mutex.cxx

ecos为实时嵌入式操作系统

    // Unlock the scheduler and maybe switch threads
    Cyg_Scheduler::unlock();

    CYG_REPORT_RETURN();
}

//==========================================================================
// Condition variables

Cyg_Condition_Variable::Cyg_Condition_Variable(
    Cyg_Mutex   &mx                // linked mutex
    )
{
    CYG_REPORT_FUNCTION();
        
    mutex       = &mx;

    CYG_ASSERTCLASS( mutex, "Invalid mutex argument");

    CYG_REPORT_RETURN();
}

// -------------------------------------------------------------------------
// Destructor

Cyg_Condition_Variable::~Cyg_Condition_Variable()
{
    CYG_REPORT_FUNCTION();
        
    CYG_ASSERT( queue.empty(), "Deleting condvar with waiting threads");

    CYG_REPORT_RETURN();
}

// -------------------------------------------------------------------------

#ifdef CYGDBG_USE_ASSERTS

bool
Cyg_Condition_Variable::check_this( cyg_assert_class_zeal zeal) const
{
    bool result = true;

    CYG_REPORT_FUNCTYPE("returning %d");
    CYG_REPORT_FUNCARG1("zeal = %d", zeal);
        
    // check that we have a non-NULL pointer first
    if( this == NULL )
        result = false;
    else {
        
        switch( zeal )
        {
        case cyg_system_test:
        case cyg_extreme:
        case cyg_thorough:
            if( !mutex->check_this(zeal) )
                result = false;
        case cyg_quick:
        case cyg_trivial:
        case cyg_none:
        default:
            break;
        }
    }

    CYG_REPORT_RETVAL(result);
    return result;
}

#endif

// -------------------------------------------------------------------------
// Wait for condition to be true    
// Note: if this function is entered with the scheduler locked (e.g. to
// suspend DSR processing) then there is no need to take the lock.  Also
// in this case, exit with the scheduler locked, which allows this function
// to be used in a totally thread-safe manner.

void
Cyg_Condition_Variable::wait(void)
{
    CYG_REPORT_FUNCTION();
        
    Cyg_Thread *self = Cyg_Thread::self();

    cyg_int32 current_lock = Cyg_Scheduler::get_sched_lock();

    if (current_lock == 0) 
        // Prevent preemption
        Cyg_Scheduler::lock();

    CYG_ASSERTCLASS( this, "Bad this pointer");
    CYG_ASSERTCLASS( mutex, "Corrupt mutex");
    CYG_ASSERTCLASS( self, "Bad self thread");

    CYG_INSTRUMENT_CONDVAR(WAIT, this, 0);
    
    mutex->unlock();

    self->set_sleep_reason( Cyg_Thread::WAIT );
        
    self->sleep();
        
    queue.enqueue( self );

    CYG_ASSERT( Cyg_Scheduler::get_sched_lock() == 1, "Called with non-zero scheduler lock");
    
    // Unlock the scheduler and switch threads
    Cyg_Scheduler::unlock();

    CYG_INSTRUMENT_CONDVAR(WOKE, this, self->get_wake_reason());
    
    CYG_ASSERTCLASS( this, "Bad this pointer");
    CYG_ASSERTCLASS( mutex, "Corrupt mutex");

    switch( self->get_wake_reason() )
    {
    case Cyg_Thread::EXIT:            
        self->exit();
        break;

    default:
        break;
    }


    // When we awake, we must re-acquire the mutex.  Note that while
    // it is essential to release the mutex and queue on the CV
    // atomically relative to other threads, to avoid races, it is not
    // necessary for us to re-acquire the mutex in the same atomic
    // action. Hence we can do it after unlocking the scheduler.
    // We need to loop here in case the thread is released while waiting
    // for the mutex. It is essential that we exit this function with the
    // mutex claimed.
    
    while ( !mutex->lock() )
        continue;

    CYG_ASSERTCLASS( this, "Bad this pointer");
    CYG_ASSERTCLASS( mutex, "Corrupt mutex");
    CYG_ASSERT( mutex->owner == self, "Not mutex owner");

    CYG_REPORT_RETURN();

    if (current_lock)
        // Reacquire the DSR pseudo lock
        Cyg_Scheduler::lock();
}

// -------------------------------------------------------------------------
// Wake one thread

void
Cyg_Condition_Variable::signal(void)
{
    CYG_REPORT_FUNCTION();
        
    CYG_ASSERTCLASS( this, "Bad this pointer");
    CYG_ASSERTCLASS( mutex, "Corrupt mutex");

    // Prevent preemption
    Cyg_Scheduler::lock();

    CYG_INSTRUMENT_CONDVAR(SIGNAL, this, 0);
    
    if( !queue.empty() )
    {
        // The queue is non-empty, so grab the next
        // thread from it and wake it up.

