rt_thread的IPC机制之互斥锁源码分析.doc

互斥锁是管理临界资源的一种有效手段。因为互斥锁是独占的，所以在一个时刻只允许一个线程占有互斥锁，利用这个性质来实现共享资源的互斥锁保护。任何时刻只允许一个线程获得互斥量对象，未能够获得互斥量对象的线程被挂起在该互斥量的等待线程队列上。1 互斥锁控制块cpp view plaincopyprint?1. /*2. *Mutualexclusion(mutex)structure3. */4. structrt_mutex5. 6. structrt_ipc_objectparent;/*inheritfromipc_object*/派生自IPC对象7. 8. rt_uint16_tvalue;/*valueofmutex*/此互斥锁的值9. 10. rt_uint8_toriginal_priority;/*priorityoflastthreadholdthemutex*/原始优先级,即此互斥锁拥有者线程的优先级11. rt_uint8_thold;/*numbersofthreadholdthemutex*/此互斥锁当前已被几个线程(同一线程)take的次数12. 13. structrt_thread*owner;/*currentownerofmutex*/此互斥锁的拥有者线程14. ;15. typedefstructrt_mutex*rt_mutex_t;/* * Mutual exclusion (mutex) structure */struct rt_mutex struct rt_ipc_object parent; /* inherit from ipc_object */派生自IPC对象 rt_uint16_t value; /* value of mutex */此互斥锁的值 rt_uint8_t original_priority; /* priority of last thread hold the mutex */原始优先级,即此互斥锁拥有者线程的优先级 rt_uint8_t hold; /* numbers of thread hold the mutex */此互斥锁当前已被几个线程(同一线程)take的次数 struct rt_thread *owner; /*parent.parent),RT_Object_Class_Mutex,name);/初始化互斥锁的内核对象 17. 18. /*initipcobject*/19. rt_ipc_object_init(&(mutex-parent);/初始化互斥锁的IPC对象 20. 21. mutex-value=1;/设置互斥锁值初始化为1 22. mutex-owner=RT_NULL;/初始化互斥锁当前没有拥有者 23. mutex-original_priority=0xFF;/初始化互斥锁原始优先级为255,即拥有者线程的优先级 24. mutex-hold=0;/初化为当前互斥锁的被take的次数为0(同一线程) 25. 26. /*setflag*/27. mutex-parent.parent.flag=flag;/设置互斥锁的内核对象标志 28. 29. returnRT_EOK;30. /* * This function will initialize a mutex and put it under control of resource * management. * * param mutex the mutex object * param name the name of mutex * param flag the flag of mutex * * return the operation status, RT_EOK on successful */rt_err_t rt_mutex_init(rt_mutex_t mutex, const char *name, rt_uint8_t flag) RT_ASSERT(mutex != RT_NULL); /* init object */ rt_object_init(&(mutex-parent.parent), RT_Object_Class_Mutex, name);/初始化互斥锁的内核对象 /* init ipc object */ rt_ipc_object_init(&(mutex-parent);/初始化互斥锁的IPC对象 mutex-value = 1;/设置互斥锁值初始化为1 mutex-owner = RT_NULL;/初始化互斥锁当前没有拥有者 mutex-original_priority = 0xFF;/初始化互斥锁原始优先级为255,即拥有者线程的优先级 mutex-hold = 0;/初化为当前互斥锁的被take的次数为0(同一线程) /* set flag */ mutex-parent.parent.flag = flag;/设置互斥锁的内核对象标志 return RT_EOK;注意互斥锁在初始化时其值value被初始化为1,即默认情况下其是可用的.在其被take之后value值减1变为0时才不可用.2.2 创建互斥锁cpp view plaincopyprint?1. /*2. *Thisfunctionwillcreateamutexfromsystemresource3. *4. *paramnamethenameofmutex5. *paramflagtheflagofmutex6. *7. *returnthecreatedmutex,RT_NULLonerrorhappen8. *9. *seert_mutex_init10. */11. rt_mutex_trt_mutex_create(constchar*name,rt_uint8_tflag)12. 13. structrt_mutex*mutex;14. 15. RT_DEBUG_NOT_IN_INTERRUPT;/确保此函数不是在ISR中使用 16. 17. /*allocateobject*/18. mutex=(rt_mutex_t)rt_object_allocate(RT_Object_Class_Mutex,name);/动态分配一个互斥锁 19. if(mutex=RT_NULL)20. returnmutex;21. 22. /*initipcobject*/23. rt_ipc_object_init(&(mutex-parent);/初始化此互斥锁的内核IPC对象 24. 25. mutex-value=1;/初始化互斥锁的值为1 26. mutex-owner=RT_NULL;/无拥有者 27. mutex-original_priority=0xFF;/互斥锁原始优先级为255 28. mutex-hold=0;/take此互斥锁的线程个数(同一线程)次数为0 29. 