path: root/cpukit/score/src/semaphore.c

/*
 * Copyright (c) 2015 embedded brains GmbH.  All rights reserved.
 *
 *  embedded brains GmbH
 *  Dornierstr. 4
 *  82178 Puchheim
 *  Germany
 *  <rtems@embedded-brains.de>
 *
 * The license and distribution terms for this file may be
 * found in the file LICENSE in this distribution or at
 * http://www.rtems.org/license/LICENSE.
 */

#if HAVE_CONFIG_H
  #include "config.h"
#endif

#if HAVE_STRUCT__THREAD_QUEUE_QUEUE

#include <sys/lock.h>

#include <rtems/score/assert.h>
#include <rtems/score/threadimpl.h>
#include <rtems/score/threadqimpl.h>

#define SEMAPHORE_TQ_OPERATIONS &_Thread_queue_Operations_priority

typedef struct {
  Thread_queue_Syslock_queue Queue;
  unsigned int count;
} Semaphore_Control;

RTEMS_STATIC_ASSERT(
  offsetof( Semaphore_Control, Queue )
    == offsetof( struct _Semaphore_Control, _Queue ),
  SEMAPHORE_CONTROL_QUEUE
);

RTEMS_STATIC_ASSERT(
  offsetof( Semaphore_Control, count )
    == offsetof( struct _Semaphore_Control, _count ),
  SEMAPHORE_CONTROL_COUNT
);

RTEMS_STATIC_ASSERT(
  sizeof( Semaphore_Control ) == sizeof( struct _Semaphore_Control ),
  SEMAPHORE_CONTROL_SIZE
);

static Semaphore_Control *_Semaphore_Get(
  struct _Semaphore_Control *_sem
)
{
  return (Semaphore_Control *) _sem;
}

static Thread_Control *_Semaphore_Queue_acquire_critical(
  Semaphore_Control    *sem,
  Thread_queue_Context *queue_context
)
{
  Thread_Control *executing;

  executing = _Thread_Executing;
  _Thread_queue_Queue_acquire_critical(
    &sem->Queue.Queue,
    &executing->Potpourri_stats,
    &queue_context->Lock_context.Lock_context
  );

  return executing;
}

static void _Semaphore_Queue_release(
  Semaphore_Control    *sem,
  ISR_Level             level,
  Thread_queue_Context *queue_context
)
{
  _Thread_queue_Queue_release_critical(
    &sem->Queue.Queue,
    &queue_context->Lock_context.Lock_context
  );
  _ISR_Local_enable( level );
}

void _Semaphore_Wait( struct _Semaphore_Control *_sem )
{
  Semaphore_Control    *sem ;
  ISR_Level             level;
  Thread_queue_Context  queue_context;
  Thread_Control       *executing;
  unsigned int          count;

  sem = _Semaphore_Get( _sem );
  _Thread_queue_Context_initialize( &queue_context );
  _Thread_queue_Context_ISR_disable( &queue_context, level );
  executing = _Semaphore_Queue_acquire_critical( sem, &queue_context );

  count = sem->count;
  if ( __predict_true( count > 0 ) ) {
    sem->count = count - 1;
    _Semaphore_Queue_release( sem, level, &queue_context );
  } else {
    _Thread_queue_Context_set_expected_level( &queue_context, 1 );
    _Thread_queue_Context_set_no_timeout( &queue_context );
    _Thread_queue_Context_set_ISR_level( &queue_context, level );
    _Thread_queue_Enqueue_critical(
      &sem->Queue.Queue,
      SEMAPHORE_TQ_OPERATIONS,
      executing,
      STATES_WAITING_FOR_SYS_LOCK_SEMAPHORE,
      &queue_context
    );
  }
}

void _Semaphore_Post( struct _Semaphore_Control *_sem )
{
  Semaphore_Control    *sem;
  ISR_Level             level;
  Thread_queue_Context  queue_context;
  Thread_queue_Heads   *heads;

  sem = _Semaphore_Get( _sem );
  _Thread_queue_Context_initialize( &queue_context );
  _Thread_queue_Context_ISR_disable( &queue_context, level );
  _Semaphore_Queue_acquire_critical( sem, &queue_context );

  heads = sem->Queue.Queue.heads;
  if ( __predict_true( heads == NULL ) ) {
    _Assert( sem->count < UINT_MAX );
    ++sem->count;
    _Semaphore_Queue_release( sem, level, &queue_context );
  } else {
    const Thread_queue_Operations *operations;
    Thread_Control *first;

    _Thread_queue_Context_set_ISR_level( &queue_context, level );
    operations = SEMAPHORE_TQ_OPERATIONS;
    first = ( *operations->first )( heads );

    _Thread_queue_Extract_critical(
      &sem->Queue.Queue,
      operations,
      first,
      &queue_context
    );
  }
}

#endif /* HAVE_STRUCT__THREAD_QUEUE_QUEUE */