/* ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010, 2011 Giovanni Di Sirio. This file is part of ChibiOS/RT. ChibiOS/RT is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. ChibiOS/RT is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . */ /** * @file chmtx.c * @brief Mutexes code. * * @addtogroup mutexes * @details Mutexes related APIs and services. * *

Operation mode

* A mutex is a threads synchronization object that can be in two * distinct states: * - Not owned (unlocked). * - Owned by a thread (locked). * . * Operations defined for mutexes: * - Lock: The mutex is checked, if the mutex is not owned by * some other thread then it is associated to the locking thread * else the thread is queued on the mutex in a list ordered by * priority. * - Unlock: The mutex is released by the owner and the highest * priority thread waiting in the queue, if any, is resumed and made * owner of the mutex. * . *

Constraints

* In ChibiOS/RT the Unlock operations are always performed in * lock-reverse order. The unlock API does not even have a parameter, * the mutex to unlock is selected from an internal, per-thread, stack * of owned mutexes. This both improves the performance and is * required for an efficient implementation of the priority * inheritance mechanism. * *

The priority inversion problem

* The mutexes in ChibiOS/RT implements the full priority * inheritance mechanism in order handle the priority inversion * problem.
* When a thread is queued on a mutex, any thread, directly or * indirectly, holding the mutex gains the same priority of the * waiting thread (if their priority was not already equal or higher). * The mechanism works with any number of nested mutexes and any * number of involved threads. The algorithm complexity (worst case) * is N with N equal to the number of nested mutexes. * @pre In order to use the mutex APIs the @p CH_USE_MUTEXES option * must be enabled in @p chconf.h. * @post Enabling mutexes requires 5-12 (depending on the architecture) * extra bytes in the @p Thread structure. * @{ */ #include "ch.h" #if CH_USE_MUTEXES || defined(__DOXYGEN__) /** * @brief Initializes s @p Mutex structure. * * @param[out] mp pointer to a @p Mutex structure * * @init */ void chMtxInit(Mutex *mp) { chDbgCheck(mp != NULL, "chMtxInit"); queue_init(&mp->m_queue); mp->m_owner = NULL; } /** * @brief Locks the specified mutex. * @post The mutex is locked and inserted in the per-thread stack of owned * mutexes. * * @param[in] mp pointer to the @p Mutex structure * * @api */ void chMtxLock(Mutex *mp) { chSysLock(); chMtxLockS(mp); chSysUnlock(); } /** * @brief Locks the specified mutex. * @post The mutex is locked and inserted in the per-thread stack of owned * mutexes. * * @param[in] mp pointer to the @p Mutex structure * * @sclass */ void chMtxLockS(Mutex *mp) { Thread *ctp = currp; chDbgCheck(mp != NULL, "chMtxLockS"); /* Ia the mutex already locked? */ if (mp->m_owner != NULL) { /* Priority inheritance protocol; explores the thread-mutex dependencies boosting the priority of all the affected threads to equal the priority of the running thread requesting the mutex.*/ Thread *tp = mp->m_owner; /* Does the running thread have higher priority than the mutex ownning thread? */ while (tp->p_prio < ctp->p_prio) { /* Make priority of thread tp match the running thread's priority.*/ tp->p_prio = ctp->p_prio; /* The following states need priority queues reordering.*/ switch (tp->p_state) { case THD_STATE_WTMTX: /* Re-enqueues the mutex owner with its new priority.*/ prio_insert(dequeue(tp), (ThreadsQueue *)tp->p_u.wtobjp); tp = ((Mutex *)tp->p_u.wtobjp)->m_owner; continue; #if CH_USE_CONDVARS | CH_USE_SEMAPHORES_PRIORITY | CH_USE_MESSAGES_PRIORITY #if CH_USE_CONDVARS case THD_STATE_WTCOND: #endif #if CH_USE_SEMAPHORES_PRIORITY case THD_STATE_WTSEM: #endif #if CH_USE_MESSAGES_PRIORITY case THD_STATE_SNDMSGQ: #endif /* Re-enqueues tp with its new priority on the queue.*/ prio_insert(dequeue(tp), (ThreadsQueue *)tp->p_u.wtobjp); break; #endif case THD_STATE_READY: #if CH_DBG_ENABLE_ASSERTS /* Prevents an assertion in chSchReadyI().*/ tp->p_state = THD_STATE_CURRENT; #endif /* Re-enqueues tp with its new priority on the ready list.*/ chSchReadyI(dequeue(tp)); } break; } /* Sleep on the mutex.*/ prio_insert(ctp, &mp->m_queue); ctp->p_u.wtobjp = mp; chSchGoSleepS(THD_STATE_WTMTX); /* It is assumed that the thread performing the unlock operation assigns the mutex to this thread.*/ chDbgAssert(mp->m_owner == ctp, "chMtxLockS(), #1", "not owner"); chDbgAssert(ctp->p_mtxlist == mp, "chMtxLockS(), #2", "not owned"); } else { /* It was not owned, inserted in the owned mutexes list.