stk::sync::ConditionVariable Class Reference

Condition Variable primitive for signaling between tasks based on specific predicates. More...

#include <stk_sync_cv.h>

Inheritance diagram for stk::sync::ConditionVariable:

Collaboration diagram for stk::sync::ConditionVariable:

Public Member Functions
	ConditionVariable ()
	~ConditionVariable ()
	Destructor.
bool	Wait (IMutex &mutex, Timeout timeout_ticks=WAIT_INFINITE)
	Wait for a signal.
void	NotifyOne ()
	Wake one waiting task.
void	NotifyOne_CS ()
	Wake one waiting task.
void	NotifyAll ()
	Wake all waiting tasks.
void	NotifyAll_CS ()
	Wake all waiting tasks.
void	SetTraceName (const char *name)
	Set name.
const char *	GetTraceName () const
	Get name.

Private Types
typedef DLHeadType	ListHeadType
	List head type for ISyncObject elements.
typedef DLEntryType	ListEntryType
	List entry type of ISyncObject elements.
enum
	A tag for type-safe casts done by CastListEntryToParent. More...
typedef DListEntry< ISyncObject, TClosedLoop >	DLEntryType
	Convenience alias for this entry type. Used to avoid repeating the full template spelling.
typedef DListHead< ISyncObject, TClosedLoop >	DLHeadType
	Convenience alias for the corresponding list head type.

Private Member Functions
	ConditionVariable (const ConditionVariable &)=delete
ConditionVariable &	operator= (const ConditionVariable &)=delete
virtual void	AddWaitObject (IWaitObject *wobj)
	Called by kernel when a new task starts waiting on this event.
virtual void	RemoveWaitObject (IWaitObject *wobj)
	Called by kernel when a waiting task is being removed (timeout expired, wait aborted, task terminated etc.).
virtual bool	Tick (Timeout elapsed_ticks)
	Called by kernel on every system tick to handle timeout logic of waiting tasks.
Weight	FindWeightHigherThan (Weight comp) const
	Find higher weight within linked wait objects.
void	WakeOne ()
	Wake the first task in the wait list (FIFO order).
void	WakeAll ()
	Wake all tasks currently in the wait list.
DLHeadType *	GetHead ()
	Get the list head this entry currently belongs to.
DLEntryType *	GetNext ()
	Get the next entry in the list.
DLEntryType *	GetPrev ()
	Get the previous entry in the list.
bool	IsLinked () const
	Check whether this entry is currently a member of any list.
	operator ISyncObject * ()
	Implicit conversion to a mutable pointer to the host object (T).
	operator const ISyncObject * () const
	Implicit conversion to a const pointer to the host object (T).
void	Link (DLHeadType *head, DLEntryType *next, DLEntryType *prev)
	Wire this entry into a list between prev and next.
void	Unlink ()
	Remove this entry from its current list.

Private Attributes
IWaitObject::ListHeadType	m_wait_list
	tasks blocked on this object
DLHeadType *	m_head
	Owning list head, or NULL when the entry is not linked.
DLEntryType *	m_next
	Next entry in the list, or NULL (open list boundary) / first entry (closed loop).
DLEntryType *	m_prev
	Previous entry in the list, or NULL (open list boundary) / last entry (closed loop).

Detailed Description

Condition Variable primitive for signaling between tasks based on specific predicates.

Condition Variables are synchronization primitives that enable tasks to wait until a particular condition (predicate) is met. They must be used in conjunction with an IMutex-compatible lock to protect the shared state.

Note

This implementation follows the Monitor pattern: the Wait() operation atomically releases the associated lock and suspends the task. Upon waking (via signal or timeout), the lock is automatically re-acquired before the function returns.

