stk::sync::Semaphore Class Reference

Counting semaphore primitive for resource management and signaling. More...

#include <stk_sync_semaphore.h>

Inheritance diagram for stk::sync::Semaphore:

Collaboration diagram for stk::sync::Semaphore:

Public 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.

Public Member Functions
	Semaphore (uint16_t initial_count=0U, uint16_t max_count=COUNT_MAX)
	Constructor.
	~Semaphore ()
	Destructor.
EWaitResult	WaitEx (Timeout timeout_ticks=WAIT_INFINITE)
	Wait for a signal (decrement counter), preserving the full wait outcome.
bool	Wait (Timeout timeout_ticks=WAIT_INFINITE)
	Wait for a signal (decrement counter).
bool	TryWait ()
	Poll the semaphore without blocking (decrement counter if available).
void	Signal ()
	Post a signal (increment counter).
bool	TrySignal ()
	Try to post a signal without exceeding max_count.
uint16_t	GetCount () const
	Get current counter value.
void	AddWaitObject (IWaitObject *wobj) override
	Called by kernel when a new task starts waiting on this event.
void	RemoveWaitObject (IWaitObject *wobj) override
	Called by kernel when a waiting task is being removed (timeout expired, wait aborted, task terminated etc.).
const IWaitObject::ListHeadType &	GetWaitList () const override
	Get list of tasks blocked on this object.
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.
TId	GetFirstWaiterTid () const
	Get id of the task which is first in the wait list (FIFO order), i.e. the one that WakeOne() would wake next.
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	SetTraceName (const char *name)
	Set name.
const char *	GetTraceName () const
	Get name.

Static Public Member Functions
static void	AddWaitObject (IWaitObject::ListHeadType &wlist, IWaitObject *wobj)
	Called by kernel when a new task starts waiting on this event.
static void	RemoveWaitObject (IWaitObject::ListHeadType &wlist, IWaitObject *wobj)
	Called by kernel when a waiting task is being removed (timeout expired, wait aborted, task terminated etc.).
static void	WakeOne (IWaitObject::ListHeadType &wlist)
	Wake the first task in the wait list (FIFO order).
static void	WakeAll (IWaitObject::ListHeadType &wlist)
	Wake all tasks currently in the wait list.

Static Public Attributes
static const uint16_t	COUNT_MAX = 0xFFFEU
	Max count value supported.

Protected Member Functions
void	WakeOne () override
	Wake the first task in the wait list (FIFO order).
void	WakeAll () override
	Wake all tasks currently in the wait list.
IWaitObject::ListHeadType &	GetMutableWaitList () override
	Get list of tasks blocked on this object.

Protected Attributes
IWaitObject::ListHeadType	m_wait_list
	Tasks blocked on this object.

Private Member Functions
	Semaphore (const Semaphore &)=delete
Semaphore &	operator= (const Semaphore &)=delete
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
uint16_t	m_count
	Internal resource counter.
uint16_t	m_count_max
	Counter max limit.
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

Counting semaphore primitive for resource management and signaling.

Counting semaphore maintains an internal counter to manage access to a limited number of resources. Unlike a Condition Variable, a Semaphore is stateful: if Signal() is called when no tasks are waiting, the signal is "remembered" by incrementing the internal counter.

Note

This implementation uses a Direct Handover policy: when a task is waiting, Signal() gives the resource "token" directly to the first task in the wait list without incrementing the counter. The waking task is then guaranteed ownership of that token upon returning from Wait().

// Example: Resource throttling
// Initialize with 3 permits (e.g., max 3 concurrent tasks accessing the same resource)
stk::sync::Semaphore g_Limiter(3);
 
void Worker() {
    // attempt to acquire a permit with a 1000 tick timeout
    if (g_Limiter.Wait(1000)) {
 
        // ... access limited resource ...
 
        // release the permit back to the semaphore
        g_Limiter.Signal();
    }
}

See also

ISyncObject, IWaitObject, IKernelService::Wait

Note

Only available when kernel is compiled with KERNEL_SYNC mode enabled.

Examples

D:/SVN/private/stk/interop/c/include/stk_c.h.

Definition at line 55 of file stk_sync_semaphore.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 625 of file stk_common.h.

