/****************************************************************************
* sched/sem_holder.c
*
* Copyright (C) 2009 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
*
* 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.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* 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.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <sys/types.h>
#include <semaphore.h>
#include <sched.h>
#include <debug.h>
#include <nuttx/arch.h>
#include "os_internal.h"
#include "sem_internal.h"
#ifdef CONFIG_PRIORITY_INHERITANCE
/****************************************************************************
* Definitions
****************************************************************************/
/* Configuration ************************************************************/
#ifndef CONFIG_SEM_PREALLOCHOLDERS
# define CONFIG_SEM_PREALLOCHOLDERS (4*CONFIG_MAX_TASKS)
#endif
/****************************************************************************
* Private Type Declarations
****************************************************************************/
/****************************************************************************
* Global Variables
****************************************************************************/
/****************************************************************************
* Private Variables
****************************************************************************/
/* Preallocated holder structures */
#if CONFIG_SEM_PREALLOCHOLDERS > 0
static struct semholder_s g_holderalloc[CONFIG_SEM_PREALLOCHOLDERS];
static FAR struct semholder_s *g_freeholders;
#endif
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Function: sem_allocholder
****************************************************************************/
static inline FAR struct semholder_s *sem_allocholder(sem_t *sem)
{
FAR struct semholder_s *pholder;
/* Check if the "built-in" holder is being used. We have this built-in
* holder to optimize for the simplest case where semaphores are only
* used to implement mutexes.
*/
if (!sem->hlist.holder)
{
pholder = &sem->hlist;
}
else
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
pholder = g_freeholders;
if (pholder)
{
/* Remove the holder from the free list an put it into the semaphore's holder list */
g_freeholders = pholder->flink;
pholder->flink = sem->hlist.flink;
sem->hlist.flink = pholder;
/* Make sure the the initial count is zero */
pholder->counts = 0;
}
else
#else
pholder = NULL;
#endif
sdbg("Insufficient pre-allocated holders\n");
}
return pholder;
}
/****************************************************************************
* Function: sem_findholder
****************************************************************************/
static FAR struct semholder_s *sem_findholder(sem_t *sem, FAR _TCB *htcb)
{
FAR struct semholder_s *pholder;
/* Try to find the holder in the list of holders associated with this semaphore */
pholder = &sem->hlist;
#if CONFIG_SEM_PREALLOCHOLDERS > 0
for (; pholder; pholder = pholder->flink)
#endif
{
if (pholder->holder == htcb)
{
/* Got it! */
return pholder;
}
}
/* The holder does not appear in the list */
return NULL;
}
/****************************************************************************
* Function: sem_findorallocateholder
****************************************************************************/
static inline FAR struct semholder_s *sem_findorallocateholder(sem_t *sem, FAR _TCB *htcb)
{
FAR struct semholder_s *pholder = sem_findholder(sem, htcb);
if (!pholder)
{
pholder = sem_allocholder(sem);
}
return pholder;
}
/****************************************************************************
* Function: sem_freeholder
****************************************************************************/
static inline void sem_freeholder(sem_t *sem, FAR struct semholder_s *pholder)
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
FAR struct semholder_s *curr;
FAR struct semholder_s *prev;
#endif
/* Release the holder and counts */
pholder->holder = 0;
pholder->counts = 0;
#if CONFIG_SEM_PREALLOCHOLDERS > 0
/* If this is the holder inside the semaphore, then do nothing more */
if (pholder != &sem->hlist)
{
/* Otherwise, search the list for the matching holder */
for (prev = &sem->hlist, curr = sem->hlist.flink;
curr && curr != pholder;
prev = curr, curr = curr->flink);
if (curr)
{
/* Remove the holder from the list */
prev->flink = pholder->flink;
/* And put it in the free list */
pholder->flink = g_freeholders;
g_freeholders = pholder;
}
}
#endif
}
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Function: sem_initholders
*
* Description:
* Called from sem_initialize() to set up semaphore holder information.
*
* Parameters:
* None
*
* Return Value:
* None
*
* Assumptions:
*
****************************************************************************/
void sem_initholders(void)
{
#ifdef CONFIG_SEM_PREALLOCHOLDERS
int i;
/* Put all of the pre-allocated holder structures into free list */
g_freeholders = g_holderalloc;
for (i = 0; i < (CONFIG_SEM_PREALLOCHOLDERS-1); i++)
{
g_holderalloc[i].flink = &g_holderalloc[i+1];
}
g_holderalloc[CONFIG_SEM_PREALLOCHOLDERS-1].flink = NULL;
#endif
}
/****************************************************************************
* Function: sem_destroyholder
*
* Description:
* Called from sem_destroy() to handle any holders of a semaphore when
* it is destroyed.
