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//==========================================================================
//
//      sync/bin_sem.cxx
//
//      Binary semaphore implementation
//
//==========================================================================
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// -------------------------------------------
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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_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;
}
 
// -------------------------------------------------------------------------
 
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