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incubator-nuttx/sched/semaphore/sem_holder.c

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/****************************************************************************
* sched/semaphore/sem_holder.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <sched.h>
#include <assert.h>
#include <debug.h>
#include <nuttx/addrenv.h>
#include <nuttx/arch.h>
#include "sched/sched.h"
#include "semaphore/semaphore.h"
#ifdef CONFIG_PRIORITY_INHERITANCE
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/* Configuration ************************************************************/
#ifndef CONFIG_SEM_PREALLOCHOLDERS
# define CONFIG_SEM_PREALLOCHOLDERS 0
#endif
/****************************************************************************
* Private Type Declarations
****************************************************************************/
typedef int (*holderhandler_t)(FAR struct semholder_s *pholder,
FAR sem_t *sem, FAR void *arg);
/****************************************************************************
* Private Data
****************************************************************************/
/* 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
/****************************************************************************
* Name: nxsem_allocholder
****************************************************************************/
static inline FAR struct semholder_s *
nxsem_allocholder(FAR sem_t *sem, FAR struct tcb_s *htcb)
{
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 CONFIG_SEM_PREALLOCHOLDERS > 0
pholder = g_freeholders;
if (pholder != NULL)
{
/* Remove the holder from the free list and
* put it into the semaphore's holder list
*/
g_freeholders = pholder->flink;
pholder->flink = sem->hhead;
sem->hhead = pholder;
}
#else
if (sem->holder.htcb == NULL)
{
pholder = &sem->holder;
}
#endif
else
{
serr("ERROR: Insufficient pre-allocated holders\n");
PANIC();
}
pholder->sem = sem;
pholder->htcb = htcb;
pholder->counts = 0;
/* Put it into the task's list */
pholder->tlink = htcb->holdsem;
htcb->holdsem = pholder;
return pholder;
}
/****************************************************************************
* Name: nxsem_findholder
*
* NOTE: htcb may be used only as a look-up key. It certain cases, the task
* may have exited and htcb may refer to a stale memory. It must not be
* dereferenced.
*
****************************************************************************/
static FAR struct semholder_s *
nxsem_findholder(FAR sem_t *sem, FAR struct tcb_s *htcb)
{
FAR struct semholder_s *pholder;
#if CONFIG_SEM_PREALLOCHOLDERS > 0
/* Try to find the holder in the list of holders associated with this
* semaphore
*/
for (pholder = sem->hhead; pholder != NULL; pholder = pholder->flink)
{
if (pholder->htcb == htcb)
{
/* Got it! */
return pholder;
}
}
#else
/* We have one hard-allocated holder structures in sem_t */
pholder = &sem->holder;
if (pholder->htcb == htcb)
{
/* Got it! */
return pholder;
}
#endif
/* The holder does not appear in the list */
return NULL;
}
/****************************************************************************
* Name: nxsem_findorallocateholder
****************************************************************************/
static inline FAR struct semholder_s *
nxsem_findorallocateholder(FAR sem_t *sem, FAR struct tcb_s *htcb)
{
FAR struct semholder_s *pholder = nxsem_findholder(sem, htcb);
if (pholder == NULL)
{
pholder = nxsem_allocholder(sem, htcb);
}
return pholder;
}
/****************************************************************************
* Name: nxsem_freeholder
****************************************************************************/
static inline void nxsem_freeholder(FAR sem_t *sem,
FAR struct semholder_s *pholder)
{
FAR struct semholder_s * FAR *curr;
/* Remove the holder from the task's list */
for (curr = &pholder->htcb->holdsem;
*curr != NULL;
curr = &(*curr)->tlink)
{
if (*curr == pholder)
{
*curr = pholder->tlink;
break;
}
}
/* Release the holder and counts */
pholder->tlink = NULL;
pholder->sem = NULL;
pholder->htcb = NULL;
pholder->counts = 0;
#if CONFIG_SEM_PREALLOCHOLDERS > 0
/* Remove the holder from the semaphore's list */
for (curr = &sem->hhead;
*curr != NULL;
curr = &(*curr)->flink)
{
if (*curr == pholder)
{
*curr = pholder->flink;
break;
}
}
/* And put it in the free list */
pholder->flink = g_freeholders;
g_freeholders = pholder;
#endif
}
/****************************************************************************
* Name: nxsem_freecount0holder
****************************************************************************/
#if CONFIG_SEM_PREALLOCHOLDERS > 0
static int nxsem_freecount0holder(FAR struct semholder_s *pholder,
FAR sem_t *sem, FAR void *arg)
{
/* When no more counts are held, remove the holder from the list. The
* count was decremented in nxsem_release_holder.