*
* Parameters:
* sem - A reference to the semaphore being destroyed
*
* Return Value:
* None
*
* Assumptions:
*
****************************************************************************/
void sem_destroyholder(sem_t *sem)
{
#if 0
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
/* It is an error is a semaphore is destroyed while there are any holders
* (except perhaps the thread releas the semaphore itself). Hmmm.. but
* we actually have to assume that the caller knows what it is doing because
* could have killed another thread that is the actual holder of the semaphore.
*/
#if CONFIG_SEM_PREALLOCHOLDERS > 0
DEBUGASSERT((!sem->hlist.holder || sem->hlist.holder == rtcb) && !sem->hlist.flink);
#else
DEBUGASSERT(!sem->hlist.holder || sem->hlist.holder == rtcb);
#endif
#endif
sem->hlist.holder = NULL;
}
/****************************************************************************
* Function: sem_addholder
*
* Description:
* Called from sem_wait() when the calling thread obtains the semaphore
*
* Parameters:
* sem - A reference to the incremented semaphore
*
* Return Value:
* 0 (OK) or -1 (ERROR) if unsuccessful
*
* Assumptions:
*
****************************************************************************/
void sem_addholder(sem_t *sem)
{
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
FAR struct semholder_s *pholder;
/* Find or allocate a container for this new holder */
pholder = sem_findorallocateholder(sem, rtcb);
if (pholder)
{
/* Then set the holder and increment the number of counts held by this holder */
pholder->holder = rtcb;
pholder->counts++;
}
}
/****************************************************************************
* Function: void sem_boostpriority(sem_t *sem)
*
* Description:
*
*
* Parameters:
* None
*
* Return Value:
* 0 (OK) or -1 (ERROR) if unsuccessful
*
* Assumptions:
*
****************************************************************************/
void sem_boostpriority(sem_t *sem)
{
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
FAR _TCB *htcb;
struct semholder_s *pholder;
/* Traverse the list of holders */
pholder = &sem->hlist;
#if CONFIG_SEM_PREALLOCHOLDERS > 0
for (; pholder; pholder = pholder->flink)
#endif
{
/* As an artifact, there will be holders that have no counts. This
* because they have posted the semaphore and there count was decrement
* by sem_releaseholder(), but they are still being retained in the
* list to be harvested by sem_restorebaseprio.
*/
if (pholder->counts > 0)
{
htcb = pholder->holder;
if (htcb && htcb->sched_priority < rtcb->sched_priority)
{
/* Raise the priority of the holder of the semaphore. This
* cannot cause a context switch because we have preemption
* disabled. The task will be marked "pending" and the switch
* will occur during up_block_task() processing.
*
* NOTE that we have to restore base_priority because
* sched_setparam() should set both.
*/
int base_priority = htcb->base_priority;
(void)sched_settcbprio(htcb, rtcb->sched_priority);
htcb->base_priority = base_priority;
}
}
}
}
/****************************************************************************
* Function: sem_releaseholder
*
* Description:
* Called from sem_post() after a thread releases one count on the
* semaphore.
*
* Parameters:
* sem - A reference to the semaphore being posted
*
* Return Value:
* None
*
* Assumptions:
*
****************************************************************************/
void sem_releaseholder(sem_t *sem)
{
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
FAR struct semholder_s *pholder;
/* Find the container for this holder */
pholder = sem_findholder(sem, rtcb);
if (pholder && pholder->counts > 0)
{
/* Decrement the counts on this holder */
pholder->counts--;
}
}
/****************************************************************************
* Function: sem_restorebaseprio
*
* Description:
* Check if we need to drop the priority of any threads holding the
* semaphore. The priority could have been boosted while they held the
* semaphore.
*
* Parameters:
* sem - A reference to the semaphore being posted
*
* Return Value:
* 0 (OK) or -1 (ERROR) if unsuccessful
*
* Assumptions:
*
****************************************************************************/
void sem_restorebaseprio(sem_t *sem)
{
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
FAR _TCB *htcb;
struct semholder_s *pholder;
#if CONFIG_SEM_PREALLOCHOLDERS > 0
struct semholder_s *next;
#endif
/* Check if the semaphore is still available */
if (sem->semcount > 0)
{
/* Traverse the list of holders */
pholder = &sem->hlist;
#if CONFIG_SEM_PREALLOCHOLDERS > 0
for (; pholder; pholder = next)
#endif
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
next = pholder->flink; /* In case pholder gets deleted */
#endif
/* The initial "built-in" container may hold a NULL holder */
htcb = pholder->holder;
if (htcb)
{
/* Was the priority of this thread boosted? NOTE: There is
* a logical flaw here: If the thread holds multiple semaphore
* and has been boosted multiple times, then there is no mechanism
* to know the correct priority to restore and we may error in
* prematurely lowering the priority.
*/
if (htcb->sched_priority != htcb->base_priority)
{
up_reprioritize_rtr(rtcb, htcb->base_priority);
}
/* When no more counts are held, remove the holder from the list */
if (pholder->counts <= 0)
{
sem_freeholder(sem, pholder);
}
}
}
}
}
#endif /* CONFIG_PRIORITY_INHERITANCE */
