additional Inherited Members
Related Symbols inherited from ns3::ObjectBase
static TypeId	GetObjectIid ()
	Ensure the TypeId for ObjectBase gets fully configured to anchor the inheritance tree properly.

Detailed Description

Class used for synchronizing the simulation events to a real-time "wall clock" using Posix clock functions.

This synchronizer is used as part of the RealtimeSimulatorImpl. It is typically not explicitly enabled by users but instead is implicitly enabled when the simulator implementation type is set to real-time; e.g.:

GlobalValue::Bind ("SimulatorImplementationType",

StringValue ("ns3::RealtimeSimulatorImpl"));

ns3::GlobalValue::Bind

static void Bind(std::string name, const AttributeValue &value)

Iterate over the set of GlobalValues until a matching name is found and then set its value with Globa...

Definition global-value.cc:126

ns3::StringValue

Hold variables of type string.

Definition string.h:45

before calling any simulator functions.

There are a couple of more issues at this level. Posix clocks provide access to several clocks we could use as a wall clock. We don't care about time in the sense of 04:30 CEST, we care about some piece of hardware that ticks at some regular period. The most accurate posix clock in this respect is the CLOCK_PROCESS_CPUTIME_ID clock. This is a high-resolution register in the CPU. For example, on Intel machines this corresponds to the timestamp counter (TSC) register. The resolution of this counter will be on the order of nanoseconds.

Now, just because we can measure time in nanoseconds doesn't mean we can put our process to sleep to nanosecond resolution. We are eventually going to use the function clock_nanosleep() to sleep until a simulation Time specified by the caller.

Todo: Add more on jiffies, sleep, processes, etc.

Definition at line 57 of file wall-clock-synchronizer.h.

Constructor & Destructor Documentation

◆ WallClockSynchronizer()

ns3::WallClockSynchronizer::WallClockSynchronizer ( )

Constructor.

Definition at line 37 of file wall-clock-synchronizer.cc.

References m_jiffy, NS_LOG_FUNCTION, and NS_LOG_INFO.

◆ ~WallClockSynchronizer()

ns3::WallClockSynchronizer::~WallClockSynchronizer ( )

override

Destructor.

Definition at line 72 of file wall-clock-synchronizer.cc.

References NS_LOG_FUNCTION.

Member Function Documentation

◆ DoEventEnd()

uint64_t ns3::WallClockSynchronizer::DoEventEnd ( )

overrideprotectedvirtual

Return the amount of real time elapsed since the last call to EventStart.

Returns: The elapsed real time, in ns.

Implements ns3::Synchronizer.

Definition at line 294 of file wall-clock-synchronizer.cc.

References GetNormalizedRealtime(), m_nsEventStart, and NS_LOG_FUNCTION.

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◆ DoEventStart()

void ns3::WallClockSynchronizer::DoEventStart ( )

overrideprotectedvirtual

Record the normalized real time at which the current event is starting execution.

Implements ns3::Synchronizer.

Definition at line 287 of file wall-clock-synchronizer.cc.

References GetNormalizedRealtime(), m_nsEventStart, and NS_LOG_FUNCTION.

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◆ DoGetCurrentRealtime()

uint64_t ns3::WallClockSynchronizer::DoGetCurrentRealtime ( )

overrideprotectedvirtual

Retrieve the value of the origin of the underlying normalized wall clock time in Time resolution units.

Subclasses are expected to implement this method to do the actual real-time-clock-specific work of getting the current time.

Returns: The normalized wall clock time (in nanosecond units).

See also: SetOrigin

Implements ns3::Synchronizer.

Definition at line 85 of file wall-clock-synchronizer.cc.

References GetNormalizedRealtime(), and NS_LOG_FUNCTION.

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◆ DoGetDrift()

int64_t ns3::WallClockSynchronizer::DoGetDrift ( uint64_t ns )

overrideprotectedvirtual

Get the drift between the real time clock used to synchronize the simulation and the current simulation time.

Parameters

[in] ns Simulation time in ns.

Returns: Drift in ns units.

See also: SetOrigin; GetDrift

Implements ns3::Synchronizer.

Definition at line 108 of file wall-clock-synchronizer.cc.

References GetNormalizedRealtime(), and NS_LOG_FUNCTION.

Referenced by DoSynchronize(), and DriftCorrect().

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◆ DoRealtime()

bool ns3::WallClockSynchronizer::DoRealtime ( )

overrideprotectedvirtual

Return true if this synchronizer is actually synchronizing to a realtime clock.

The simulator sometimes needs to know this.

Subclasses are expected to implement this method to tell the outside world whether or not they are synchronizing to a realtime clock.

Returns: true if locked with realtime, false if not.

Implements ns3::Synchronizer.

Definition at line 78 of file wall-clock-synchronizer.cc.

References NS_LOG_FUNCTION.