*/
if (pholder->counts <= 0)
{
nxsem_freeholder(sem, pholder);
return 1;
}
return 0;
}
#endif
/****************************************************************************
* Name: nxsem_foreachholder
****************************************************************************/
static int nxsem_foreachholder(FAR sem_t *sem, holderhandler_t handler,
FAR void *arg)
{
FAR struct semholder_s *pholder;
int ret = 0;
#if CONFIG_SEM_PREALLOCHOLDERS > 0
FAR struct semholder_s *next;
for (pholder = sem->hhead; pholder && ret == 0; pholder = next)
{
/* In case this holder gets deleted */
next = pholder->flink;
DEBUGASSERT(pholder->htcb != NULL);
/* Call the handler */
ret = handler(pholder, sem, arg);
}
#else
/* We have one hard-allocated holder structures in sem_t */
pholder = &sem->holder;
/* The hard-allocated containers may hold a NULL holder */
if (pholder->htcb != NULL)
{
/* Call the handler */
ret = handler(pholder, sem, arg);
}
#endif
return ret;
}
/****************************************************************************
* Name: nxsem_recoverholders
****************************************************************************/
static int nxsem_recoverholders(FAR struct semholder_s *pholder,
FAR sem_t *sem, FAR void *arg)
{
nxsem_freeholder(sem, pholder);
return 0;
}
/****************************************************************************
* Name: nxsem_boostholderprio
****************************************************************************/
static int nxsem_boostholderprio(FAR struct semholder_s *pholder,
FAR sem_t *sem, FAR void *arg)
{
FAR struct tcb_s *htcb = pholder->htcb;
FAR struct tcb_s *rtcb = (FAR struct tcb_s *)arg;
/* If the priority of the thread that is waiting for a count is less than
* or equal to the priority of the thread holding a count, then do nothing
* because the thread is already running at a sufficient priority.
*/
if (rtcb->sched_priority > htcb->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_contex_switch() processing.
*/
nxsched_set_priority(htcb, rtcb->sched_priority);
}
return 0;
}
/****************************************************************************
* Name: nxsem_verifyholder
****************************************************************************/
#ifdef CONFIG_DEBUG_ASSERTIONS
static int nxsem_verifyholder(FAR struct semholder_s *pholder,
FAR sem_t *sem, FAR void *arg)
{
/* Need to revisit this, but these assumptions seem to be untrue -- OR
* there is a bug???
*/
#if 0
FAR struct tcb_s *htcb = pholder->htcb;
/* Called after a semaphore has been released (incremented), the semaphore
* could be non-negative, and there is no thread waiting for the count.
* In this case, the priority of the holder should not be boosted.
*/
DEBUGASSERT(htcb->sched_priority == htcb->base_priority);
#endif
return 0;
}
#endif
/****************************************************************************
* Name: nxsem_dumpholder
****************************************************************************/
#if defined(CONFIG_DEBUG_INFO) && defined(CONFIG_SEM_PHDEBUG)
static int nxsem_dumpholder(FAR struct semholder_s *pholder, FAR sem_t *sem,
FAR void *arg)
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
_info(" %08x: %08x %08x %08x %08x %04x\n",
pholder, pholder->flink,
#else
_info(" %08x: %08x %08x %08x %04x\n",
pholder,
#endif
pholder->tlink, pholder->sem, pholder->htcb, pholder->counts);
return 0;
}
#endif
/****************************************************************************
* Name: nxsem_restore_priority
****************************************************************************/
static void nxsem_restore_priority(FAR struct tcb_s *htcb)
{
int hpriority;
/* We attempt to restore thread priority to its base priority. If
* there is any thread with the higher priority waiting for the
* semaphore held by htcb then this value will be overwritten.
*/
hpriority = htcb->boost_priority > htcb->base_priority ?
htcb->boost_priority : htcb->base_priority;
/* Was the priority of the holder thread boosted? If so, then drop its
* priority back to the correct level. What is the correct level?
*/
if (htcb->sched_priority != hpriority)
{
FAR struct semholder_s *pholder;
#ifdef CONFIG_ARCH_ADDRENV
FAR struct addrenv_s *oldenv;
if (htcb->addrenv_own)
{
addrenv_select(htcb->addrenv_own, &oldenv);
}
#endif
/* Try to find the highest priority across all the threads that are
* waiting for any semaphore held by htcb.
