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incubator-nuttx/sched/sem_holder.c

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/****************************************************************************
* 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 <nuttx/config.h>
#include <semaphore.h>
#include <sched.h>
#include <assert.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 0
#endif
/****************************************************************************
* Private Type Declarations
****************************************************************************/
typedef int (*holderhandler_t)(FAR struct semholder_s *pholder, FAR sem_t *sem, FAR void *arg);
/****************************************************************************
* 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;
pholder->counts = 0;
}
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 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
}
/****************************************************************************
* Name: sem_foreachholder
****************************************************************************/
static int sem_foreachholder(FAR sem_t *sem, holderhandler_t handler, FAR void *arg)
{
FAR struct semholder_s *pholder = &sem->hlist;
#if CONFIG_SEM_PREALLOCHOLDERS > 0
FAR struct semholder_s *next;
#endif
int ret = 0;
#if CONFIG_SEM_PREALLOCHOLDERS > 0
for (; pholder && ret == 0; pholder = next)
#endif
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
/* In case this holder gets deleted */
next = pholder->flink;
#endif
/* The initial "built-in" container may hold a NULL holder */
if (pholder->holder)
{
/* Call the handler */
ret = handler(pholder, sem, arg);
}
}
return ret;
}
/****************************************************************************
* Name: sem_recoverholders
****************************************************************************/
static int sem_recoverholders(FAR struct semholder_s *pholder, FAR sem_t *sem, FAR void *arg)
{
sem_freeholder(sem, pholder);
return 0;
}
/****************************************************************************
* Name: sem_boostholderprio
****************************************************************************/
static int sem_boostholderprio(FAR struct semholder_s *pholder, FAR sem_t *sem, FAR void *arg)
{
FAR _TCB *htcb = (FAR _TCB *)pholder->holder;
FAR _TCB *rtcb = (FAR _TCB*)arg;
/* Make sure that the thread is still active. If it exited without releasing
* its counts, then that would be a bad thing. But we can take no real
* action because we don't know know that the program is doing. Perhaps its
* plan is to kill a thread, then destroy the semaphore.
*/
if (!sched_verifytcb(htcb))
{
sdbg("TCB 0x%08x is a stale handle, counts lost\n", htcb);
sem_freeholder(sem, pholder);
}
#if CONFIG_SEM_NNESTPRIO > 0
/* If the priority of the thread that is waiting for a count is greater than
* the base priority of the thread holding a count, then we may need to
* adjust the holder's priority now or later to that priority.
*/
else if (rtcb->sched_priority > htcb->base_priority)
{
/* If the new priority is greater than the current, possibly already
* boosted priority of the holder thread, then we will have to raise
* the holder's priority now.
*/
if (rtcb->sched_priority > htcb->sched_priority)
{
/* If the current priority has already been boosted, then add the
* boost priority to the list of restoration priorities. When the
* higher priority thread gets its count, then we need to revert
* to this saved priority, not to the base priority.
*/
if (htcb->sched_priority > htcb->base_priority)
{
/* Save the current, boosted priority */
if (htcb->npend_reprio < CONFIG_SEM_NNESTPRIO)
{
htcb->pend_reprios[htcb->npend_reprio] = htcb->sched_priority;
htcb->npend_reprio++;
}
else
{
sdbg("CONFIG_SEM_NNESTPRIO exceeded\n");
}
}
/* 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.
*/
(void)sched_setpriority(htcb, rtcb->sched_priority);
}
else
{
/* The new priority is above the base priority of the holder,
* but not as high as its current working priority. Just put it
* in the list of pending restoration priorities so that when the
* higher priority thread gets its count, we can revert to this
* saved priority and not to the base priority.
*/
htcb->pend_reprios[htcb->npend_reprio] = rtcb->sched_priority;
htcb->npend_reprio++;
}
}
#else
/* If the priority of the thread that is waiting for a count is less than
* of equal to the priority of the thread holding a count, then do nothing
* because the thread is already running at a sufficient priority.
*/
else 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_block_task() processing.
*/
(void)sched_setpriority(htcb, rtcb->sched_priority);
}
#endif
return 0;
}
/****************************************************************************
* Name: sem_verifyholder
****************************************************************************/
#ifdef CONFIG_DEBUG
static int sem_verifyholder(FAR struct semholder_s *pholder, FAR sem_t *sem, FAR void *arg)
{
// REMOVE ME
#if 0 // Need to revisit this, but these assumptions seem to be untrue -- OR there is a bug???
FAR _TCB *htcb = (FAR _TCB *)pholder->holder;
/* Called after a semaphore has been released (incremented), the semaphore
* could is non-negative, and there is no thread waiting for the count.