◆ DoSetCondition()

void ns3::WallClockSynchronizer::DoSetCondition ( bool cond )

overrideprotectedvirtual

Set the condition variable to tell a possible simulator thread waiting in the Synchronize method that an event has happened which demands a reevaluation of the wait time.

Parameters

[in] cond The new value for the condition variable.

See also: SetCondition

Implements ns3::Synchronizer.

Definition at line 280 of file wall-clock-synchronizer.cc.

References m_condition, and NS_LOG_FUNCTION.

◆ DoSetOrigin()

void ns3::WallClockSynchronizer::DoSetOrigin ( uint64_t ns )

overrideprotectedvirtual

Establish a correspondence between a simulation time and a wall-clock (real) time.

There are three timelines involved here: the simulation (virtual) time, the (absolute) wall-clock time and the (relative) synchronizer real time. Calling this method makes a correspondence between the origin of the synchronizer time and the current wall-clock time.

This method is expected to be called at the "instant" before simulation begins. At this point, simulation time = 0, and synchronizer time is set = 0 in this method. We then associate this time with the current value of the real time clock that will be used to actually perform the synchronization.

Subclasses are expected to implement this method to do the actual real-time-clock-specific work of making the correspondence mentioned above. for example, this is where the differences between Time parameters and parameters to clock_nanosleep would be dealt with.

Parameters

[in] ns The simulation time we need to use as the origin (normalized to nanosecond units).

See also: SetOrigin

Implements ns3::Synchronizer.

Definition at line 92 of file wall-clock-synchronizer.cc.

References GetRealtime(), ns3::Synchronizer::m_realtimeOriginNano, NS_LOG_FUNCTION, and NS_LOG_INFO.

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◆ DoSignal()

void ns3::WallClockSynchronizer::DoSignal ( )

overrideprotectedvirtual

Tell a possible simulator thread waiting in the DoSynchronize method that an event has happened which demands a reevaluation of the wait time.

See also: Signal

Implements ns3::Synchronizer.

Definition at line 265 of file wall-clock-synchronizer.cc.

References m_condition, m_conditionVariable, m_mutex, and NS_LOG_FUNCTION.

◆ DoSynchronize()

bool ns3::WallClockSynchronizer::DoSynchronize	(	uint64_t	nsCurrent,
		uint64_t	nsDelay )

overrideprotectedvirtual

Wait until the real time is in sync with the specified simulation time.

This is where the real work of synchronization is done. The nsCurrent argument is the simulation time (in ns). The job of DoSynchronize is to translate from simulation time to synchronizer time (in a perfect world these are the same time) and then figure out how long in real-time it needs to wait until that synchronizer / simulation time comes around.

Subclasses are expected to implement this method to do the actual real-time-clock-specific work of waiting (either busy-waiting or sleeping, or some combination) until the requested simulation time.

Parameters

[in]	nsCurrent	The current simulation time (in nanosecond units).
[in]	nsDelay	The simulation time we need to wait for (normalized to nanosecond units).

Returns: true if the function ran to completion, false if it was interrupted by a Signal.

See also: Synchronize; Signal

Implements ns3::Synchronizer.

Definition at line 148 of file wall-clock-synchronizer.cc.

References DoGetDrift(), DriftCorrect(), m_jiffy, NS_LOG_FUNCTION, NS_LOG_INFO, SleepWait(), and SpinWait().

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◆ DriftCorrect()

uint64_t ns3::WallClockSynchronizer::DriftCorrect	(	uint64_t	nsNow,
		uint64_t	nsDelay )

protected

Compute a correction to the nominal delay to account for realtime drift since the last DoSynchronize.

Parameters

[in]	nsNow	The current simulation time (in nanosecond units).
[in]	nsDelay	The simulation time we need to wait for (normalized to nanosecond units).

Returns: The corrected delay.

Definition at line 336 of file wall-clock-synchronizer.cc.

References DoGetDrift(), and NS_LOG_FUNCTION.

Referenced by DoSynchronize().

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◆ GetNormalizedRealtime()

uint64_t ns3::WallClockSynchronizer::GetNormalizedRealtime ( )

protected

Get the current normalized real time, in ns.

Returns: The current normalized real time, in ns.

Definition at line 375 of file wall-clock-synchronizer.cc.

References GetRealtime(), ns3::Synchronizer::m_realtimeOriginNano, and NS_LOG_FUNCTION.

Referenced by DoEventEnd(), DoEventStart(), DoGetCurrentRealtime(), DoGetDrift(), and SpinWait().

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◆ GetRealtime()

uint64_t ns3::WallClockSynchronizer::GetRealtime ( )

protected

Get the current absolute real time (in ns since the epoch).

Returns: The current real time, in ns.

Definition at line 367 of file wall-clock-synchronizer.cc.

References NS_LOG_FUNCTION.

Referenced by DoSetOrigin(), and GetNormalizedRealtime().

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◆ GetTypeId()

TypeId ns3::WallClockSynchronizer::GetTypeId ( )

static

Get the registered TypeId for this class.

Returns: The TypeId.