ListHeadType

typedef DLHeadType stk::ISyncObject::ListHeadType

inherited

List head type for ISyncObject elements.

Definition at line 620 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

Semaphore() [1/2]

stk::sync::Semaphore::Semaphore ( uint16_t initial_count = 0U, uint16_t max_count = COUNT_MAX )

inlineexplicit

Constructor.

Initializes the semaphore with a specific count and maximum limit. Setting initial_count to a non-zero value allows for immediate resource acquisition.

Parameters

[in]	initial_count	Starting value of the internal counter (available permits).
[in]	max_count	Maximum value the counter is allowed to reach.

Precondition

initial_count <= max_count.

Note

Triggers an assertion in a debug build if initial_count exceeds max_count.

Definition at line 71 of file stk_sync_semaphore.h.

        : m_count(initial_count), m_count_max(max_count)
    {
        STK_ASSERT(initial_count <= max_count); // API contract: initial count must not exceed maximum
    }

References COUNT_MAX, m_count, m_count_max, and STK_ASSERT.

Referenced by operator=().

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~Semaphore()

stk::sync::Semaphore::~Semaphore ( )

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 83 of file stk_sync_semaphore.h.

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

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

Referenced by tx_semaphore_delete().

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Semaphore() [2/2]

stk::sync::Semaphore::Semaphore ( const Semaphore & )

privatedelete

Member Function Documentation

AddWaitObject() [1/2]

void stk::ISyncObject::AddWaitObject ( IWaitObject::ListHeadType & wlist, IWaitObject * wobj )

inlinestaticinherited

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

Parameters

[in]

wobj

Wait object representing blocked task.

Note

Utility for AddWaitObject and ARM TrustZone support.

Definition at line 631 of file stk_common.h.

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

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

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

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AddWaitObject() [2/2]

void stk::SyncObjectBase::AddWaitObject ( IWaitObject * wobj )

inlineoverridevirtualinherited

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).

Implements stk::ISyncObject.

Definition at line 256 of file stk_helper.h.

    {
        ISyncObject::AddWaitObject(m_wait_list, wobj);
    }

References stk::ISyncObject::AddWaitObject(), and m_wait_list.

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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 351 of file stk_helper.h.

{
    Weight max_weight = NO_WEIGHT;
    const IWaitObject *itr = util::DListCast::ListEntryToParent<const IWaitObject>(GetWaitList().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(), GetWaitList(), stk::ITask::GetWeight(), stk::util::DListCast::ListEntryToParent(), and stk::NO_WEIGHT.

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

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GetCount()

uint16_t stk::sync::Semaphore::GetCount ( ) const

inline

Get current counter value.

Returns

Advisory snapshot of the counter. May be stale by the time the caller acts on it. Atomic on 32-bit aligned targets.

Note

ISR-safe on targets where a 32-bit aligned read is a single instruction (all supported STK architectures). Not safe for read-modify-write use.

Definition at line 146 of file stk_sync_semaphore.h.

{ return m_count; }

References m_count.

Referenced by osSemaphoreGetCount(), stk_sem_get_count(), tx_semaphore_ceiling_put(), tx_semaphore_info_get(), uxSemaphoreGetCount(), xQueueAddToSet(), xQueueRemoveFromSet(), xSemaphoreGive(), xSemaphoreGiveFromISR(), and xTaskNotifyStateClearIndexed().

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GetFirstWaiterTid()

TId stk::ISyncObject::GetFirstWaiterTid ( ) const

inlineinherited

Get id of the task which is first in the wait list (FIFO order), i.e. the one that WakeOne() would wake next.

Returns

TId of the first waiter, or TID_NONE if no tasks are currently waiting.

Note

Read-only introspection for diagnostics / telemetry.

The result is a snapshot: call inside the critical section (see hw::CriticalSection, sync::ScopedCrticalSection) if the list may change concurrently.

See also

GetWaitList

Definition at line 726 of file stk_common.h.

    {
        const IWaitObject *const obj = util::DListCast::ListEntryToParent<const IWaitObject>(
                GetWaitList().GetFirst());
 
        return ((obj != nullptr) ? obj->GetTid() : TID_NONE);
    }

References stk::IWaitObject::GetTid(), GetWaitList(), stk::util::DListCast::ListEntryToParent(), and stk::TID_NONE.

