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/* SPDX-License-Identifier: BSD-2-Clause */
/**
* @file
*
* @ingroup RTEMSScoreFutex
*
* @brief This source file contains the implementation of
* _Futex_Wait() and _Futex_Wake().
*/
/*
* Copyright (C) 2015, 2016 embedded brains GmbH & Co. KG
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/**
* @defgroup RTEMSScoreFutex Futex Handler
*
* @ingroup RTEMSScore
*
* @brief This group contains the Futex Handler implementation.
*
* The behaviour of the futex operations is defined by Linux, see also:
*
* https://man7.org/linux/man-pages/man2/futex.2.html
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <sys/lock.h>
#include <errno.h>
#include <rtems/score/atomic.h>
#include <rtems/score/chainimpl.h>
#include <rtems/score/threadimpl.h>
#include <rtems/score/threadqimpl.h>
#define FUTEX_TQ_OPERATIONS &_Thread_queue_Operations_FIFO
typedef struct {
Thread_queue_Syslock_queue Queue;
} Futex_Control;
RTEMS_STATIC_ASSERT(
offsetof( Futex_Control, Queue )
== offsetof( struct _Futex_Control, _Queue ),
FUTEX_CONTROL_QUEUE
);
RTEMS_STATIC_ASSERT(
sizeof( Futex_Control ) == sizeof( struct _Futex_Control ),
FUTEX_CONTROL_SIZE
);
static Futex_Control *_Futex_Get( struct _Futex_Control *_futex )
{
return (Futex_Control *) _futex;
}
static Thread_Control *_Futex_Queue_acquire_critical(
Futex_Control *futex,
Thread_queue_Context *queue_context
)
{
Thread_Control *executing;
executing = _Thread_Executing;
_Thread_queue_Queue_acquire_critical(
&futex->Queue.Queue,
&executing->Potpourri_stats,
&queue_context->Lock_context.Lock_context
);
return executing;
}
static void _Futex_Queue_release(
Futex_Control *futex,
ISR_Level level,
Thread_queue_Context *queue_context
)
{
_Thread_queue_Queue_release_critical(
&futex->Queue.Queue,
&queue_context->Lock_context.Lock_context
);
_ISR_Local_enable( level );
}
/**
* @brief Performs the ``FUTEX_WAIT`` operation.
*
* @param[in, out] _futex is the futex object.
*
* @param[in] uaddr is the address to the futex state.
*
* @param val is the expected futex state value.
*
* @retval 0 Returns zero if the futex state is equal to the expected value.
* In this case the calling thread is enqueued on the thread queue of the
* futex object.
*
* @retval EAGAIN Returns EAGAIN if the futex state is not equal to the
* expected value.
*/
int _Futex_Wait( struct _Futex_Control *_futex, int *uaddr, int val )
{
Futex_Control *futex;
ISR_Level level;
Thread_queue_Context queue_context;
Thread_Control *executing;
int eno;
futex = _Futex_Get( _futex );
_Thread_queue_Context_initialize( &queue_context );
_Thread_queue_Context_ISR_disable( &queue_context, level );
executing = _Futex_Queue_acquire_critical( futex, &queue_context );
if ( *uaddr == val ) {
_Thread_queue_Context_set_thread_state(
&queue_context,
STATES_WAITING_FOR_FUTEX
);
_Thread_queue_Context_set_enqueue_do_nothing_extra( &queue_context );
_Thread_queue_Context_set_ISR_level( &queue_context, level );
_Thread_queue_Enqueue(
&futex->Queue.Queue,
FUTEX_TQ_OPERATIONS,
executing,
&queue_context
);
eno = 0;
} else {
_Futex_Queue_release( futex, level, &queue_context );
eno = EAGAIN;
}
return eno;
}
typedef struct {
Thread_queue_Context Base;
int count;
} Futex_Context;
static Thread_Control *_Futex_Flush_filter(
Thread_Control *the_thread,
Thread_queue_Queue *queue,
Thread_queue_Context *queue_context
)
{
Futex_Context *context;
context = (Futex_Context *) queue_context;
if ( context->count <= 0 ) {
return NULL;
}
--context->count;
return the_thread;
}
/**
* @brief Performs the ``FUTEX_WAKE`` operation.
*
* @param[in, out] _futex is the futex object.
*
* @param count is the maximum count of threads to wake up.
*
* @return Returns the count of woken up threads.
*/
int _Futex_Wake( struct _Futex_Control *_futex, int count )
{
Futex_Control *futex;
ISR_Level level;
Futex_Context context;
futex = _Futex_Get( _futex );
_Thread_queue_Context_initialize( &context.Base );
_Thread_queue_Context_ISR_disable( &context.Base, level );
_Futex_Queue_acquire_critical( futex, &context.Base );
/*
* For some synchronization objects like barriers the _Futex_Wake() must be
* called in the fast path. Normally there are no threads on the queue, so
* check this condition early.
*/
if ( RTEMS_PREDICT_TRUE( _Thread_queue_Is_empty( &futex->Queue.Queue ) ) ) {
_Futex_Queue_release( futex, level, &context.Base );
return 0;
}
context.count = count;
_Thread_queue_Context_set_ISR_level( &context.Base, level );
return (int) _Thread_queue_Flush_critical(
&futex->Queue.Queue,
FUTEX_TQ_OPERATIONS,
_Futex_Flush_filter,
&context.Base
);
}
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