// Usage example: Producer-Consumer pattern using a fixed-size pipe
stk::sync::Mutex                        g_Mtx;
stk::sync::ConditionVariable            g_Cond;
stk::sync::Pipe<int, 16>                g_Pipe;
 
void Task_Consumer() {
    g_Mtx.Lock();
    while (g_Pipe.IsEmpty()) {
        // releases g_Mtx and sleeps; re-acquires g_Mtx upon waking
        if (!g_Cond.Wait(g_Mtx, 1000)) {
            break; // timeout handling
        }
    }
    int data;
    if (g_Pipe.Read(data)) {
        // ... process data ...
    }
    g_Mtx.Unlock();
}
 
void Task_Producer() {
    g_Mtx.Lock();
    g_Pipe.Write(42);
    // wake one waiting task
    g_Cond.NotifyOne();
    g_Mtx.Unlock();
}

See also

Mutex, ISyncObject, IWaitObject, IKernelService::Wait

Note

Only available when kernel is compiled with KERNEL_SYNC mode enabled.

Definition at line 67 of file stk_sync_cv.h.

Member Typedef Documentation

DLEntryType

typedef DListEntry<ISyncObject, TClosedLoop> stk::util::DListEntry< ISyncObject, TClosedLoop >::DLEntryType

inherited

Convenience alias for this entry type. Used to avoid repeating the full template spelling.

Definition at line 75 of file stk_linked_list.h.

DLHeadType

typedef DListHead<ISyncObject, TClosedLoop> stk::util::DListEntry< ISyncObject, TClosedLoop >::DLHeadType

inherited

Convenience alias for the corresponding list head type.

Definition at line 80 of file stk_linked_list.h.

ListEntryType

typedef DLEntryType stk::ISyncObject::ListEntryType

inherited

List entry type of ISyncObject elements.

Definition at line 451 of file stk_common.h.

ListHeadType

typedef DLHeadType stk::ISyncObject::ListHeadType

inherited

List head type for ISyncObject elements.

Definition at line 446 of file stk_common.h.

Member Enumeration Documentation

anonymous enum

anonymous enum

inherited

A tag for type-safe casts done by CastListEntryToParent.

See also

CastListEntryToParent.

Definition at line 70 of file stk_linked_list.h.

{ DLEntryTag = 1 };

Constructor & Destructor Documentation

ConditionVariable() [1/2]

stk::sync::ConditionVariable::ConditionVariable ( )

inlineexplicit

Definition at line 70 of file stk_sync_cv.h.

    {}

Referenced by ConditionVariable().

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~ConditionVariable()

stk::sync::ConditionVariable::~ConditionVariable ( )

inline

Destructor.

Note

If tasks are still waiting at destruction time it is considered a logical error (dangling waiters). An assertion is triggered in debug builds.

MISRA deviation: [STK-DEV-005] Rule 10-3-2.

Definition at line 78 of file stk_sync_cv.h.

    {
        STK_ASSERT(m_wait_list.IsEmpty()); // API contract: must not be destroyed with waiting tasks
    }

References stk::ISyncObject::m_wait_list, STK_ASSERT, and STK_VIRT_DTOR.

ConditionVariable() [2/2]

stk::sync::ConditionVariable::ConditionVariable ( const ConditionVariable & )

privatedelete

References ConditionVariable().

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Member Function Documentation

AddWaitObject()

virtual void stk::ISyncObject::AddWaitObject ( IWaitObject * wobj )

inlinevirtualinherited

Called by kernel when a new task starts waiting on this event.

Parameters

[in]

wobj

Wait object representing blocked task.

Note

Must be called inside the critical section (see hw::CriticalSection, sync::ScopedCrticalSection).

Definition at line 457 of file stk_common.h.

    {
        STK_ASSERT(wobj->GetHead() == nullptr);
        m_wait_list.LinkBack(wobj);
    }

References stk::util::DListEntry< T, TClosedLoop >::GetHead(), m_wait_list, and STK_ASSERT.

Referenced by stk::Kernel< TMode, TSize, TStrategy, TPlatform >::KernelTask::WaitObject::SetupWait().

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FindWeightHigherThan()

Weight stk::ISyncObject::FindWeightHigherThan ( Weight comp ) const

inlineinherited

Find higher weight within linked wait objects.

Implementation of ISyncObject::Tick, see ISyncObject. Placed here as it depends on GetUserTaskFromTid.

Parameters

[in]

comp

Weight to compare with.

Returns

Higher weight value than comp, or NO_WEIGHT if there is no object with a higher weight.

