bin_sem.cxx

来自「eCos操作系统源码」· CXX 代码 · 共 277 行

//==========================================================================
//
//      sync/bin_sem.cxx
//
//      Binary semaphore implementation
//
//==========================================================================
//####ECOSGPLCOPYRIGHTBEGIN####
// -------------------------------------------
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// Copyright (C) 1998, 1999, 2000, 2001, 2002 Red Hat, Inc.
//
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// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
// for more details.
//
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// 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
//
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// or inline functions from this file, or you compile this file and link it
// with other works to produce a work based on this file, this file does not
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//####ECOSGPLCOPYRIGHTEND####
//==========================================================================
//#####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