Referenced by anonymous_namespace{threadx_stk.cpp}::FillSuspended().

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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; }

Referenced by stk::SyncObjectBase::~SyncObjectBase().

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GetMutableWaitList()

IWaitObject::ListHeadType & stk::SyncObjectBase::GetMutableWaitList ( )

inlineoverrideprotectedvirtualinherited

Get list of tasks blocked on this object.

Implements stk::ISyncObject.

Definition at line 307 of file stk_helper.h.

    {
        return m_wait_list;
    }

References m_wait_list.

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 582 of file stk_common.h.

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

GetWaitList()

const IWaitObject::ListHeadType & stk::SyncObjectBase::GetWaitList ( ) const

inlineoverridevirtualinherited

Get list of tasks blocked on this object.

Note

Read-only access for diagnostics / telemetry.

The result is a snapshot: call inside the critical section (see hw::CriticalSection, sync::ScopedCrticalSection) if the list may change concurrently.

Implements stk::ISyncObject.

Definition at line 266 of file stk_helper.h.

    {
        return m_wait_list;
    }

References m_wait_list.

Referenced by tx_semaphore_ceiling_put().

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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;
        }
    }

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=()

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

privatedelete

References Semaphore().

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RemoveWaitObject() [1/2]

void stk::ISyncObject::RemoveWaitObject ( IWaitObject::ListHeadType & wlist, IWaitObject * wobj )

inlinestaticinherited

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

Utility for AddWaitObject and ARM TrustZone support.

Definition at line 647 of file stk_common.h.

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

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

Referenced by stk::SyncObjectBase::RemoveWaitObject().

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RemoveWaitObject() [2/2]

void stk::SyncObjectBase::RemoveWaitObject ( IWaitObject * wobj )

inlineoverridevirtualinherited

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).

Implements stk::ISyncObject.

Definition at line 261 of file stk_helper.h.

    {
        ISyncObject::RemoveWaitObject(m_wait_list, wobj);
    }

References m_wait_list, and stk::ISyncObject::RemoveWaitObject().

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 570 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(), stk::memory::BlockMemoryPool::BlockMemoryPool(), stk::memory::BytePool::BytePool(), stk::memory::BytePool::BytePool(), tx_block_pool_create(), tx_event_flags_create(), tx_mutex_create(), tx_queue_create(), and tx_semaphore_create().

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Signal()

void stk::sync::Semaphore::Signal ( )

inline

Post a signal (increment counter).

Note

Gives "token" directly to the waking task. The count is not incremented, and the waking task does not decrement it.

ISR-safe.

Warning

API contract: the counter must not already be at max_count with no task waiting. Violating this triggers an assertion in a debug build. Use TrySignal() instead if a signal that would exceed max_count should be tolerated (e.g. a redundant post) rather than treated as a caller error.

Definition at line 195 of file stk_sync_semaphore.h.

{
    const bool success = TrySignal();
    STK_UNUSED(success);
    STK_ASSERT(success); // API contract: the count must not exceed maximum
}

References STK_ASSERT, STK_UNUSED, and TrySignal().

Referenced by stk_sem_signal(), xSemaphoreGive(), xSemaphoreGiveFromISR(), xTaskNotifyAndQueryIndexed(), xTaskNotifyGiveIndexed(), and xTaskNotifyIndexed().

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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 316 of file stk_helper.h.

{
    IWaitObject::ListHeadType &wlist = GetMutableWaitList();
 
    // 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)
    const hw::CriticalSection::ScopedLock cs_;
#endif
 
    IWaitObject *itr = util::DListCast::ListEntryToParent<IWaitObject>(wlist.GetFirst());
 
    while (itr != nullptr)
    {
        IWaitObject *const next = util::DListCast::ListEntryToParent<IWaitObject>(itr->GetNext());
 
        if (!itr->Tick(elapsed_ticks))
        {
            itr->Wake(true);
        }
 
        itr = next;
    }
 
    return !wlist.IsEmpty();
}

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

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TrySignal()

bool stk::sync::Semaphore::TrySignal ( )

inline

Try to post a signal without exceeding max_count.