* In this case, the priority of the holder should not be boosted.
*/
#if CONFIG_SEM_NNESTPRIO > 0
DEBUGASSERT(htcb->npend_reprio == 0);
#endif
DEBUGASSERT(htcb->sched_priority == htcb->base_priority);
#endif
return 0;
}
#endif
/****************************************************************************
* Name: sem_dumpholder
****************************************************************************/
#if defined(CONFIG_DEBUG) && defined(CONFIG_SEM_PHDEBUG)
static int sem_dumpholder(FAR struct semholder_s *pholder, FAR sem_t *sem, FAR void *arg)
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
dbg(" %08x: %08x %08x %04x\n",
pholder, pholder->flink, pholder->holder, pholder->counts);
#else
dbg(" %08x: %08x %04x\n", pholder, pholder->holder, pholder->counts);
#endif
return 0;
}
#endif
/****************************************************************************
* Name: sem_restoreholderprio
****************************************************************************/
static int sem_restoreholderprio(FAR struct semholder_s *pholder, FAR sem_t *sem, FAR void *arg)
{
FAR _TCB *htcb = (FAR _TCB *)pholder->holder;
#if CONFIG_SEM_NNESTPRIO > 0
FAR _TCB *stcb = (FAR _TCB *)arg;
int rpriority;
int i;
int j;
#endif
/* Make sure that the thread is still active. If it exited without releasing
* its counts, then that would be a bad thing. But we can take no real
* action because we don't know know that the program is doing. Perhaps its
* plan is to kill a thread, then destroy the semaphore.
*/
if (!sched_verifytcb(htcb))
{
sdbg("TCB 0x%08x is a stale handle, counts lost\n", htcb);
sem_freeholder(sem, pholder);
}
/* Was the priority of this thread boosted? If so, then drop its priority
* back to the correct level.
*/
else if (htcb->sched_priority != htcb->base_priority)
{
#if CONFIG_SEM_NNESTPRIO > 0
/* Are there other, pending priority levels to revert to? */
if (htcb->npend_reprio < 1)
{
/* No... the thread has only been boosted once. Reset all priorities
* back to the base priority.
*/
DEBUGASSERT(htcb->sched_priority == stcb->sched_priority && htcb->npend_reprio == 0);
sched_reprioritize(htcb, htcb->base_priority);
}
/* There are multiple pending priority levels. The thread's "boosted"
* priority could greater than or equal to "stcb->sched_priority" (it could be
* greater if its priority we boosted becuase it also holds another semaphore.
*/
else if (htcb->sched_priority <= stcb->sched_priority)
{
/* The thread has been boosted to the same priority as the task
* that just received the count. We will simply reprioritized
* to the next highest priority that we have in rpriority.
*/
/* Find the highest pending priority and remove it from the list */
for (i = 1, j = 0; i < htcb->npend_reprio; i++)
{
if (htcb->pend_reprios[i] > htcb->pend_reprios[j])
{
j = i;
}
}
/* Remove the highest priority pending priority from the list */
rpriority = htcb->pend_reprios[j];
i = htcb->npend_reprio - 1;
if (i > 0)
{
htcb->pend_reprios[j] = htcb->pend_reprios[i];
}
htcb->npend_reprio = i;
/* And apply that priority to the thread (while retaining the base_priority) */
sched_setpriority(htcb, rpriority);
}
else
{
/* The thread has been boosted to a higher priority than the task. The
* pending priority should be in he list (unless it was lost because of
* of list overflow).
*
* Search the list for the matching priority.
*/
for (i = 0; i < htcb->npend_reprio; i++)
{
/* Does this pending priority match the priority of the thread
* that just received the count?
*/
if (htcb->pend_reprios[i] == stcb->sched_priority)
{
/* Yes, remove it from the list */
j = htcb->npend_reprio - 1;
if (j > 0)
{
htcb->pend_reprios[i] = htcb->pend_reprios[j];
}
htcb->npend_reprio = j;
break;
}
}
}
#else
/* There is no alternative restore priorities, drop the priority
* all the way back to the threads "base" priority.
*/
sched_reprioritize(htcb, htcb->base_priority);
#endif
}
return 0;
}
/****************************************************************************
* Name: sem_restoreholderprioA & B
****************************************************************************/
static int sem_restoreholderprioA(FAR struct semholder_s *pholder, FAR sem_t *sem, FAR void *arg)
{
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
if (pholder->holder != rtcb)
{
return sem_restoreholderprio(pholder, sem, arg);
}
return 0;
}
static int sem_restoreholderprioB(FAR struct semholder_s *pholder, FAR sem_t *sem, FAR void *arg)
{
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
if (pholder->holder == rtcb)
{
(void)sem_restoreholderprio(pholder, sem, arg);
return 1;
}
return 0;
}
/****************************************************************************
* 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)
{
#if CONFIG_SEM_PREALLOCHOLDERS > 0
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(FAR sem_t *sem)
{
/* 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.
