diff packages/kernel/current/src/sync/cnt_sem.cxx @ 0:3111d98ba7b3 ecos-v1_1-release

Initial commit of eCos version 1.1
author jlarmour
date Tue, 11 May 1999 11:16:07 +0000
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children 443894e2e912
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+//==========================================================================
+//
+//	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 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