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//==========================================================================

//

//      sync/cnt_sem.cxx

//

//      Counting semaphore implementation

//

//==========================================================================

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//==========================================================================

//#####DESCRIPTIONBEGIN####

//

// Author(s):   nickg

// Contributors:        nickg

// Date:        1997-09-24

// Purpose:     Cyg_Counting_Semaphore implementation

// Description: This file contains the implementations of the counting semaphore

//              class.

//

//####DESCRIPTIONEND####

//

//==========================================================================

#include <pkgconf/kernel.h>

#include <cyg/kernel/ktypes.h>         // base kernel types

#include <cyg/infra/cyg_trac.h>        // tracing macros

#include <cyg/infra/cyg_ass.h>         // assertion macros

#include <cyg/kernel/instrmnt.h>       // instrumentation

#include <cyg/kernel/thread.inl>       // Cyg_Thread inlines

#include <cyg/kernel/sema.hxx>         // our header

#include <cyg/kernel/sched.inl>        // scheduler inlines

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

// Constructor

Cyg_Counting_Semaphore::Cyg_Counting_Semaphore(

    cyg_count32 init_count              // Initial count value

    )

{

    count       = init_count;

}

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

// Destructor

Cyg_Counting_Semaphore::~Cyg_Counting_Semaphore()

{

    CYG_ASSERT( queue.empty(), "Destroying semaphore with waiting threads");

}

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

// Wait until the count can be decremented without it becoming

// negative.

cyg_bool Cyg_Counting_Semaphore::wait()

{

    cyg_bool result = true;

    Cyg_Thread *self = Cyg_Thread::self();

    // Prevent preemption

    Cyg_Scheduler::lock();

    CYG_INSTRUMENT_CNTSEM( CLAIM, this, count );

    while( count == 0 && result )

    {

        self->set_sleep_reason( Cyg_Thread::WAIT );

        self->sleep();

        queue.enqueue( self );

        CYG_INSTRUMENT_CNTSEM( WAIT, this, 0 );

        // Allow other threads to run

        Cyg_Scheduler::reschedule();

        CYG_INSTRUMENT_CNTSEM( WOKE, this, count );

        switch( self->get_wake_reason() )

        {

        case Cyg_Thread::DESTRUCT:

        case Cyg_Thread::BREAK:

            result = false;

            break;

        case Cyg_Thread::EXIT:

            self->exit();

            break;

        default:

            break;

        }

    }

    if( result ) count--;

    // Unlock the scheduler

    Cyg_Scheduler::unlock();

    return result;

}

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

// Wait until the count can be decremented without it becoming

// negative.

#ifdef CYGFUN_KERNEL_THREADS_TIMER

cyg_bool

Cyg_Counting_Semaphore::wait( cyg_tick_count timeout )

{

    cyg_bool result = true;

    Cyg_Thread *self = Cyg_Thread::self();

    // Prevent preemption

    Cyg_Scheduler::lock();

    CYG_INSTRUMENT_CNTSEM( CLAIM, this, count );

    // Set the timer _once_ outside the loop.

    self->set_timer( timeout, Cyg_Thread::TIMEOUT  );

    // If the timeout is in the past, the wake reason will have been

    // set to something other than NONE already. If the count is zero,

    // set the result false to force an immediate return. If the count

    // is non-zero, then this wait will succeed anyway.

    if( self->get_wake_reason() != Cyg_Thread::NONE &&

        result = false;

    while ( 0 == count && result ) {

        // must reset the sleep reason every time

        self->set_sleep_reason( Cyg_Thread::TIMEOUT );

        self->sleep();

        queue.enqueue( self );

        CYG_INSTRUMENT_CNTSEM( WAIT, this, 0 );

        // Allow other threads to run

        Cyg_Scheduler::reschedule();

        CYG_INSTRUMENT_CNTSEM( WOKE, this, count );

        switch( self->get_wake_reason() )

        {

        case Cyg_Thread::TIMEOUT:

            result = false;

            CYG_INSTRUMENT_CNTSEM( TIMEOUT, this, count);

            break;

        case Cyg_Thread::DESTRUCT:

        case Cyg_Thread::BREAK:

            result = false;

            break;

        case Cyg_Thread::EXIT:

            self->exit();

            break;

        default:

            break;

        }

    }

    // Clear the timeout. It is irrelevant whether the alarm has

    // actually gone off or not.

    self->clear_timer();

    if ( result ) count--;

    // Unlock the scheduler and maybe switch threads

    Cyg_Scheduler::unlock();

    return result;

}

#endif // CYGFUN_KERNEL_THREADS_TIMER

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

// Try to decrement, but fail if not possible

cyg_bool Cyg_Counting_Semaphore::trywait()

{

    cyg_bool result = true;

    // Prevent preemption

    Cyg_Scheduler::lock();

    if( count > 0 ) count--;

    else            result = false;

    CYG_INSTRUMENT_CNTSEM( TRY, this, result );

    // Unlock the scheduler and maybe switch threads

    Cyg_Scheduler::unlock();

    return result;

}

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

// Increment count

void Cyg_Counting_Semaphore::post()

{

    // Prevent preemption

    Cyg_Scheduler::lock();

    CYG_INSTRUMENT_CNTSEM( POST, this, 0 );

    count++;

    if( !queue.empty() ) {

        // The queue is non-empty, so grab the next

        // thread from it and wake it up. The waiter

        // will decrement the count when he is awakened.

        Cyg_Thread *thread = queue.dequeue();

        thread->set_wake_reason( Cyg_Thread::DONE );

        thread->wake();

        CYG_INSTRUMENT_CNTSEM( WAKE, this, thread );

    }

    // Unlock the scheduler and maybe switch threads

    Cyg_Scheduler::unlock();

}

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

// Get current count value

cyg_count32 Cyg_Counting_Semaphore::peek() const

{

    // This is a single read of the value of count.

    // This is already atomic, hence there is no need

    // to lock the scheduler.

    return count;

}

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

// EOF sync/cnt_sem.cxx