Note

Must be called inside the critical section (see hw::CriticalSection, sync::ScopedCrticalSection).

Definition at line 214 of file stk_helper.h.

{
    Weight max_weight = NO_WEIGHT;
    const IWaitObject *itr = util::DListCast::ListEntryToParent<const IWaitObject>(m_wait_list.GetFirst());     
 
    while (itr != nullptr)
    {
        const Weight w = GetUserTaskFromTid(itr->GetTid())->GetWeight();
        if (w > max_weight)
        {
            max_weight = w;
        }
            
        itr = util::DListCast::ListEntryToParent<const IWaitObject>(itr->GetNext());
    }
 
    return ((max_weight > comp) ? max_weight : NO_WEIGHT);
}

References stk::util::DListEntry< T, TClosedLoop >::GetNext(), stk::IWaitObject::GetTid(), stk::GetUserTaskFromTid(), stk::ITask::GetWeight(), stk::util::DListCast::ListEntryToParent(), m_wait_list, and stk::NO_WEIGHT.

Referenced by stk::Kernel< stk::KERNEL_DYNAMIC|stk::KERNEL_SYNC|stk::KERNEL_TICKLESS,(16U), stk::SwitchStrategyFP32, stk::PlatformDefault >::OnRestoreWeight(), and stk::sync::Mutex::Unlock().

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GetHead()

DLHeadType * stk::util::DListEntry< ISyncObject, TClosedLoop >::GetHead ( )

inlineinherited

Get the list head this entry currently belongs to.

Returns

Pointer to the owning DListHead, or NULL if the entry is not linked.

Definition at line 85 of file stk_linked_list.h.

{ return m_head; }

GetNext()

DLEntryType * stk::util::DListEntry< ISyncObject, TClosedLoop >::GetNext ( )

inlineinherited

Get the next entry in the list.

Returns

Pointer to the next DListEntry, or NULL if this is the last entry (open list) or the first entry (closed loop, where next wraps to first).

Note

In a closed loop (TClosedLoop == true) this pointer is never NULL when the entry is linked.

Definition at line 98 of file stk_linked_list.h.

{ return m_next; }

GetPrev()

DLEntryType * stk::util::DListEntry< ISyncObject, TClosedLoop >::GetPrev ( )

inlineinherited

Get the previous entry in the list.

Returns

Pointer to the previous DListEntry, or NULL if this is the first entry (open list) or the last entry (closed loop, where prev wraps to last).

Note

In a closed loop (TClosedLoop == true) this pointer is never NULL when the entry is linked.

Definition at line 114 of file stk_linked_list.h.

{ return m_prev; }

GetTraceName()

const char * stk::ITraceable::GetTraceName ( ) const

inlineinherited

Get name.

Returns

Name string, or NULL if not set or if STK_SYNC_DEBUG_NAMES is 0.

Definition at line 416 of file stk_common.h.

    {
    #if STK_SYNC_DEBUG_NAMES
        return m_trace_name;
    #else
        return nullptr;
    #endif
    }

IsLinked()

bool stk::util::DListEntry< ISyncObject, TClosedLoop >::IsLinked ( ) const

inlineinherited

Check whether this entry is currently a member of any list.

Returns

true if linked (m_head != NULL); false otherwise.

Definition at line 127 of file stk_linked_list.h.

{ return (GetHead() != nullptr); }

Link()

void stk::util::DListEntry< ISyncObject, TClosedLoop >::Link ( DLHeadType * head, DLEntryType * next, DLEntryType * prev )

inlineprivateinherited

Wire this entry into a list between prev and next.

Parameters

[in]	head	The owning DListHead. Stored as a back-pointer for IsLinked() and ownership checks.
[in]	next	The entry that will follow this one, or NULL if this becomes the last entry.
[in]	prev	The entry that will precede this one, or NULL if this becomes the first entry.

Note

Called exclusively by DListHead::Link(). Assumes the entry is not currently linked. Updates the neighbours' forward/back pointers to splice this entry in.

Definition at line 162 of file stk_linked_list.h.