30. /*setflag*/31. mutex-parent.parent.flag=flag;/设置互斥锁内核对象标志 32. 33. returnmutex;34. /* * This function will create a mutex from system resource * * param name the name of mutex * param flag the flag of mutex * * return the created mutex, RT_NULL on error happen * * see rt_mutex_init */rt_mutex_t rt_mutex_create(const char *name, rt_uint8_t flag) struct rt_mutex *mutex; RT_DEBUG_NOT_IN_INTERRUPT;/确保此函数不是在ISR中使用 /* allocate object */ mutex = (rt_mutex_t)rt_object_allocate(RT_Object_Class_Mutex, name);/动态分配一个互斥锁 if (mutex = RT_NULL) return mutex; /* init ipc object */ rt_ipc_object_init(&(mutex-parent);/初始化此互斥锁的内核IPC对象 mutex-value = 1;/初始化互斥锁的值为1 mutex-owner = RT_NULL;/无拥有者 mutex-original_priority = 0xFF;/互斥锁原始优先级为255 mutex-hold = 0;/take此互斥锁的线程个数(同一线程)次数为0 /* set flag */ mutex-parent.parent.flag = flag;/设置互斥锁内核对象标志 return mutex;此函数与初始化类似,直接跳过.3 脱离或删除互斥锁3.1 脱离互斥锁cpp view plaincopyprint?1. /*2. *Thisfunctionwilldetachamutexfromresourcemanagement3. *4. *parammutexthemutexobject5. *6. *returntheoperationstatus,RT_EOKonsuccessful7. *8. *seert_mutex_delete9. */10. rt_err_trt_mutex_detach(rt_mutex_tmutex)11. 12. RT_ASSERT(mutex!=RT_NULL);13. 14. /*wakeupallsuspendthreads*/15. rt_ipc_list_resume_all(&(mutex-parent.suspend_thread);/唤醒所有挂起的线程 16. 17. /*detachsemaphoreobject*/18. rt_object_detach(&(mutex-parent.parent);/脱离互斥锁的内核对象 19. 20. returnRT_EOK;21. /* * This function will detach a mutex from resource management * * param mutex the mutex object * * return the operation status, RT_EOK on successful * * see rt_mutex_delete */rt_err_t rt_mutex_detach(rt_mutex_t mutex) RT_ASSERT(mutex != RT_NULL); /* wakeup all suspend threads */ rt_ipc_list_resume_all(&(mutex-parent.suspend_thread);/唤醒所有挂起的线程 /* detach semaphore object */ rt_object_detach(&(mutex-parent.parent);/脱离互斥锁的内核对象 return RT_EOK;脱离互斥锁只要是唤醒挂起的线程及脱离其内核对象,没有什么好说明的.3.2 删除互斥锁cpp view plaincopyprint?1. /*2. *Thisfunctionwilldeleteamutexobjectandreleasethememory3. *4. *parammutexthemutexobject5. *6. *returntheerrorcode7. *8. *seert_mutex_detach9. */10. rt_err_trt_mutex_delete(rt_mutex_tmutex)11. 12. RT_DEBUG_NOT_IN_INTERRUPT;/确保此函数不是在ISR中使用 13. 14. RT_ASSERT(mutex!=RT_NULL);15. 16. /*wakeupallsuspendthreads*/17. rt_ipc_list_resume_all(&(mutex-parent.suspend_thread);/唤醒所有挂起的线程 18. 19. /*deletesemaphoreobject*/20. rt_object_delete(&(mutex-parent.parent);/删除互斥锁的内核对象 21. 22. returnRT_EOK;23. /* * This function will delete a mutex object and release the memory * * param mutex the mutex object * * return the error code * * see rt_mutex_detach */rt_err_t rt_mutex_delete(rt_mutex_t mutex) RT_DEBUG_NOT_IN_INTERRUPT;/确保此函数不是在ISR中使用 RT_ASSERT(mutex != RT_NULL); /* wakeup all suspend threads */ rt_ipc_list_resume_all(&(mutex-parent.suspend_thread);/唤醒所有挂起的线程 /* delete semaphore object */ rt_object_delete(&(mutex-parent.parent);/删除互斥锁的内核对象 return RT_EOK;除了唤醒挂起的线程还需要删除其内核对象.3.3 获取互斥锁cpp view plaincopyprint?1. /*2. *Thisfunctionwilltakeamutex,ifthemutexisunavailable,the3. *threadshallwaitforaspecifiedtime.4. *5. *parammutexthemutexobject6. *paramtimethewaitingtime7. *8. *returntheerrorcode9. */10. rt_err_trt_mutex_take(rt_mutex_tmutex,rt_int32_ttime)11. 