*/
for (pholder = htcb->holdsem; pholder != NULL;
pholder = pholder->tlink)
{
FAR struct tcb_s *stcb;
stcb = (FAR struct tcb_s *)dq_peek(SEM_WAITLIST(pholder->sem));
if (stcb != NULL && stcb->sched_priority > hpriority)
{
hpriority = stcb->sched_priority;
}
}
#ifdef CONFIG_ARCH_ADDRENV
if (htcb->addrenv_own)
{
addrenv_restore(oldenv);
}
#endif
/* Apply the selected priority to the thread (hopefully back to the
* threads base_priority).
*/
nxsched_set_priority(htcb, hpriority);
}
}
/****************************************************************************
* Name: nxsem_restoreholderprio
****************************************************************************/
static int nxsem_restoreholderprio(FAR struct semholder_s *pholder,
FAR sem_t *sem, FAR void *arg)
{
FAR struct tcb_s *htcb = pholder->htcb;
/* Release the holder if all counts have been given up
* before reprioritizing causes a context switch.
*/
if (pholder->counts <= 0)
{
nxsem_freeholder(sem, pholder);
}
nxsem_restore_priority(htcb);
return 0;
}
#if CONFIG_SEM_PREALLOCHOLDERS > 0
/****************************************************************************
* Name: nxsem_restoreholderprio_others
*
* Description:
* Reprioritize all holders except the currently executing task
*
****************************************************************************/
static int nxsem_restoreholderprio_others(FAR struct semholder_s *pholder,
FAR sem_t *sem, FAR void *arg)
{
FAR struct tcb_s *rtcb = this_task();
if (pholder->htcb != rtcb)
{
return nxsem_restoreholderprio(pholder, sem, arg);
}
return 0;
}
/****************************************************************************
* Name: nxsem_restoreholderprio_self
*
* Description:
* Reprioritize only the currently executing task
*
****************************************************************************/
static int nxsem_restoreholderprio_self(FAR struct semholder_s *pholder,
FAR sem_t *sem, FAR void *arg)
{
FAR struct tcb_s *rtcb = this_task();
if (pholder->htcb == rtcb)
{
/* The running task has given up a count on the semaphore */
nxsem_restoreholderprio(pholder, sem, arg);
return 1;
}
return 0;
}
#endif
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: nxsem_initialize_holders
*
* Description:
* Called from nxsem_initialize() to set up semaphore holder information.
*
* Input Parameters:
* None
*
* Returned Value:
* None
*
* Assumptions:
*
****************************************************************************/
void nxsem_initialize_holders(void)
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
int i;
/* Put all of the pre-allocated holder structures into the 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
}
/****************************************************************************
* Name: nxsem_destroyholder
*
* Description:
* Called from nxsem_destroy() to handle any holders of a semaphore
* when it is destroyed.
*
* Input Parameters:
* sem - A reference to the semaphore being destroyed
*
* Returned Value:
* None
*
* Assumptions:
*
****************************************************************************/
void nxsem_destroyholder(FAR sem_t *sem)
{
/* It might be an error if a semaphore is destroyed while there are any
* holders of the semaphore (except perhaps the thread that release the
* semaphore itself). 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.
*
* It is also a standard practice to destroy the semaphore while the
* caller holds it. Of course, the caller MUST assure that there are no
* other holders of the semaphore in this case. This occurs, for example,
* when a driver is unlink'ed and the driver instance must be destroyed.
*
* Therefore, we cannot make any assumptions about the state of the
* semaphore or the state of any of the holder threads. So just recover
* any stranded holders and hope the task knows what it is doing.
*/
#if CONFIG_SEM_PREALLOCHOLDERS > 0
if (sem->hhead != NULL)
{
/* There may be an issue if there are multiple holders of
* the semaphore.
*/
DEBUGASSERT(sem->hhead->flink == NULL);
}
#else
/* There may be an issue if there are multiple holders of the semaphore. */
DEBUGASSERT(sem->holder.htcb == NULL);
#endif
nxsem_foreachholder(sem, nxsem_recoverholders, NULL);
}
/****************************************************************************
* Name: nxsem_add_holder_tcb
*
* Description:
* Called from nxsem_wait() when the calling thread obtains the semaphore;
* Called from sem_post() when the waiting thread obtains the semaphore.
*
* Input Parameters:
* htcb - TCB of the thread that just obtained the semaphore
* sem - A reference to the incremented semaphore
*
* Returned Value:
* 0 (OK) or -1 (ERROR) if unsuccessful
*
* Assumptions:
* Interrupts are disabled.