    {
        m_head = head;
        m_next = next;
        m_prev = prev;
 
        if (m_prev != nullptr)
        {
            m_prev->m_next = this;
        }
 
        if (m_next != nullptr)
        {
            m_next->m_prev = this;
        }
    }

NotifyAll()

void stk::sync::ConditionVariable::NotifyAll ( )

inline

Wake all waiting tasks.

Note

ISR-safe.

Definition at line 166 of file stk_sync_cv.h.

{
    const ScopedCriticalSection cs_;
    NotifyAll_CS(); // wakes all tasks in the wait list simultaneously
}

References NotifyAll_CS().

Referenced by stk_cv_notify_all().

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NotifyAll_CS()

void stk::sync::ConditionVariable::NotifyAll_CS ( )

inline

Wake all waiting tasks.

Warning

Caller must lock Critical Section or use ScopedCriticalSection prior calling this function.

Note

ISR-safe.

Definition at line 176 of file stk_sync_cv.h.

{
    WakeAll(); // wakes all tasks in the wait list simultaneously
}

References stk::ISyncObject::WakeAll().

Referenced by NotifyAll().

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NotifyOne()

void stk::sync::ConditionVariable::NotifyOne ( )

inline

Wake one waiting task.

Note

ISR-safe.

Definition at line 147 of file stk_sync_cv.h.

{
    const ScopedCriticalSection cs_;
    NotifyOne_CS();
}

References NotifyOne_CS().

Referenced by stk_cv_notify_one().

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NotifyOne_CS()

void stk::sync::ConditionVariable::NotifyOne_CS ( )

inline

Wake one waiting task.

Warning

Caller must lock Critical Section or use ScopedCriticalSection prior calling this function.

Note

ISR-safe.

Definition at line 157 of file stk_sync_cv.h.

{
    WakeOne(); // wakes the first task in the wait list (FIFO order), if any
}

References stk::ISyncObject::WakeOne().

Referenced by NotifyOne().

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operator const ISyncObject *()

stk::util::DListEntry< ISyncObject, TClosedLoop >::operator const ISyncObject * ( ) const

inlineinherited

Implicit conversion to a const pointer to the host object (T).

Note

Safe because T must derive from DListEntry<T, TClosedLoop>. Eliminates the need for explicit static_cast at call sites.

MISRA deviation: [STK-DEV-004] Rule 5-2-x.

Definition at line 141 of file stk_linked_list.h.

{ return static_cast<const T *>(this); }

operator ISyncObject *()

stk::util::DListEntry< ISyncObject, TClosedLoop >::operator ISyncObject* ( )

inlineinherited

Implicit conversion to a mutable pointer to the host object (T).

Note

Safe because T must derive from DListEntry<T, TClosedLoop>. Eliminates the need for explicit static_cast at call sites.

MISRA deviation: [STK-DEV-004] Rule 5-2-x.

Definition at line 134 of file stk_linked_list.h.

{ return static_cast<T *>(this); }

operator=()

ConditionVariable & stk::sync::ConditionVariable::operator= ( const ConditionVariable & )

privatedelete

RemoveWaitObject()

virtual void stk::ISyncObject::RemoveWaitObject ( IWaitObject * wobj )

inlinevirtualinherited

Called by kernel when a waiting task is being removed (timeout expired, wait aborted, task terminated etc.).

Parameters

[in]

wobj

Wait object to remove from the wait list.

Note

Must be called inside the critical section (see hw::CriticalSection, sync::ScopedCrticalSection).

Reimplemented in stk::sync::Event.

Definition at line 467 of file stk_common.h.

    {
        STK_ASSERT(wobj->GetHead() == &m_wait_list);
        m_wait_list.Unlink(wobj);
    }

References stk::util::DListEntry< T, TClosedLoop >::GetHead(), m_wait_list, and STK_ASSERT.

Referenced by stk::sync::Event::RemoveWaitObject().

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SetTraceName()

void stk::ITraceable::SetTraceName ( const char * name )

inlineinherited

Set name.

Parameters

[in]

name

Null-terminated string or NULL.

Note

If STK_SYNC_DEBUG_NAMES is 0 then calling this function has no effect.

