目录

引言

一.理论联立

1.死锁的概念和原因

2.死锁检测的基本思路

 

3.有向图在死锁检测中的应用

二.代码实现案例（我们会介绍部分重要接口解释）

1.我们定义一个线性表来存线程ID和锁ID

2.表中数据的查询接口

3.表中数据的删除接口

4.表中数据的添加接口

5.before_lock接口

6.afterlock接口

7.after_unlock接口

8.加锁和解锁的接口

9.检测死锁的接口

三.结果展示

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引言

死锁是指在计算机系统中，多个进程（或线程）因竞争资源而造成的一种僵局，若无外力作用，这些进程（或线程）都将无法向前推进

我们将基于多个线程和多个互斥锁来介绍死锁的长生

 

一.理论联立

1.死锁的概念和原因

①.死锁是操作系统和学术概念，指线程占用资源导致互相等待对方释放资源的情况。

②.死锁常见于多线程环境中，导致CPU占用率100%，出现死循环。

图中有线程A，线程B，和线程C 三个线程 它们各自拥有自己各自的资源的情况下 其中

线程A想占用线程B的资源

线程B 想占用线程C的资源

线程C想占用线程A的资源 

最后形成了一个环 最后导致了死锁

2.死锁检测的基本思路

①.死锁检测依赖于资源占用情况的检测，通过判断是否构成环来实现。

②.环的构成表示线程间形成了死锁。

 

3.有向图在死锁检测中的应用

①.有向图是否成环的问题是死锁检测的底层算法。

②.通过有向图来判断是否构成环，从而检测死锁。

③.有向图的构建通过节点和边来表示线程和资源的关系。

④.环的检测通过深度优先搜索（DFS）来实现。

 

 

 

