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

//

//      sync/bin_sem.cxx

//

//      Binary semaphore implementation

//

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

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

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

//

// Author(s):   nickg

// Contributors:        nickg

// Date:        1997-09-24

// Purpose:     Cyg_Binary_Semaphore implementation

// Description: This file contains the implementations of the binary 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

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

Cyg_Binary_Semaphore::Cyg_Binary_Semaphore (

    cyg_bool    init_state

)

{

    state       = init_state;

}

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

Cyg_Binary_Semaphore::~Cyg_Binary_Semaphore ( )

{

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

}

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

cyg_bool Cyg_Binary_Semaphore::wait()

{

    cyg_bool result = true;

    Cyg_Thread *self = Cyg_Thread::self();

    // Prevent preemption

    Cyg_Scheduler::lock();

    CYG_INSTRUMENT_BINSEM( CLAIM, this, state );

    while( !state && result )

    {

        self->set_sleep_reason( Cyg_Thread::WAIT );

        self->sleep();

        queue.enqueue( self );

        CYG_INSTRUMENT_BINSEM( WAIT, this, 0 );

        // Allow other threads to run

        Cyg_Scheduler::reschedule();

        CYG_INSTRUMENT_BINSEM( WOKE, this, state );

        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 ) state = false;

    // Unlock the scheduler and maybe switch threads

    Cyg_Scheduler::unlock();

    return result;

}

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

// Wait until the state can be set false or timeout

#ifdef CYGFUN_KERNEL_THREADS_TIMER

cyg_bool

Cyg_Binary_Semaphore::wait( cyg_tick_count timeout )

{

    cyg_bool result = true;

    Cyg_Thread *self = Cyg_Thread::self();

    // Prevent preemption

    Cyg_Scheduler::lock();

    CYG_INSTRUMENT_BINSEM( CLAIM, this, state );

    // 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 semaphore is

    // not available, set the result false to force an immediate

    // return. If it is available, then go ahead and claim it.

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

        result = false;

    while ( !state && result ) {

        // must reset the sleep reason every time

        self->set_sleep_reason( Cyg_Thread::TIMEOUT );

        self->sleep();

        queue.enqueue( self );

        CYG_INSTRUMENT_BINSEM( WAIT, this, 0 );

        // Allow other threads to run

        Cyg_Scheduler::reschedule();

        CYG_INSTRUMENT_BINSEM( WOKE, this, state );

        switch( self->get_wake_reason() )

        {

        case Cyg_Thread::TIMEOUT:

            result = false;

            CYG_INSTRUMENT_BINSEM( TIMEOUT, this, state);

            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 ) state = false;

    // Unlock the scheduler and maybe switch threads

    Cyg_Scheduler::unlock();

    return result;

}

#endif // CYGFUN_KERNEL_THREADS_TIMER

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

cyg_bool Cyg_Binary_Semaphore::trywait()

{

    cyg_bool result = true;

    // Prevent preemption

    Cyg_Scheduler::lock();

    if( state ) state = false;

    else        result = false;

    CYG_INSTRUMENT_BINSEM( TRY, this, result );

    // Unlock the scheduler and maybe switch threads

    Cyg_Scheduler::unlock();

    return result;

}

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

void Cyg_Binary_Semaphore::post()

{

    // Prevent preemption

    Cyg_Scheduler::lock();

    CYG_INSTRUMENT_BINSEM( POST, this, 0 );

    state = true;

    if( !queue.empty() ) {

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

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

        // will clear the flag.

        Cyg_Thread *thread = queue.dequeue();

        thread->set_wake_reason( Cyg_Thread::DONE );

        thread->wake();

        CYG_INSTRUMENT_BINSEM( WAKE, this, thread );

    }

    // Unlock the scheduler and maybe switch threads

    Cyg_Scheduler::unlock();

}

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

cyg_bool Cyg_Binary_Semaphore::posted()

{

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

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

    // to lock the scheduler.

    return state;

}

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

// EOF sync/bin_sem.cxx