*/ mp->m_owner = ctp; mp->m_next = ctp->p_mtxlist; ctp->p_mtxlist = mp; } } /** * @brief Tries to lock a mutex. * @details This function attempts to lock a mutex, if the mutex is already * locked by another thread then the function exits without waiting. * @post The mutex is locked and inserted in the per-thread stack of owned * mutexes. * @note This function does not have any overhead related to the * priority inheritance mechanism because it does not try to * enter a sleep state. * * @param[in] mp pointer to the @p Mutex structure * @return The operation status. * @retval TRUE if the mutex has been successfully acquired * @retval FALSE if the lock attempt failed. * * @api */ bool_t chMtxTryLock(Mutex *mp) { bool_t b; chSysLock(); b = chMtxTryLockS(mp); chSysUnlock(); return b; } /** * @brief Tries to lock a mutex. * @details This function attempts to lock a mutex, if the mutex is already * taken by another thread then the function exits without waiting. * @post The mutex is locked and inserted in the per-thread stack of owned * mutexes. * @note This function does not have any overhead related to the * priority inheritance mechanism because it does not try to * enter a sleep state. * * @param[in] mp pointer to the @p Mutex structure * @return The operation status. * @retval TRUE if the mutex has been successfully acquired * @retval FALSE if the lock attempt failed. * * @sclass */ bool_t chMtxTryLockS(Mutex *mp) { chDbgCheck(mp != NULL, "chMtxTryLockS"); if (mp->m_owner != NULL) return FALSE; mp->m_owner = currp; mp->m_next = currp->p_mtxlist; currp->p_mtxlist = mp; return TRUE; } /** * @brief Unlocks the next owned mutex in reverse lock order. * @pre The invoking thread must have at least one owned mutex. * @post The mutex is unlocked and removed from the per-thread stack of * owned mutexes. * * @return A pointer to the unlocked mutex. * * @api */ Mutex *chMtxUnlock(void) { Thread *ctp = currp; Mutex *ump, *mp; chSysLock(); chDbgAssert(ctp->p_mtxlist != NULL, "chMtxUnlock(), #1", "owned mutexes list empty"); chDbgAssert(ctp->p_mtxlist->m_owner == ctp, "chMtxUnlock(), #2", "ownership failure"); /* Removes the top Mutex from the Threads's owned mutexes list and matk it as not owned.*/ ump = ctp->p_mtxlist; ctp->p_mtxlist = ump->m_next; /* If a thread is waiting on the mutex then the fun part begins.*/ if (chMtxQueueNotEmptyS(ump)) { Thread *tp; /* Recalculates the optimal thread priority by scanning the owned mutexes list.*/ tprio_t newprio = ctp->p_realprio; mp = ctp->p_mtxlist; while (mp != NULL) { /* If the highest priority thread waiting in the mutexes list has a greater priority than the current thread base priority then the final priority will have at least that priority.*/ if (chMtxQueueNotEmptyS(mp) && (mp->m_queue.p_next->p_prio > newprio)) newprio = mp->m_queue.p_next->p_prio; mp = mp->m_next; } /* Assigns to the current thread the highest priority among all the waiting threads.*/ ctp->p_prio = newprio; /* Awakens the highest priority thread waiting for the unlocked mutex and assigns the mutex to it.*/ tp = fifo_remove(&ump->m_queue); ump->m_owner = tp; ump->m_next = tp->p_mtxlist; tp->p_mtxlist = ump; chSchWakeupS(tp, RDY_OK); } else ump->m_owner = NULL; chSysUnlock(); return ump; } /** * @brief Unlocks the next owned mutex in reverse lock order. * @pre The invoking thread must have at least one owned mutex. * @post The mutex is unlocked and removed from the per-thread stack of * owned mutexes. * @post This function does not reschedule so a call to a rescheduling * function must be performed before unlocking the kernel. * * @return A pointer to the unlocked mutex. * * @sclass */ Mutex *chMtxUnlockS(void) { Thread *ctp = currp; Mutex *ump, *mp; chDbgAssert(ctp->p_mtxlist != NULL, "chMtxUnlockS(), #1", "owned mutexes list empty"); chDbgAssert(ctp->p_mtxlist->m_owner == ctp, "chMtxUnlockS(), #2", "ownership failure"); /* Removes the top Mutex from the owned mutexes list and marks it as not owned.*/ ump = ctp->p_mtxlist; ctp->p_mtxlist = ump->m_next; /* If a thread is waiting on the mutex then the fun part begins.*/ if (chMtxQueueNotEmptyS(ump)) { Thread *tp; /* Recalculates the optimal thread priority by scanning the owned mutexes list.*/ tprio_t newprio = ctp->p_realprio; mp = ctp->p_mtxlist; while (mp != NULL) { /* If the highest priority thread waiting in the mutexes list has a greater priority than the current thread base priority then the final priority will have at least that priority.*/ if (chMtxQueueNotEmptyS(mp) && (mp->m_queue.p_next->p_prio > newprio)) newprio = mp->m_queue.p_next->p_prio; mp = mp->m_next; } ctp->p_prio = newprio; /* Awakens the highest priority thread waiting for the unlocked mutex and assigns the mutex to it.*/ tp = fifo_remove(&ump->m_queue); ump->m_owner = tp; ump->m_next = tp->p_mtxlist; tp->p_mtxlist = ump; chSchReadyI(tp); } else ump->m_owner = NULL; return ump; } /** * @brief Unlocks all the mutexes owned by the invoking thread. * @post The stack of owned mutexes is emptied and all the found * mutexes are unlocked. * @note This function is MUCH MORE efficient than releasing the * mutexes one by one and not just because the call overhead, * this function does not have any overhead related to the priority * inheritance mechanism. * * @api */ void chMtxUnlockAll(void) { Thread *ctp = currp; chSysLock(); if (ctp->p_mtxlist != NULL) { do { Mutex *ump = ctp->p_mtxlist; ctp->p_mtxlist = ump->m_next; if (chMtxQueueNotEmptyS(ump)) { Thread *tp = fifo_remove(&ump->m_queue); ump->m_owner = tp; ump->m_next = tp->p_mtxlist; tp->p_mtxlist = ump; chSchReadyI(tp); } else ump->m_owner = NULL; } while (ctp->p_mtxlist != NULL); ctp->p_prio = ctp->p_realprio; chSchRescheduleS(); } chSysUnlock(); } #endif /* CH_USE_MUTEXES */ /** @} */