*
****************************************************************************/
void nxsem_add_holder_tcb(FAR struct tcb_s *htcb, FAR sem_t *sem)
{
FAR struct semholder_s *pholder;
uint8_t prioinherit = sem->flags & SEM_PRIO_MASK;
/* If priority inheritance is disabled for this thread or it is IDLE
* thread, then do not add the holder.
* If there are never holders of the semaphore, the priority
* inheritance is effectively disabled.
*/
if (!is_idle_task(htcb) && prioinherit == SEM_PRIO_INHERIT)
{
/* Find or allocate a container for this new holder */
pholder = nxsem_findorallocateholder(sem, htcb);
if (pholder->counts < SEM_VALUE_MAX)
{
/* Increment the number of counts held by this holder */
pholder->counts++;
}
}
}
/****************************************************************************
* Name: nxsem_add_holder
*
* Description:
* Called from nxsem_wait() when the calling thread obtains the semaphore
*
* Input Parameters:
* sem - A reference to the incremented semaphore
*
* Returned Value:
* 0 (OK) or -1 (ERROR) if unsuccessful
*
* Assumptions:
* Interrupts are disabled.
*
****************************************************************************/
void nxsem_add_holder(FAR sem_t *sem)
{
nxsem_add_holder_tcb(this_task(), sem);
}
/****************************************************************************
* Name: void nxsem_boost_priority(sem_t *sem)
*
* Description:
*
*
* Input Parameters:
* None
*
* Returned Value:
* 0 (OK) or -1 (ERROR) if unsuccessful
*
* Assumptions:
*
****************************************************************************/
void nxsem_boost_priority(FAR sem_t *sem)
{
FAR struct tcb_s *rtcb = this_task();
/* Boost the priority of every thread holding counts on this semaphore
* that are lower in priority than the new thread that is waiting for a
* count.
*/
#if CONFIG_SEM_PREALLOCHOLDERS > 0
nxsem_foreachholder(sem, nxsem_boostholderprio, rtcb);
#else
nxsem_boostholderprio(&sem->holder, sem, rtcb);
#endif
}
/****************************************************************************
* Name: nxsem_release_holder
*
* Description:
* Called from sem_post() after a thread releases one count on the
* semaphore.
*
* Input Parameters:
* sem - A reference to the semaphore being posted
*
* Returned Value:
* None
*
* Assumptions:
*
****************************************************************************/
void nxsem_release_holder(FAR sem_t *sem)
{
FAR struct tcb_s *rtcb = this_task();
uint8_t prioinherit = sem->flags & SEM_PRIO_MASK;
/* If priority inheritance is disabled for this thread or it is IDLE
* thread, then do not add the holder.
* If there are never holders of the semaphore, the priority
* inheritance is effectively disabled.
*/
if (!is_idle_task(rtcb) && prioinherit == SEM_PRIO_INHERIT)
{
FAR struct semholder_s *pholder;
DEBUGASSERT(!up_interrupt_context());
/* Find the container for this holder */
#if CONFIG_SEM_PREALLOCHOLDERS > 0
for (pholder = sem->hhead; pholder != NULL; pholder = pholder->flink)
{
DEBUGASSERT(pholder->counts > 0);
if (pholder->htcb == rtcb)
{
/* Decrement the counts on this holder -- the holder will be
* freed later in nxsem_restore_baseprio.
*/
pholder->counts--;
return;
}
}
/* The current task is not a holder */
DEBUGPANIC();
#else
pholder = &sem->holder;
DEBUGASSERT(pholder->htcb == rtcb);
nxsem_freeholder(sem, pholder);
#endif
}
}
/****************************************************************************
* Name: nxsem_restore_baseprio
*
* Description:
* This function is called after the current running task releases a
* count on the semaphore or an interrupt handler posts a new count. It
* will check if we need to drop the priority of any threads holding a
* count on the semaphore. Their priority could have been boosted while
* they held the count.
*
* Input Parameters:
* stcb - The TCB of the task that was just started (if any). If the
* post action caused a count to be given to another thread, then stcb
* is the TCB that received the count. Note, just because stcb received
* the count, it does not mean that it is higher priority than other
* threads.
* sem - A reference to the semaphore being posted.
* - If the semaphore count is <0 then there are still threads waiting
* for a count. stcb should be non-null and will be higher priority
* than all of the other threads still waiting.
* - If it is ==0 then stcb refers to the thread that got the last count;
* no other threads are waiting.
* - If it is >0 then there should be no threads waiting for counts and
* stcb should be null.
*
* Returned Value:
* None
*
* Assumptions:
* The scheduler is locked.