Definition at line 404 of file stk_common.h.

    {
    #if STK_SYNC_DEBUG_NAMES
        m_trace_name = name;
    #else
        STK_UNUSED(name);
    #endif
    }

References STK_UNUSED.

Referenced by stk::memory::BlockMemoryPool::BlockMemoryPool(), and stk::memory::BlockMemoryPool::BlockMemoryPool().

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Tick()

bool stk::ISyncObject::Tick ( Timeout elapsed_ticks )

inlinevirtualinherited

Called by kernel on every system tick to handle timeout logic of waiting tasks.

Implementation of ISyncObject::Tick, see ISyncObject. Placed here as it depends on hw namespace.

Parameters

[in]

elapsed_ticks

Number of ticks elapsed between this and previous calls, in case of KERNEL_TICKLESS mode this value can be >1, for non-tickless mode it is always 1.

Returns

true if this synchronization object still has waiters with a finite timeout and requires further tick calls. false if the wait list is empty or all remaining waiters have infinite timeouts, signaling to the kernel that it may stop calling Tick() for this object until a new waiter is added.

Note

When this method returns false, the kernel unlinks this object from its active sync list. It will be re-linked automatically when the next waiter is added via AddWaitObject().

Does not need to be called inside critical section.

Definition at line 181 of file stk_helper.h.

{
    // note: ScopedCriticalSection usage
    //
    // Single-core: no critical section needed - Tick() runs inside the
    // SysTick ISR which already executes with interrupts disabled, making
    // re-entrancy impossible on the local core.
    //
    // Multi-core: critical section is required because the tick handler on
    // each core may call Tick() concurrently for the same Semaphore instance,
    // and ISyncObject::Tick() is not re-entrant.
#if (STK_ARCH_CPU_COUNT > 1)
    hw::CriticalSection::ScopedLock cs_;
#endif
 
    IWaitObject *itr = util::DListCast::ListEntryToParent<IWaitObject>(m_wait_list.GetFirst());
 
    while (itr != nullptr)
    {
        IWaitObject *const next = util::DListCast::ListEntryToParent<IWaitObject>(itr->GetNext());
 
        if (!itr->Tick(elapsed_ticks))
        {
            itr->Wake(true);
        }
 
        itr = next;
    }
 
    return !m_wait_list.IsEmpty();
}

References stk::util::DListEntry< T, TClosedLoop >::GetNext(), stk::util::DListCast::ListEntryToParent(), m_wait_list, stk::IWaitObject::Tick(), and stk::IWaitObject::Wake().

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Unlink()

void stk::util::DListEntry< ISyncObject, TClosedLoop >::Unlink ( )

inlineprivateinherited

Remove this entry from its current list.

Note

Called exclusively by DListHead::Unlink(). Patches the neighbours' pointers to bridge over this entry, then clears m_head, m_next, and m_prev to NULL so the entry is in a clean unlinked state.

Does not update DListHead::m_count or m_first / m_last — those are the responsibility of the calling DListHead::Unlink().

Definition at line 186 of file stk_linked_list.h.

    {
        if (m_prev != nullptr)
        {
            m_prev->m_next = m_next;
        }
 
        if (m_next != nullptr)
        {
            m_next->m_prev = m_prev;
        }
 
        m_head = nullptr;
        m_next = nullptr;
        m_prev = nullptr;
    }

Wait()

bool stk::sync::ConditionVariable::Wait ( IMutex & mutex, Timeout timeout_ticks = WAIT_INFINITE )

inline

Wait for a signal.

Atomically releases mutex and blocks the calling task. The mutex is re-acquired before the function returns, regardless of whether the wake was caused by a signal or a timeout.

Parameters

[in]	mutex	An IMutex-compatible lock that must be held by the calling task before Wait() is called. The kernel releases it atomically during suspension and re-acquires it on wake.
[in]	timeout_ticks	Maximum time to wait (ticks). Use WAIT_INFINITE to block indefinitely, NO_WAIT to return immediately without blocking.

Returns

true if signaled, false if timeout occurred or NO_WAIT was passed.