Identical to Signal(), except that if the counter is already at max_count and no task is waiting, this returns false instead of asserting. The check and the increment (or hand-off to a waiter) happen atomically under the same critical section, so this is safe to call from multiple concurrent signalers without racing each other the way a separate GetCount() check followed by Signal() would.

Note

ISR-safe.

Returns

true if signaled (incremented, or handed directly to a waiter), false if the counter was already at max_count and nobody was waiting.

Definition at line 206 of file stk_sync_semaphore.h.

{
    const ScopedCriticalSection cs_;
    bool success = true;
 
    if (m_wait_list.IsEmpty())
    {
        if (m_count >= m_count_max)
        {
            // counter already saturated and no one is waiting to hand the token to directly
            success = false;
        }
        else
        {
            // no one is waiting, save signal for later
            m_count = static_cast<uint16_t>(m_count + 1U);
            __stk_full_memfence();
        }
    }
    else
    {
        // give signal directly to the first waiting task
        WakeOne();
    }
 
    return success;
}

References m_count, m_count_max, stk::SyncObjectBase::m_wait_list, and stk::SyncObjectBase::WakeOne().

Referenced by Signal(), stk_sem_trysignal(), and tx_semaphore_ceiling_put().

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TryWait()

bool stk::sync::Semaphore::TryWait ( )

inline

Poll the semaphore without blocking (decrement counter if available).

Checks if a resource token is available. If so, decrements the counter and returns immediately without yielding the CPU or touching the kernel wait list. If the counter is zero, returns immediately with false.

Note

ISR-safe.

Returns

true if a resource token was acquired, false if count was zero.

Definition at line 114 of file stk_sync_semaphore.h.

{ return Wait(NO_WAIT); }

References stk::NO_WAIT, and Wait().

Referenced by stk_sem_trywait(), xSemaphoreTakeFromISR(), and xTaskNotifyStateClearIndexed().

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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::Semaphore::Wait ( Timeout timeout_ticks = WAIT_INFINITE )

inline

Wait for a signal (decrement counter).

Parameters

[in]

timeout_ticks

Maximum time to wait (ticks).

Warning

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

Returns

True if acquired, false otherwise (timeout, cancellation or NO_WAIT with no token available). Use WaitEx() to tell these apart.

Definition at line 105 of file stk_sync_semaphore.h.

{ return (WaitEx(timeout_ticks) == WAIT_RESULT_SIGNAL); }

References stk::WAIT_INFINITE, stk::WAIT_RESULT_SIGNAL, and WaitEx().

Referenced by stk_sem_wait(), TryWait(), ulTaskNotifyTakeIndexed(), xSemaphoreTake(), and xTaskNotifyWaitIndexed().

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WaitEx()

EWaitResult stk::sync::Semaphore::WaitEx ( Timeout timeout_ticks = WAIT_INFINITE )

inline

Wait for a signal (decrement counter), preserving the full wait outcome.

Parameters

[in]

timeout_ticks

Maximum time to wait (ticks).

Warning

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

Returns

WAIT_RESULT_SIGNAL if a token was acquired, WAIT_RESULT_TIMEOUT if no token was available and the timeout expired (or NO_WAIT was passed), WAIT_RESULT_CANCELED if the wait was cancelled via IKernel::CancelTaskWait(), WAIT_RESULT_FAIL if the kernel rejected the wait. A non-signal result never consumes a token.

Definition at line 159 of file stk_sync_semaphore.h.

{
    ScopedCriticalSection cs_;
 
    // NO_WAIT with no token available is reported as an immediately-expired timeout
    EWaitResult result = WAIT_RESULT_TIMEOUT;
 
    // fast path: resource is available
    if (m_count != 0U)
    {
        m_count = static_cast<uint16_t>(m_count - 1U);
        __stk_full_memfence();
        result = WAIT_RESULT_SIGNAL;
    }
    // slow path: block until Signal() or timeout
    else if (timeout_ticks != NO_WAIT)
    {
        STK_ASSERT(!hw::IsInsideISR()); // API contract: caller must not be in ISR if timeout_ticks!=NO_WAIT
 
        // note: after waking, if not a timeout, we effectively own the resource that Signal() produced
        // but didn't put into m_count (see logic of if (m_wait_list.IsEmpty()) in Signal())
        result = IKernelService::GetInstance()->Wait(this, &cs_, timeout_ticks);
    }
    // try lock behavior (timeout_ticks=NO_WAIT)
    else
    {
        // result is WAIT_RESULT_TIMEOUT already, noop
    }
 
    return result;
}

References stk::IKernelService::GetInstance(), stk::hw::IsInsideISR(), m_count, stk::NO_WAIT, STK_ASSERT, stk::IKernelService::Wait(), stk::WAIT_RESULT_SIGNAL, and stk::WAIT_RESULT_TIMEOUT.