12. registerrt_base_ttemp;13. structrt_thread*thread;14. 15. /*thisfunctionmustnotbeusedininterrupteveniftime=0*/16. RT_DEBUG_NOT_IN_INTERRUPT;/确保此函数不是在ISR中使用 17. 18. RT_ASSERT(mutex!=RT_NULL);19. 20. /*disableinterrupt*/21. temp=rt_hw_interrupt_disable();/关中断 22. 23. /*getcurrentthread*/24. thread=rt_thread_self();/获取当前线程 25. 26. RT_OBJECT_HOOK_CALL(rt_object_trytake_hook,(&(mutex-parent.parent);27. 28. RT_DEBUG_LOG(RT_DEBUG_IPC,29. (mutex_take:currentthread%s,mutexvalue:%d,hold:%dn,30. thread-name,mutex-value,mutex-hold);31. 32. /*resetthreaderror*/33. thread-error=RT_EOK;/设置当前线程的错误标志为RT_EOK 34. 35. if(mutex-owner=thread)/如果当前互斥锁的拥有者就是当前线程,即当前线程重复take同一互斥锁,则当前互斥锁的take次数加1 36. 37. /*itsthesamethread*/38. mutex-hold+;39. 40. else/如果当前互斥锁的拥有者不是本身线程 41. 42. /*Thevalueofmutexis1ininitialstatus.Therefore,ifthe43. *valueisgreatthan0,itindicatesthemutexisavaible.44. */45. if(mutex-value0)/当前互斥锁的值大于0,则说明此互斥锁可用 46. 47. /*mutexisavailable*/48. mutex-value-;/将互斥锁的值减1 49. 50. /*setmutexownerandoriginalpriority*/51. mutex-owner=thread;/设置互斥锁的拥有者为当前线程 52. mutex-original_priority=thread-current_priority;/设置互斥锁的原始优先级为当前线程的优先级 53. mutex-hold+;/互斥锁被成功take,take次数加1 54. 55. else/如果当前互斥锁不可用 56. 57. /*nowaiting,returnwithtimeout*/58. if(time=0)/如果等待参数为0,则应立即返回错误 59. 60. /*seterrorastimeout*/61. thread-error=-RT_ETIMEOUT;/设置超时错误 62. 63. /*enableinterrupt*/64. rt_hw_interrupt_enable(temp);/开中断 65. 66. return-RT_ETIMEOUT;/返回超时错误 67. 68. else/如果时间参数不为0 69. 70. /*mutexisunavailable,pushtosuspendlist*/71. RT_DEBUG_LOG(RT_DEBUG_IPC,(mutex_take:suspendthread:%sn,72. thread-name);73. 74. /*changetheownerthreadpriorityofmutex*/75. if(thread-current_priorityowner-current_priority)/如果当前线程的优先级比互斥锁拥有者线程大的话(优先级值越小,优先级越高) 76. 77. /*changetheownerthreadpriority*/78. rt_thread_control(mutex-owner,/则修改当前互斥锁拥有者线程的优先级降为当前线程的优先级,如果不这么做的话,则如果拥有者线程永远不释放,则当前线程永远不可能获取此互斥锁,这样有可以会造成问题 79. RT_THREAD_CTRL_CHANGE_PRIORITY,/这样拥有者线程和当前线程优先级相同,系统采用时间片轮转方式,当前线程就有了获得互斥锁的可能了 80. &thread-current_priority);81. 82. 83. /*suspendcurrentthread*/84. rt_ipc_list_suspend(&(mutex-parent.suspend_thread),/挂起当前线程 85. thread,86. mutex-parent.parent.flag);87. 88. /*haswaitingtime,startthreadtimer*/89. if(time0)/如果时间参数大于0 90. 91. RT_DEBUG_LOG(RT_DEBUG_IPC,92. (mutex_take:startthetimerofthread:%sn,93. thread-name);94. 95. /*resetthetimeoutofthreadtimerandstartit*/96. rt_timer_control(&(thread-thread_timer),/设置定时器 97. RT_TIMER_CTRL_SET_TIME,98. &time);99. rt_timer_start(&(thread-thread_timer);/启动定时器 100. 101. 102. /*enableinterrupt*/103. rt_hw_interrupt_enable(temp);/开中断 104. 105. /*doschedule*/106. rt_schedule();/立即重新调度线程 107. 108. if(thread-error!=RT_EOK)/等待时间已到,但还是未成功获得互斥锁时,thread-error的值会被设为-RT_ETIMEOUT,见thread.c源文件中的rt_thread_timeout函数 109. 110. /*returnerror*/111. returnthread-error;112. 113. else/如果在另一线程执行rt_mutex_release函数唤醒此线程,则此线程在在处被唤醒时即已经获得互斥锁,这一过程中thread-error的值都未被修改,还是保持为RT_EOK 114. 