*
****************************************************************************/
void nxsem_restore_baseprio(FAR struct tcb_s *stcb, FAR sem_t *sem)
{
#if 0 /* DSA: sometimes crashes when Telnet calls external cmd (i.e. 'i2c') */
/* Check our assumptions */
DEBUGASSERT((sem->semcount > 0 && stcb == NULL) ||
(sem->semcount <= 0 && stcb != NULL));
#endif
DEBUGASSERT(!up_interrupt_context());
/* Perform the following actions only if a new thread was given a count.
* The thread that received the count should be the highest priority
* of all threads waiting for a count from the semaphore. So in that
* case, the priority of all holder threads should be dropped to the
* next highest pending priority.
*/
if (stcb != NULL)
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
/* The currently executed thread should be the lower priority
* thread that just posted the count and caused this action.
* However, we cannot drop the priority of the currently running
* thread -- because that will cause it to be suspended.
*
* So, do this in two passes. First, reprioritizing all holders
* except for the running thread.
*/
nxsem_foreachholder(sem, nxsem_restoreholderprio_others, stcb);
/* Now, find an reprioritize only the ready to run task */
nxsem_foreachholder(sem, nxsem_restoreholderprio_self, stcb);
#else
/* New owner is already the highest priority since the wait queue
* is priority-based, no need to adjust its priority, only restore
* the older owner when posted the count.
*/
nxsem_restore_priority(this_task());
#endif
}
else
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
/* Remove the holder from the list if it's counts is zero. */
nxsem_foreachholder(sem, nxsem_freecount0holder, NULL);
/* If there are no tasks waiting for available counts, then all holders
* should be at their base priority.
*/
#endif
#ifdef CONFIG_DEBUG_ASSERTIONS
nxsem_foreachholder(sem, nxsem_verifyholder, NULL);
#endif
}
}
/****************************************************************************
* Name: nxsem_canceled
*
* Description:
* Called from nxsem_wait_irq() after a thread that was waiting for a
* semaphore count was awakened because of a signal and the semaphore wait
* has been canceled. This function restores the correct thread priority
* of each holder of the semaphore.
*
* Input Parameters:
* sem - A reference to the semaphore no longer being waited for
*
* Returned Value:
* None
*
* Assumptions:
*
****************************************************************************/
void nxsem_canceled(FAR struct tcb_s *stcb, FAR sem_t *sem)
{
/* Check our assumptions */
DEBUGASSERT(sem->semcount <= 0);
/* Adjust the priority of every holder as necessary */
nxsem_foreachholder(sem, nxsem_restoreholderprio, stcb);
}
/****************************************************************************
* Name: sem_enumholders
*
* Description:
* Show information about threads currently waiting on this semaphore
*
* Input Parameters:
* sem - A reference to the semaphore
*
* Returned Value:
* None
*
* Assumptions:
*
****************************************************************************/
#if defined(CONFIG_DEBUG_FEATURES) && defined(CONFIG_SEM_PHDEBUG)
void sem_enumholders(FAR sem_t *sem)
{
#ifdef CONFIG_DEBUG_INFO
nxsem_foreachholder(sem, nxsem_dumpholder, NULL);
#endif
}
#endif
/****************************************************************************
* Name: nxsem_nfreeholders
*
* Description:
* Return the number of available holder containers. This is a good way
* to find out which threads are not calling sem_destroy.
*
* Input Parameters:
* sem - A reference to the semaphore
*
* Returned Value:
* The number of available holder containers
*
* Assumptions:
*
****************************************************************************/
#if defined(CONFIG_DEBUG_FEATURES) && defined(CONFIG_SEM_PHDEBUG)
int nxsem_nfreeholders(void)
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
FAR struct semholder_s *pholder;
int n;
for (pholder = g_freeholders, n = 0; pholder; pholder = pholder->flink)
{
n++;
}
return n;
#else
return 0;
#endif
}
#endif
/****************************************************************************
* Name: nxsem_release_all
*
* Description:
* Release all semaphore holders for the task.
*
* Input Parameters:
* htcb - TCB of the task
*
* Returned Value:
* None
*
* Assumptions:
*
****************************************************************************/
void nxsem_release_all(FAR struct tcb_s *htcb)
{
FAR struct semholder_s *pholder;
while ((pholder = htcb->holdsem) != NULL)
{
FAR sem_t *sem = pholder->sem;
nxsem_freeholder(sem, pholder);
/* Increment the count on the semaphore, to releases the count
* that was taken by sem_wait() or sem_post().
*/
sem->semcount++;
}
}
#endif /* CONFIG_PRIORITY_INHERITANCE */
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