概述
取消一个线程要确保该线程能够释放其所持有的锁、分配的内存，使整个系统保持一致性。线程取消的途径有两种：异步取消和延时取消。
异步取消：被取消线程收到取消信号后，立即死亡。该线程缩持有的资源可能得不到释放，这是一种非安全的线程取消方式。
延时取消：系统默认取消方式，是一种比较安全的线程取消机制，被取消线程取消时，只是设置取消点(ptcbDel->TCB_bCancelRequest)为true，被取消线程继续运行，等到安全位置后进行取消操作。
取消点: 在使用延迟取消机制时，一个线程在可以被取消的地方定义取消点，当收到取消请求时，被取消的线程执行到取消点时退出，或者在一个取消点调用被阻塞时退出。
关键结构体
程序清单2.1 TCB结构体部分节选
typedef struct __lw_tcb {
...
??? LW_LIST_LINE????????? TCB_lineManage;????????? /? 内核管理用线表????????????? /
??? LW_LIST_RING????????? TCB_ringReady;?????????? /? 相同优先级就绪环??????????? /
???
??? LW_CLASS_WAKEUP_NODE? TCB_wunDelay;????? /? 等待节点??????????????????? /
#define TCB_ulDelay?????? TCB_wunDelay.WUN_ulCounter
...
#if (LW_CFG_EVENT_EN > 0) && (LW_CFG_MAX_EVENTS > 0)
??? LW_LIST_RING????????? TCB_ringEvent;????????? ???/? 事件等待队列表????????????? /
??? PLW_CLASS_EVENT?????? TCB_peventPtr;??????????? /? 等待事件指针????????????? ?/
??? PLW_LIST_RING??????? TCB_ppringPriorityQueue;????? /? 在 PRIORITY 队列位置???? */
??????????????????????????????????????????????? /? 由于删除线程时需要解等待链，/
?????????????????????????????????????????????? /? 这时需要确定队列位置??????? /
#endif
#if LW_CFG_COROUTINE_EN > 0
??? LW_CLASS_COROUTINE??? TCB_crcbOrigent;???????? /? 协程起源点????????????????? /
??? PLW_LIST_RING???????? TCB_pringCoroutineHeader;?? /? 协程首地址???????????????? /
#endif??????????????????????????????????????????? /? LW_CFG_COROUTINE_EN > 0???? /
...
??? volatile ULONG??????? TCB_ulCPUId;?????????? /? 如果正在运行, 表示运行 CPU? /
??? volatile BOOL???????? TCB_bIsCand;?????????? /? 是否在候选运行表中???????? ?/
#if LW_CFG_SMP_EN > 0
??? struct __lw_tcb????? TCB_ptcbWaitStatus;????????? /? 等待状态修改的目标线程????? */
??? PLW_LIST_LINE???????? TCB_plineStatusReqHeader;???? /? 等待修改本线程状态?????? /
??? LW_LIST_LINE????????? TCB_lineStatusPend;????????? /? 等待目标线程状态修改?? ????/
#endif?????????????????????????????????????????????? /? LW_CFG_SMP_EN????????????? /
...
??? PLW_EVENTSETNODE????? TCB_pesnPtr;????? /? 指向该线程等待????????????? /
...
#if LW_CFG_THREAD_CANCEL_EN > 0
??? BOOL????????????????? TCB_bCancelRequest;???? /? 取消请求??????????????????? /
??? INT?????????????????? TCB_iCancelState;???????? /? 取消状态??????????????????? /
??? INT?????????????????? TCB_iCancelType;????????? /? 取消类型??????????????????? /
#endif???????????????????????????????????????? /? LW_CFG_THREAD_CANCEL_EN???? /
...
#if LW_CFG_THREAD_DEL_EN > 0
??? struct __lw_tcb????? TCB_ptcbDeleteMe;?????? /? 要将本线程删除的 TCB??????? */
??? struct __lw_tcb????? TCB_ptcbDeleteWait;???????? /? 等待对方删除的 TCB????????? */
#endif???????????????????????????? ????????????????/? LW_CFG_THREAD_DEL_EN > 0??? /
??? UINT8???????????????? TCB_ucStackAutoAllocFlag;???? /? 堆栈是否有系统在堆中开辟?? /????????
??? PVOID???????????????? TCB_pvVProcessContext;?????? /? 进程上下文???????????????? /
...
} LW_CLASS_TCB;
程序清单2.2 等待队列
typedef union {
??? PLW_LIST_RING???????? WL_pringFifo;????????????????? /? 基于先入先出的等待队列?? /
??? PLW_LIST_RING???????? WL_pringPrio[__EVENT_Q_SIZE];? /? 基于优先级的等待队列?? /
} LW_UNION_WAITLIST;
typedef LW_UNION_WAITLIST *PLW_UNION_WAITLIST;
typedef struct {
??? LW_UNION_WAITLIST???? WQ_wlQ;??????????????? /? 等待队列??????????????????? /
??? UIN×××6??????????????? WQ_usNum;??????????????? /? 等待队列中的线程个数??????? /
} LW_CLASS_WAITQUEUE;
typedef LW_CLASS_WAITQUEUE *PLW_CLASS_WAITQUEUE;
程序清单2.3 事件集
typedef struct {???????????????????????????????????????????? /? 事件集??????????????????? /
??? LW_LIST_MONO???????? EVENTSET_monoResrcList;???? /? 空闲资源表?????????????? /
??? UINT8??????????????? EVENTSET_ucType;????????????? /? 类型????????????????????? /
??? PLW_LIST_LINE??????? EVENTSET_plineWaitList;??????? /? 指向第一个等待线程??????? /
??? ULONG??????????????? EVENTSET_ulEventSets;???????? /? 32 bit 事件位???????????? /
??? ULONG??????????????? EVENTSET_ulOption;?????????? /? 事件集选项??????????????? /
??? UIN×××6?????????????? EVENTSET_usIndex;???????????? /? 数组中的索引????????????? /
??? CHAR???????????????? EVENTSET_cEventSetName[LW_CFG_OBJECT_NAME_SIZE];
???????????????????????????????????????????????????????? /? 事件标志组名????????????? ?/
} LW_CLASS_EVENTSET;
typedef LW_CLASS_EVENTSET *PLW_CLASS_EVENTSET;
typedef struct {????????????????????????????????????????????? /? 事件集节点?????????????? /
??? LW_LIST_LINE???????? EVENTSETNODE_lineManage;???? /? 事件标志组管理表??????? /
???
??? PVOID???????? ???????EVENTSETNODE_ptcbMe;?????? /? 指向等待任务的TCB??????? /
??? PVOID??????????????? EVENTSETNODE_pesEventSet;?? /? 指向标志组??????????????? /
??? ULONG??????????????? EVENTSETNODE_ulEventSets;?? /? 标志组开始等待?????????? /
??? UINT8??????????????? EVENTSETNODE_ucWaitType;???? /? 等待类型???????????????? /
} LW_CLASS_EVENTSETNODE;
typedef LW_CLASS_EVENTSETNODE?? *PLW_CLASS_EVENTSETNODE;
typedef PLW_CLASS_EVENTSETNODE?? PLW_EVENTSETNODE;
流程
API_ThreadCancel函数流程：
? ? ? 图3.1 API_ThreadCancel函数
API_ThreadTestCancel函数流程：
图3.2 API_ThreadTestCancel函数
pthread_delete函数流程：
图3.3 pthread_delete函数
__threadDelete函数流程：
图3.4 __threadDelete函数
原文地址：http://blog.51cto.com/11620867/2178629