cnt_sem.cxx

ecos为实时嵌入式操作系统

//==========================================================================
//
//      sync/cnt_sem.cxx
//
//      Counting semaphore implementation
//
//==========================================================================
//####COPYRIGHTBEGIN####
//
// -------------------------------------------
// The contents of this file are subject to the Cygnus eCos Public License
// Version 1.0 (the "License"); you may not use this file except in
// compliance with the License.  You may obtain a copy of the License at
// http://sourceware.cygnus.com/ecos
// 
// Software distributed under the License is distributed on an "AS IS"
// basis, WITHOUT WARRANTY OF ANY KIND, either express or implied.  See the
// License for the specific language governing rights and limitations under
// the License.
// 
// The Original Code is eCos - Embedded Cygnus Operating System, released
// September 30, 1998.
// 
// The Initial Developer of the Original Code is Cygnus.  Portions created
// by Cygnus are Copyright (C) 1998,1999 Cygnus Solutions.  All Rights Reserved.
// -------------------------------------------
//
//####COPYRIGHTEND####
//==========================================================================
//#####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 );

        CYG_ASSERT( Cyg_Scheduler::get_sched_lock() == 1, "Called with non-zero scheduler lock");
        
        Cyg_Scheduler::unlock();
        Cyg_Scheduler::lock();

        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. Set the result false
    // to force an immediate return.
    
    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 );

        CYG_ASSERT( Cyg_Scheduler::get_sched_lock() == 1,
                    "Called with non-zero scheduler lock");
        
        Cyg_Scheduler::unlock();
        Cyg_Scheduler::lock();

        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()
{
    // 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