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/*
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* Mutex Handler
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*
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* DESCRIPTION:
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*
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* This package is the implementation of the Mutex Handler.
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* This handler provides synchronization and mutual exclusion capabilities.
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*
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* COPYRIGHT (c) 1989-1999.
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* On-Line Applications Research Corporation (OAR).
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*
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* The license and distribution terms for this file may be
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* found in the file LICENSE in this distribution or at
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* http://www.OARcorp.com/rtems/license.html.
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*
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* $Id: coremutexsurrender.c,v 1.2 2001-09-27 11:59:34 chris Exp $
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*/
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#include <rtems/system.h>
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#include <rtems/score/isr.h>
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#include <rtems/score/coremutex.h>
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#include <rtems/score/states.h>
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#include <rtems/score/thread.h>
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#include <rtems/score/threadq.h>
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/*
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* _CORE_mutex_Surrender
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*
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* DESCRIPTION:
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*
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* This routine frees a unit to the mutex. If a task was blocked waiting for
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* a unit from this mutex, then that task will be readied and the unit
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* given to that task. Otherwise, the unit will be returned to the mutex.
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*
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* Input parameters:
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* the_mutex - the mutex to be flushed
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* id - id of parent mutex
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* api_mutex_mp_support - api dependent MP support actions
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*
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* Output parameters:
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* CORE_MUTEX_STATUS_SUCCESSFUL - if successful
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* core error code - if unsuccessful
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*/
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CORE_mutex_Status _CORE_mutex_Surrender(
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CORE_mutex_Control *the_mutex,
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Objects_Id id,
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CORE_mutex_API_mp_support_callout api_mutex_mp_support
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)
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{
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Thread_Control *the_thread;
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Thread_Control *holder;
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holder = the_mutex->holder;
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/*
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* The following code allows a thread (or ISR) other than the thread
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* which acquired the mutex to release that mutex. This is only
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* allowed when the mutex in quetion is FIFO or simple Priority
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* discipline. But Priority Ceiling or Priority Inheritance mutexes
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* must be released by the thread which acquired them.
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*/
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if ( the_mutex->Attributes.only_owner_release ) {
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if ( !_Thread_Is_executing( holder ) )
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return( CORE_MUTEX_STATUS_NOT_OWNER_OF_RESOURCE );
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}
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/* XXX already unlocked -- not right status */
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if ( !the_mutex->nest_count )
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return( CORE_MUTEX_STATUS_SUCCESSFUL );
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the_mutex->nest_count--;
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if ( the_mutex->nest_count != 0 ) {
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switch ( the_mutex->Attributes.lock_nesting_behavior ) {
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case CORE_MUTEX_NESTING_ACQUIRES:
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return CORE_MUTEX_STATUS_SUCCESSFUL;
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case CORE_MUTEX_NESTING_IS_ERROR:
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/* should never occur */
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return CORE_MUTEX_STATUS_NESTING_NOT_ALLOWED;
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case CORE_MUTEX_NESTING_BLOCKS:
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/* Currently no API exercises this behavior. */
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break;
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}
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}
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_Thread_Executing->resource_count--;
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the_mutex->holder = NULL;
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the_mutex->holder_id = 0;
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/*
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* Whether or not someone is waiting for the mutex, an
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* inherited priority must be lowered if this is the last
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* mutex (i.e. resource) this task has.
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*/
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switch ( the_mutex->Attributes.discipline ) {
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case CORE_MUTEX_DISCIPLINES_FIFO:
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case CORE_MUTEX_DISCIPLINES_PRIORITY:
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break;
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case CORE_MUTEX_DISCIPLINES_PRIORITY_CEILING:
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case CORE_MUTEX_DISCIPLINES_PRIORITY_INHERIT:
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if ( holder->resource_count == 0 &&
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holder->real_priority != holder->current_priority ) {
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_Thread_Change_priority( holder, holder->real_priority, TRUE );
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}
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break;
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}
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if ( ( the_thread = _Thread_queue_Dequeue( &the_mutex->Wait_queue ) ) ) {
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#if defined(RTEMS_MULTIPROCESSING)
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if ( !_Objects_Is_local_id( the_thread->Object.id ) ) {
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the_mutex->holder = NULL;
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the_mutex->holder_id = the_thread->Object.id;
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the_mutex->nest_count = 1;
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( *api_mutex_mp_support)( the_thread, id );
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} else
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#endif
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{
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the_mutex->holder = the_thread;
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the_mutex->holder_id = the_thread->Object.id;
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the_thread->resource_count++;
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the_mutex->nest_count = 1;
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/*
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* No special action for priority inheritance or priority ceiling
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* because the_thread is guaranteed to be the highest priority
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* thread waiting for the mutex.
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*/
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}
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} else
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the_mutex->lock = CORE_MUTEX_UNLOCKED;
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return( CORE_MUTEX_STATUS_SUCCESSFUL );
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}
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