Warning

ISR-safe only with timeout_ticks=NO_WAIT, ISR-unsafe otherwise.

Definition at line 127 of file stk_sync_cv.h.

{
    // API contract: mutex must be locked by the calling task before Wait() is called.
    // The kernel releases it atomically during suspension and re-acquires it on wake.
    bool success = false;
 
    if (timeout_ticks != NO_WAIT)
    {
        STK_ASSERT(!hw::IsInsideISR()); // API contract: caller must not be in ISR if timeout_ticks!=NO_WAIT
        
        success = !IKernelService::GetInstance()->Wait(this, &mutex, timeout_ticks)->IsTimeout();
    }
 
    return success;
}

References stk::IKernelService::GetInstance(), stk::hw::IsInsideISR(), stk::IWaitObject::IsTimeout(), stk::NO_WAIT, STK_ASSERT, and stk::IKernelService::Wait().

Referenced by osThreadJoin(), and stk_cv_wait().

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WakeAll()

void stk::ISyncObject::WakeAll ( )

inlineprotectedinherited

Wake all tasks currently in the wait list.

Note

Each woken task is notified with timeout=false, indicating a successful signal (not a timeout expiry).

Does nothing if no tasks are currently waiting.

Must be called inside the critical section (see hw::CriticalSection, sync::ScopedCrticalSection).

Definition at line 526 of file stk_common.h.

    {
        while (IWaitObject *const obj = util::DListCast::ListEntryToParent<IWaitObject>(m_wait_list.GetFirst()))
        {
            obj->Wake(false);
        }
    }

References stk::util::DListCast::ListEntryToParent(), and m_wait_list.

Referenced by stk::sync::ConditionVariable::NotifyAll_CS(), stk::sync::Event::Pulse(), and stk::sync::Event::Set().

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WakeOne()

void stk::ISyncObject::WakeOne ( )

inlineprotectedinherited

Wake the first task in the wait list (FIFO order).

Note

The woken task is notified with timeout=false, indicating a successful signal (not a timeout expiry).

Does nothing if no tasks are currently waiting.

Must be called inside the critical section (see hw::CriticalSection, sync::ScopedCrticalSection).

Definition at line 512 of file stk_common.h.

    {      
        if (IWaitObject *const obj = util::DListCast::ListEntryToParent<IWaitObject>(m_wait_list.GetFirst()))
        {
            obj->Wake(false);
        }
    }

References stk::util::DListCast::ListEntryToParent(), and m_wait_list.

Referenced by stk::sync::ConditionVariable::NotifyOne_CS(), stk::sync::Event::Pulse(), stk::sync::Event::Set(), and stk::sync::Semaphore::Signal().

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Member Data Documentation

m_head

DLHeadType* stk::util::DListEntry< ISyncObject, TClosedLoop >::m_head

privateinherited

Owning list head, or NULL when the entry is not linked.

Definition at line 203 of file stk_linked_list.h.

m_next

DLEntryType* stk::util::DListEntry< ISyncObject, TClosedLoop >::m_next

privateinherited

Next entry in the list, or NULL (open list boundary) / first entry (closed loop).

Definition at line 204 of file stk_linked_list.h.

m_prev

DLEntryType* stk::util::DListEntry< ISyncObject, TClosedLoop >::m_prev

privateinherited

Previous entry in the list, or NULL (open list boundary) / last entry (closed loop).

Definition at line 205 of file stk_linked_list.h.

m_wait_list

IWaitObject::ListHeadType stk::ISyncObject::m_wait_list

protectedinherited

tasks blocked on this object

Definition at line 534 of file stk_common.h.

Referenced by AddWaitObject(), FindWeightHigherThan(), ISyncObject(), stk::sync::Event::Pulse(), RemoveWaitObject(), stk::sync::Semaphore::Signal(), Tick(), stk::sync::Mutex::Unlock(), WakeAll(), WakeOne(), stk::sync::ConditionVariable::~ConditionVariable(), stk::sync::Event::~Event(), stk::sync::Mutex::~Mutex(), and stk::sync::Semaphore::~Semaphore().

---

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

• stk_sync_cv.h