二.代码实现案例（我们会介绍部分重要接口解释）

#include<stdio.h>
#include<pthread.h>
#include<unistd.h>
#define _GNU_SOURCE
#include <dlfcn.h>
#include<stdlib.h>#define MAX		100typedef unsigned long int uint64;struct rela_node{pthread_mutex_t *mtx;pthread_t thid;
};struct rela_node rela_table[MAX]={0};//search
pthread_t search_rela_table(pthread_mutex_t*mtx){int i = 0;for(i;i<MAX;i++){if(mtx==rela_table[i].mtx){return rela_table[i].thid;}}return 0;
}//dele
int dele_rela_table(pthread_t tid,pthread_mutex_t *mtx){int i =0;for(i;i<MAX;i++){if((rela_table[i].thid==tid)&&(rela_table[i].mtx==mtx)){rela_table[i].thid=0;rela_table[i].mtx=NULL;return 0;}}return -1;
}//add
int add_rela_table(pthread_t tid,pthread_mutex_t *mtx){int i =0;for(i;i<MAX;i++){if((rela_table[i].thid==0)&&(rela_table[i].mtx==NULL)){rela_table[i].thid=tid;rela_table[i].mtx=mtx;return 0;}}return -1;
}#if 1  
//有向图
enum Type {PROCESS, RESOURCE};struct source_type {uint64 id;enum Type type;uint64 lock_id;int degress;
};struct vertex {struct source_type s;struct vertex *next;};struct task_graph {struct vertex list[MAX];int num;struct source_type locklist[MAX];int lockidx; //pthread_mutex_t mutex;
};struct task_graph *tg = NULL;
int path[MAX+1];
int visited[MAX];
int k = 0;
int deadlock = 0;struct vertex *create_vertex(struct source_type type) {struct vertex *tex = (struct vertex *)malloc(sizeof(struct vertex ));tex->s = type;tex->next = NULL;return tex;}int search_vertex(struct source_type type) {int i = 0;for (i = 0;i < tg->num;i ++) {if (tg->list[i].s.type == type.type && tg->list[i].s.id == type.id) {return i;}}return -1;
}void add_vertex(struct source_type type) {if (search_vertex(type) == -1) {tg->list[tg->num].s = type;tg->list[tg->num].next = NULL;tg->num ++;}}int add_edge(struct source_type from, struct source_type to) {add_vertex(from);add_vertex(to);struct vertex *v = &(tg->list[search_vertex(from)]);while (v->next != NULL) {v = v->next;}v->next = create_vertex(to);}int verify_edge(struct source_type i, struct source_type j) {if (tg->num == 0) return 0;int idx = search_vertex(i);if (idx == -1) {return 0;}struct vertex *v = &(tg->list[idx]);while (v != NULL) {if (v->s.id == j.id) return 1;v = v->next;}return 0;}int remove_edge(struct source_type from, struct source_type to) {int idxi = search_vertex(from);int idxj = search_vertex(to);if (idxi != -1 && idxj != -1) {struct vertex *v = &tg->list[idxi];struct vertex *remove;while (v->next != NULL) {if (v->next->s.id == to.id) {remove = v->next;v->next = v->next->next;free(remove);break;}v = v->next;}}}void print_deadlock(void) {int i = 0;printf("cycle : ");for (i = 0;i < k-1;i ++) {printf("%ld --> ", tg->list[path[i]].s.id);}printf("%ld\n", tg->list[path[i]].s.id);}int DFS(int idx) {struct vertex *ver = &tg->list[idx];if (visited[idx] == 1) {path[k++] = idx;print_deadlock();deadlock = 1;return 0;}visited[idx] = 1;path[k++] = idx;while (ver->next != NULL) {DFS(search_vertex(ver->next->s));k --;ver = ver->next;}return 1;}int search_for_cycle(int idx) {struct vertex *ver = &tg->list[idx];visited[idx] = 1;k = 0;path[k++] = idx;while (ver->next != NULL) {int i = 0;for (i = 0;i < tg->num;i ++) {if (i == idx) continue;visited[i] = 0;}for (i = 1;i <= MAX;i ++) {path[i] = -1;}k = 1;DFS(search_vertex(ver->next->s));ver = ver->next;}}int init_graph(void){tg=(struct task_graph*)malloc(sizeof(struct task_graph));tg->num=0;
}#endifvoid before_lock(pthread_t tid,pthread_mutex_t*mtx){pthread_t otherid=search_rela_table(mtx);if(otherid!=0){//mtx有线程在占用struct source_type from;from.id=tid;from.type=PROCESS;struct source_type to;to.id=otherid;to.type=PROCESS;add_edge(from,to);}}//如果走到after_lock 则表明mtx没有被线程占用 把之前的边删除 然后我们占用该mtx
void after_lock(pthread_t tid,pthread_mutex_t*mtx){pthread_t otherid=search_rela_table(mtx);if(otherid!=0){//删除旧边struct source_type from;from.id=tid;from.type=PROCESS;struct source_type to;to.id=otherid;to.type=PROCESS;if(verify_edge(from,to)){remove_edge(from,to);}}//mtx无线程在占用 则占我们占用add_rela_table(tid,mtx);
}
void after_unlock(pthread_t tid,pthread_mutex_t*mtx){dele_rela_table(tid,mtx);//有小问题 这个死锁工具可能只能检测一次 如果存在解锁情况 可能会导致after_lock mtx找不到旧线程id
}//检测死锁
void check_dead_lock(void){int i =0;for(i;i<tg->num;i++){search_for_cycle(i);}
}static void *thread_routine(void*arg){while(1){sleep(5);check_dead_lock();}
}
void start_check(void) {pthread_t tid;pthread_create(&tid, NULL, thread_routine, NULL);}#if 1  //hook
typedef int (*pthread_mutex_lock_t)(pthread_mutex_t*mtx);
pthread_mutex_lock_t pthread_mutex_lock_f=NULL;typedef int (*pthread_mutex_unlock_t)(pthread_mutex_t*mtx);
pthread_mutex_unlock_t pthread_mutex_unlock_f=NULL;typedef int (*pthread_create_t)(pthread_t *restrict thread, const pthread_attr_t *restrict attr,void *(*start_routine)(void *), void *restrict arg);
pthread_create_t pthread_create_f = NULL;int pthread_mutex_lock(pthread_mutex_t*mtx){// printf("before pthread_mutex_lock%ld,%p \n",pthread_self(),mtx);pthread_t selfid = pthread_self();before_lock(selfid, mtx);pthread_mutex_lock_f(mtx);// printf("after pthread_mutex_lock\n");after_lock(selfid,mtx);
}int pthread_mutex_unlock(pthread_mutex_t*mtx){pthread_t selfid = pthread_self();pthread_mutex_unlock_f(mtx);after_unlock(selfid,mtx);// printf("after pthread_mutex_unlock%ld,%p \n",pthread_self(),mtx);}int pthread_create(pthread_t *restrict thread, const pthread_attr_t *restrict attr,void *(*start_routine)(void *), void *restrict arg) {pthread_create_f(thread,attr,start_routine,arg);struct source_type v1;v1.id=*thread;v1.type=PROCESS;add_vertex(v1);
}void init_hook(void){if(!pthread_mutex_lock_f){pthread_mutex_lock_f = dlsym(RTLD_NEXT,"pthread_mutex_lock");}if(!pthread_mutex_unlock_f){pthread_mutex_unlock_f = dlsym(RTLD_NEXT,"pthread_mutex_unlock");}if (!pthread_create_f) {pthread_create_f = dlsym(RTLD_NEXT, "pthread_create");}}
#endif#if 1//debug
pthread_mutex_t mtx1 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mtx2 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mtx3 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mtx4 = PTHREAD_MUTEX_INITIALIZER;void * t1_cb(void*arg){printf("pid1=%ld\n",pthread_self());pthread_mutex_lock(&mtx1);sleep(1);pthread_mutex_lock(&mtx2);pthread_mutex_unlock(&mtx2);pthread_mutex_unlock(&mtx1);}
void * t2_cb(void*arg){printf("pid2=%ld\n",pthread_self());pthread_mutex_lock(&mtx2);sleep(1);pthread_mutex_lock(&mtx3);pthread_mutex_unlock(&mtx3);pthread_mutex_unlock(&mtx2);}void * t3_cb(void*arg){printf("pid3=%ld\n",pthread_self());pthread_mutex_lock(&mtx3);sleep(1);pthread_mutex_lock(&mtx4);pthread_mutex_unlock(&mtx4);pthread_mutex_unlock(&mtx3);
}void * t4_cb(void*arg){printf("pid4=%ld\n",pthread_self());pthread_mutex_lock(&mtx4);sleep(1);pthread_mutex_lock(&mtx1);pthread_mutex_unlock(&mtx1);pthread_mutex_unlock(&mtx4);
}
int main(){init_graph();//有向图的初始化init_hook();//hook函数的初始化pthread_t t1,t2,t3,t4;start_check();//开始检测死锁pthread_create(&t1,NULL,t1_cb,NULL);pthread_create(&t2,NULL,t2_cb,NULL);pthread_create(&t3,NULL,t3_cb,NULL);pthread_create(&t4,NULL,t4_cb,NULL);pthread_join(t1,NULL);pthread_join(t2,NULL);pthread_join(t3,NULL);pthread_join(t4,NULL);printf("complete\n");
}
#endif