        Cyg_Thread *thread = queue.dequeue();

        CYG_ASSERTCLASS( thread, "Bad thread pointer");
        
        thread->set_wake_reason( Cyg_Thread::DONE );
        
        thread->wake();

        CYG_INSTRUMENT_CONDVAR(WAKE, this, thread);
        
    }
    
    CYG_ASSERTCLASS( this, "Bad this pointer");
    CYG_ASSERTCLASS( mutex, "Corrupt mutex");

    // Unlock the scheduler and maybe switch threads
    Cyg_Scheduler::unlock();

    CYG_REPORT_RETURN();
}

// -------------------------------------------------------------------------
// Set cond true, wake all threads

void
Cyg_Condition_Variable::broadcast(void)
{
    CYG_REPORT_FUNCTION();
        
    CYG_ASSERTCLASS( this, "Bad this pointer");
    CYG_ASSERTCLASS( mutex, "Corrupt mutex");

    // Prevent preemption
    Cyg_Scheduler::lock();

    CYG_INSTRUMENT_CONDVAR(BROADCAST, this, 0);
    
    // Grab all the threads from the queue and let them
    // go.
    
    while( !queue.empty() )
    {
        Cyg_Thread *thread = queue.dequeue();

        CYG_ASSERTCLASS( thread, "Bad thread pointer");
        
        thread->set_wake_reason( Cyg_Thread::DONE );
        
        thread->wake();

        CYG_INSTRUMENT_CONDVAR(WAKE, this, thread);        
    }
    
    CYG_ASSERTCLASS( this, "Bad this pointer");
    CYG_ASSERTCLASS( mutex, "Corrupt mutex");
    
    // Unlock the scheduler and maybe switch threads
    Cyg_Scheduler::unlock();    

    CYG_REPORT_RETURN();
}

// -------------------------------------------------------------------------
// Optional timed wait on a CV

#if defined(CYGMFN_KERNEL_SYNCH_CONDVAR_TIMED_WAIT)

cyg_bool
Cyg_Condition_Variable::wait( cyg_tick_count timeout )
{
    CYG_REPORT_FUNCTYPE("returning %d");
    CYG_REPORT_FUNCARG1("timeout = %d", timeout);
        
    CYG_ASSERTCLASS( this, "Bad this pointer");
    CYG_ASSERTCLASS( mutex, "Corrupt mutex");

    cyg_bool result = true;
    
    Cyg_Thread *self = Cyg_Thread::self();

    CYG_ASSERTCLASS( self, "Bad self thread");
    
    // Prevent preemption
    Cyg_Scheduler::lock();

    CYG_INSTRUMENT_CONDVAR(TIMED_WAIT, this, 0 );
    
    mutex->unlock();

    // The ordering of sleep() and set_timer() here are
    // important. If the timeout is in the past, the thread
    // will be woken up immediately and will not sleep.
    
    self->sleep();
        
    // Set the timer and sleep reason
    self->set_timer( timeout, Cyg_Thread::TIMEOUT );

    // Only enqueue if the timeout has not already fired.
    if( self->get_wake_reason() == Cyg_Thread::NONE )
        queue.enqueue( self );

    CYG_ASSERT( Cyg_Scheduler::get_sched_lock() == 1, "Called with non-zero scheduler lock");
    
    // Unlock the scheduler and switch threads
    Cyg_Scheduler::unlock();

    CYG_ASSERTCLASS( this, "Bad this pointer");
    CYG_ASSERTCLASS( mutex, "Corrupt mutex");
    
    self->clear_timer();

    CYG_INSTRUMENT_CONDVAR(WOKE, this, self->get_wake_reason());
    
    switch( self->get_wake_reason() )
    {
    case Cyg_Thread::TIMEOUT:            
    case Cyg_Thread::DESTRUCT:          // which, the cv or the mutex?
    case Cyg_Thread::BREAK:
        result = false;
        break;
            
    case Cyg_Thread::EXIT:            
        self->exit();
        break;

    default:
        break;
    }

    
    // When we awake, we must re-acquire the mutex.  Note that while
    // it is essential to release the mutex and queue on the CV
    // atomically relative to other threads, to avoid races, it is not
    // necessary for us to re-acquire the mutex in the same atomic
    // action. Hence we can do it after unlocking the scheduler.

    // FIXME: what if we woke up above due to TIMEOUT/DESTRUCT/BREAK?
    // In that situation is it correct to not lock the mutex?
    if (false != result)
        result = mutex->lock();

    CYG_ASSERTCLASS( this, "Bad this pointer");
    CYG_ASSERTCLASS( mutex, "Corrupt mutex");

    CYG_REPORT_RETVAL(result);
    
    return result;
}

#endif


// -------------------------------------------------------------------------
// EOF sync/mutex.cxx