Referenced by osSemaphoreAcquire(), stk_sem_wait_ex(), and Wait().

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WakeAll() [1/2]

void stk::ISyncObject::WakeAll ( IWaitObject::ListHeadType & wlist )

inlinestaticinherited

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.

Utility for AddWaitObject and ARM TrustZone support.

Definition at line 701 of file stk_common.h.

    {
        for (IWaitObject *obj = util::DListCast::ListEntryToParent<IWaitObject>(wlist.GetFirst());
             obj != nullptr;
             obj = util::DListCast::ListEntryToParent<IWaitObject>(wlist.GetFirst()))
        {
            obj->Wake(false);
        }
    }

References stk::util::DListHead< T, TClosedLoop >::GetFirst(), and stk::util::DListCast::ListEntryToParent().

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WakeAll() [2/2]

void stk::SyncObjectBase::WakeAll ( )

inlineoverrideprotectedvirtualinherited

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).

Implements stk::ISyncObject.

Definition at line 302 of file stk_helper.h.

    {
        IKernelService::GetInstance()->Wake(this, true);
    }

References stk::IKernelService::GetInstance(), and stk::IKernelService::Wake().

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

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WakeOne() [1/2]

void stk::ISyncObject::WakeOne ( IWaitObject::ListHeadType & wlist )

inlinestaticinherited

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.

Utility for AddWaitObject and ARM TrustZone support.

Definition at line 686 of file stk_common.h.

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

References stk::util::DListHead< T, TClosedLoop >::GetFirst(), stk::util::DListCast::ListEntryToParent(), and stk::IWaitObject::Wake().

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WakeOne() [2/2]

void stk::SyncObjectBase::WakeOne ( )

inlineoverrideprotectedvirtualinherited

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).

Implements stk::ISyncObject.

Definition at line 297 of file stk_helper.h.

    {
        IKernelService::GetInstance()->Wake(this, false);
    }

References stk::IKernelService::GetInstance(), and stk::IKernelService::Wake().

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

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Member Data Documentation

COUNT_MAX

const uint16_t stk::sync::Semaphore::COUNT_MAX = 0xFFFEU

static

Max count value supported.

Definition at line 60 of file stk_sync_semaphore.h.

Referenced by osSemaphoreNew(), Semaphore(), stk_sem_create(), tx_semaphore_create(), xSemaphoreCreateCounting(), xSemaphoreCreateCountingStatic(), xSemaphoreGive(), and xSemaphoreGiveFromISR().

m_count

uint16_t stk::sync::Semaphore::m_count

private

Internal resource counter.

Definition at line 151 of file stk_sync_semaphore.h.

Referenced by GetCount(), Semaphore(), TrySignal(), and WaitEx().

m_count_max

uint16_t stk::sync::Semaphore::m_count_max

private

Counter max limit.

Definition at line 152 of file stk_sync_semaphore.h.

Referenced by Semaphore(), and TrySignal().

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::SyncObjectBase::m_wait_list

protectedinherited

Tasks blocked on this object.

Definition at line 312 of file stk_helper.h.

Referenced by AddWaitObject(), GetMutableWaitList(), GetWaitList(), stk::sync::Event::Pulse(), RemoveWaitObject(), SyncObjectBase(), stk::sync::Semaphore::TrySignal(), stk::sync::FastMutex::Unlock(), stk::sync::Mutex::Unlock(), stk::sync::ConditionVariable::~ConditionVariable(), stk::sync::Event::~Event(), stk::sync::FastMutex::~FastMutex(), stk::sync::Mutex::~Mutex(), and stk::sync::Semaphore::~Semaphore().

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

• stk_sync_semaphore.h