* 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->hlist.holder || sem->hlist.flink)
{
sdbg("Semaphore destroyed with holders\n");
(void)sem_foreachholder(sem, sem_recoverholders, NULL);
}
#else
if (sem->hlist.holder)
{
sdbg("Semaphore destroyed with holder\n");
}
sem->hlist.holder = NULL;
#endif
}
/****************************************************************************
* 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(FAR 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(FAR sem_t *sem)
{
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
/* 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.
*/
(void)sem_foreachholder(sem, sem_boostholderprio, rtcb);
}
/****************************************************************************
* 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(FAR 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 -- the holder will be freed
* later in sem_restorebaseprio.
*/
pholder->counts--;
}
}
/****************************************************************************
* Function: sem_restorebaseprio
*
* Description:
* This function is called after the current running task releases a
* count on the semaphore. 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.
*
* 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 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.
*
* Return Value:
* 0 (OK) or -1 (ERROR) if unsuccessful
*
* Assumptions:
* The scheduler is locked.
*
****************************************************************************/
void sem_restorebaseprio(FAR _TCB *stcb, FAR sem_t *sem)
{
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
FAR struct semholder_s *pholder;
/* Check our assumptions */
DEBUGASSERT((sem->semcount > 0 && stcb == NULL) ||
(sem->semcount <= 0 && stcb != NULL));
/* Perfom the following actions only if a new thread was given a count. */
if (stcb)
{
/* The currently executed thread should be the low priority
* thread that just posted the count and caused this action.
* However, we cannot drop the priority of the currently running
* thread -- becuase that will cause it to be suspended.
*
* So, do this in two passes. First, reprioritizing all holders
* except for the running thread.
*/
(void)sem_foreachholder(sem, sem_restoreholderprioA, stcb);
/* Now, find an reprioritize only the ready to run task */
(void)sem_foreachholder(sem, sem_restoreholderprioB, stcb);
}
/* If there are no tasks waiting for available counts, then all holders
* should be at their base priority.
*/
#ifdef CONFIG_DEBUG
else
{
(void)sem_foreachholder(sem, sem_verifyholder, NULL);
}
#endif
/* In any case, the currently execuing task should have an entry in the
* list. Its counts were previously decremented; if it now holds no
* counts, then we need to remove it from the list of holders.
*/
pholder = sem_findholder(sem, rtcb);
if (pholder)
{
/* When no more counts are held, remove the holder from the list. The
* count was decremented in sem_releaseholder.
*/
if (pholder->counts <= 0)
{
sem_freeholder(sem, pholder);
}
}
}
/****************************************************************************
* Function: sem_canceled
*
* Description:
* Called from sem_post() after a thread that was waiting for a semaphore
* count was awakened because of a signal and the semaphore wait has been
* canceled.
*
* Parameters:
* sem - A reference to the semaphore no longer being waited for
*
* Return Value:
* None
*
* Assumptions:
*
****************************************************************************/
void sem_canceled(FAR sem_t *sem)
{
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
/* Check our assumptions */
DEBUGASSERT(sem->semcount <= 0);
/* Adjust the priority of every holder as necessary */
(void)sem_foreachholder(sem, sem_restoreholderprio, rtcb);
}
/****************************************************************************
* Function: sem_enumholders
*
* Description:
* Show information about threads currently waiting on this semaphore
*
* Parameters:
* sem - A reference to the semaphore
*
* Return Value:
* None
*
* Assumptions:
*
****************************************************************************/
#if defined(CONFIG_DEBUG) && defined(CONFIG_SEM_PHDEBUG)
void sem_enumholders(FAR sem_t *sem)
{
(void)sem_foreachholder(sem, sem_dumpholder, NULL);
}
#endif
/****************************************************************************
* Function: sem_nfreeholders
*
* Description:
* Return the number of available holder containers. This is a good way
* to find out which threads are not calling sem_destroy.
*
* Parameters:
* sem - A reference to the semaphore
*
* Return Value:
* The number of available holder containers
*
* Assumptions:
*
****************************************************************************/
#if defined(CONFIG_DEBUG) && defined(CONFIG_SEM_PHDEBUG)
int sem_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
#endif /* CONFIG_PRIORITY_INHERITANCE */
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