具体代码接口的实现

1.我们定义一个线性表来存线程ID和锁ID

typedef unsigned long int uint64;struct rela_node{pthread_mutex_t *mtx;pthread_t thid;
};struct rela_node rela_table[MAX]={0};

2.表中数据的查询接口

//search
pthread_t search_rela_table(pthread_mutex_t*mtx){int i = 0;for(i;i<MAX;i++){if(mtx==rela_table[i].mtx){return rela_table[i].thid;}}return 0;
}

 

3.表中数据的删除接口

//dele
int dele_rela_table(pthread_t tid,pthread_mutex_t *mtx){int i =0;for(i;i<MAX;i++){if((rela_table[i].thid==tid)&&(rela_table[i].mtx==mtx)){rela_table[i].thid=0;rela_table[i].mtx=NULL;return 0;}}return -1;
}

4.表中数据的添加接口

//add
int add_rela_table(pthread_t tid,pthread_mutex_t *mtx){int i =0;for(i;i<MAX;i++){if((rela_table[i].thid==0)&&(rela_table[i].mtx==NULL)){rela_table[i].thid=tid;rela_table[i].mtx=mtx;return 0;}}return -1;
}

 

5.before_lock接口

void before_lock(pthread_t tid,pthread_mutex_t*mtx){pthread_t otherid=search_rela_table(mtx);if(otherid!=0){//mtx有线程在占用struct source_type from;from.id=tid;from.type=PROCESS;struct source_type to;to.id=otherid;to.type=PROCESS;add_edge(from,to);}}

我们传入当前线程id和锁

我们先对锁进行判断是否有线程在占用 如果有线程在占用我们则和该线程建立一条边

6.afterlock接口

//如果走到after_lock 则表明mtx没有被线程占用 把之前的边删除 然后我们占用该mtx
void after_lock(pthread_t tid,pthread_mutex_t*mtx){pthread_t otherid=search_rela_table(mtx);if(otherid!=0){//删除旧边struct source_type from;from.id=tid;from.type=PROCESS;struct source_type to;to.id=otherid;to.type=PROCESS;if(verify_edge(from,to)){remove_edge(from,to);}}//mtx无线程在占用 则占我们占用add_rela_table(tid,mtx);
}

我们要先判断该锁之前是否和其他线程建立边 如果有我们就删除旧边 然后占用该把锁

7.after_unlock接口

void after_unlock(pthread_t tid,pthread_mutex_t*mtx){dele_rela_table(tid,mtx);//有小问题 这个死锁工具可能只能检测一次 如果存在解锁情况 可能会导致after_lock mtx找不到旧线程id
}

8.加锁和解锁的接口

int pthread_mutex_lock(pthread_mutex_t*mtx){// printf("before pthread_mutex_lock%ld,%p \n",pthread_self(),mtx);pthread_t selfid = pthread_self();before_lock(selfid, mtx);pthread_mutex_lock_f(mtx);// printf("after pthread_mutex_lock\n");after_lock(selfid,mtx);
}int pthread_mutex_unlock(pthread_mutex_t*mtx){pthread_t selfid = pthread_self();pthread_mutex_unlock_f(mtx);after_unlock(selfid,mtx);// printf("after pthread_mutex_unlock%ld,%p \n",pthread_self(),mtx);}

9.检测死锁的接口

//检测死锁
void check_dead_lock(void){int i =0;for(i;i<tg->num;i++){search_for_cycle(i);}
}static void *thread_routine(void*arg){while(1){sleep(5);check_dead_lock();}
}
void start_check(void) {pthread_t tid;pthread_create(&tid, NULL, thread_routine, NULL);}

 

三.结果展示