115. /*themutexistakensuccessfully.*/116. /*disableinterrupt*/117. temp=rt_hw_interrupt_disable();/关中断 118. 119. 120. 121. 122. 123. /*enableinterrupt*/124. rt_hw_interrupt_enable(temp);/开中断 125. 126. RT_OBJECT_HOOK_CALL(rt_object_take_hook,(&(mutex-parent.parent);127. 128. returnRT_EOK;129. /* * This function will take a mutex, if the mutex is unavailable, the * thread shall wait for a specified time. * * param mutex the mutex object * param time the waiting time * * return the error code */rt_err_t rt_mutex_take(rt_mutex_t mutex, rt_int32_t time) register rt_base_t temp; struct rt_thread *thread; /* this function must not be used in interrupt even if time = 0 */ RT_DEBUG_NOT_IN_INTERRUPT;/确保此函数不是在ISR中使用 RT_ASSERT(mutex != RT_NULL); /* disable interrupt */ temp = rt_hw_interrupt_disable();/关中断 /* get current thread */ thread = rt_thread_self();/获取当前线程 RT_OBJECT_HOOK_CALL(rt_object_trytake_hook, (&(mutex-parent.parent); RT_DEBUG_LOG(RT_DEBUG_IPC, (mutex_take: current thread %s, mutex value: %d, hold: %dn, thread-name, mutex-value, mutex-hold); /* reset thread error */ thread-error = RT_EOK;/设置当前线程的错误标志为RT_EOK if (mutex-owner = thread)/如果当前互斥锁的拥有者就是当前线程,即当前线程重复take同一互斥锁,则当前互斥锁的take次数加1 /* its the same thread */ mutex-hold +; else/如果当前互斥锁的拥有者不是本身线程 /* The value of mutex is 1 in initial status. Therefore, if the * value is great than 0, it indicates the mutex is avaible. */ if (mutex-value 0)/当前互斥锁的值大于0,则说明此互斥锁可用 /* mutex is available */ mutex-value -;/将互斥锁的值减1 /* set mutex owner and original priority */ mutex-owner = thread;/设置互斥锁的拥有者为当前线程 mutex-original_priority = thread-current_priority;/设置互斥锁的原始优先级为当前线程的优先级 mutex-hold +;/互斥锁被成功take,take次数加1 else/如果当前互斥锁不可用 /* no waiting, return with timeout */ if (time = 0)/如果等待参数为0,则应立即返回错误 /* set error as timeout */ thread-error = -RT_ETIMEOUT;/设置超时错误 /* enable interrupt */ rt_hw_interrupt_enable(temp);/开中断 return -RT_ETIMEOUT;/返回超时错误 else/如果时间参数不为0 /* mutex is unavailable, push to suspend list */ RT_DEBUG_LOG(RT_DEBUG_IPC, (mutex_take: suspend thread: %sn, thread-name); /* change the owner thread priority of mutex */ if (thread-current_priority owner-current_priority)/如果当前线程的优先级比互斥锁拥有者线程大的话(优先级值越小,优先级越高) /* change the owner thread priority */ rt_thread_control(mutex-owner,/则修改当前互斥锁拥有者线程的优先级降为当前线程的优先级,如果不这么做的话,则如果拥有者线程永远不释放,则当前线程永远不可能获取此互斥锁,这样有可以会造成问题 RT_THREAD_CTRL_CHANGE_PRIORITY,/这样拥有者线程和当前线程优先级相同,系统采用时间片轮转方式,当前线程就有了获得互斥锁的可能了 &thread-current_priority); /* suspend current thread */ rt_ipc_list_suspend(&(mutex-parent.suspend_thread),/挂起当前线程 thread, mutex-parent.parent.flag); /* has waiting time, start thread timer */ if (time 0)/如果时间参数大于0 RT_DEBUG_LOG(RT_DEBUG_IPC, (mutex_take: start the timer of thread:%sn, thread-name); /* reset the timeout of thread timer and start it */ rt_timer_control(&(thread-thread_timer),/设置定时器 RT_TIMER_CTRL_SET_TIME, &time); rt_timer_start(&(thread-thread_timer);/启动定时器 /* enable interrupt */ rt_hw_interrupt_enable(temp);/开中断 /* do schedule