Definition at line 30 of file wall-clock-synchronizer.cc.

References ns3::TypeId::SetParent().

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◆ SleepWait()

bool ns3::WallClockSynchronizer::SleepWait ( uint64_t ns )

protected

Put our process to sleep for some number of nanoseconds.

Typically this will be some time equal to an integral number of jiffies. We will usually follow a call to SleepWait with a call to SpinWait to get the kind of accuracy we want.

We have to have some mechanism to wake up this sleep in case an external event happens that causes a Schedule event in the simulator. This newly scheduled event might be before the time we are waiting until, so we have to break out of both the SleepWait and the following SpinWait to go back and reschedule/resynchronize taking the new event into account. The condition we have saved in m_condition, along with the condition variable m_conditionVariable take care of this for us.

This call will return if the timeout expires OR if the condition is set true by a call to SetCondition (true) followed by a call to Signal(). In either case, we are done waiting. If the timeout happened, we return true; if a Signal happened we return false.

Parameters

[in] ns The target normalized real time we should wait for.

Returns: true if we reached the target time, false if we returned because the condition was set.

Definition at line 322 of file wall-clock-synchronizer.cc.

References m_condition, m_conditionVariable, m_mutex, and NS_LOG_FUNCTION.

Referenced by DoSynchronize().

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◆ SpinWait()

bool ns3::WallClockSynchronizer::SpinWait ( uint64_t ns )

protected

Do a busy-wait until the normalized realtime equals the argument or the condition variable becomes true.

The condition becomes true if an outside entity (a network device receives a packet), sets the condition and signals the scheduler it needs to re-evaluate.

Parameters

[in] ns The target normalized real time we should wait for.

Returns: true if we reached the target time, false if we returned because the condition was set.

Definition at line 301 of file wall-clock-synchronizer.cc.

References GetNormalizedRealtime(), m_condition, and NS_LOG_FUNCTION.

Referenced by DoSynchronize().

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Member Data Documentation

◆ m_condition

bool ns3::WallClockSynchronizer::m_condition

protected

The condition state.

Definition at line 163 of file wall-clock-synchronizer.h.

Referenced by DoSetCondition(), DoSignal(), SleepWait(), and SpinWait().

◆ m_conditionVariable

std::condition_variable ns3::WallClockSynchronizer::m_conditionVariable

protected

Condition variable for thread synchronizer.

Definition at line 159 of file wall-clock-synchronizer.h.

Referenced by DoSignal(), and SleepWait().

◆ m_jiffy

uint64_t ns3::WallClockSynchronizer::m_jiffy

protected

Size of the system clock tick, as reported by clock_getres, in ns.

Definition at line 154 of file wall-clock-synchronizer.h.

Referenced by WallClockSynchronizer(), and DoSynchronize().

◆ m_mutex

std::mutex ns3::WallClockSynchronizer::m_mutex

protected

Mutex controlling access to the condition variable.

Definition at line 161 of file wall-clock-synchronizer.h.

Referenced by DoSignal(), and SleepWait().

◆ m_nsEventStart

uint64_t ns3::WallClockSynchronizer::m_nsEventStart

protected

Time recorded by DoEventStart.

Definition at line 156 of file wall-clock-synchronizer.h.

Referenced by DoEventEnd(), and DoEventStart().

◆ NS_PER_SEC

const uint64_t ns3::WallClockSynchronizer::NS_PER_SEC = (uint64_t)1000000000

static

Conversion constant between ns and s.

Definition at line 76 of file wall-clock-synchronizer.h.

◆ US_PER_NS

const uint64_t ns3::WallClockSynchronizer::US_PER_NS = (uint64_t)1000

static

Conversion constant between μs and ns.

Definition at line 72 of file wall-clock-synchronizer.h.

◆ US_PER_SEC

const uint64_t ns3::WallClockSynchronizer::US_PER_SEC = (uint64_t)1000000

static

Conversion constant between μs and seconds.

Definition at line 74 of file wall-clock-synchronizer.h.

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

src/core/model/wall-clock-synchronizer.h
src/core/model/wall-clock-synchronizer.cc

Public Member Functions

Static Public Member Functions

Static Public Attributes

Protected Member Functions

Protected Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ WallClockSynchronizer()

◆ ~WallClockSynchronizer()

Member Function Documentation

◆ DoEventEnd()

◆ DoEventStart()

◆ DoGetCurrentRealtime()

◆ DoGetDrift()

◆ DoRealtime()

◆ DoSetCondition()

◆ DoSetOrigin()

◆ DoSignal()

◆ DoSynchronize()

◆ DriftCorrect()

◆ GetNormalizedRealtime()

◆ GetRealtime()

◆ GetTypeId()

◆ SleepWait()

◆ SpinWait()

Member Data Documentation

◆ m_condition

◆ m_conditionVariable

◆ m_jiffy

◆ m_mutex

◆ m_nsEventStart

◆ NS_PER_SEC

◆ US_PER_NS

◆ US_PER_SEC