stk_sync_barrier.h

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/*
 * SuperTinyKernel(TM) RTOS: Lightweight High-Performance Deterministic C++ RTOS for Embedded Systems.
 *
 * Source: https://github.com/SuperTinyKernel-RTOS
 *
 * Copyright (c) 2022-2026 Neutron Code Limited <stk@neutroncode.com>. All Rights Reserved.
 * License: MIT License, see LICENSE for a full text.
 */
 
#ifndef STK_SYNC_BARRIER_H_
#define STK_SYNC_BARRIER_H_
 
#include "stk_sync_mutex.h"
#include "stk_sync_cv.h"

 
namespace stk {
namespace sync {

class Barrier final : public ITraceable
{
public:
    explicit Barrier(uint32_t count) : m_threshold(count), m_count(count), m_generation(0U)
    {
        STK_ASSERT(count != 0U); // API contract: number of parties cannot be 0
    }

    STK_VIRT_DTOR ~Barrier()
    {}

    bool Wait();

    uint32_t GetThreshold() const { return m_threshold; }
 
private:
    STK_NONCOPYABLE_CLASS(Barrier);
 
    Mutex             m_mutex;      
    ConditionVariable m_cond;       
    const uint32_t    m_threshold;  
    uint32_t          m_count;      
    uint32_t          m_generation; 
};
 
// ---------------------------------------------------------------------------
// Wait
// ---------------------------------------------------------------------------
 
inline bool Barrier::Wait()
{
    bool is_last = false;
 
    STK_ASSERT(!hw::IsInsideISR()); // API contract: caller must not be in ISR
 
    m_mutex.Lock();
 
    const uint32_t gen = m_generation;
 
    if (--m_count == 0U)
    {
        // last task to arrive: start a new generation and release everyone else
        ++m_generation;
        m_count = m_threshold;
 
        m_cond.NotifyAll();
 
        is_last = true;
    }
    else
    {
        // wait in a loop to guard against spurious wakeups: keep waiting while
        // we are still in the same generation we entered with
        while (gen == m_generation)
        {
            STK_UNUSED(m_cond.Wait(m_mutex, WAIT_INFINITE));
        }
    }
 
    m_mutex.Unlock();
 
    return is_last;
}
 
} // namespace sync
} // namespace stk
 
#endif /* STK_SYNC_BARRIER_H_ */