multithreading - threads safe linked list fine grained in C -

i'm implementing linked list fine grained locking, meaning lock in every node.

when i'm adding new node, want pass 2 arguments: key , value. how can make sure each node has different lock? lock implemented pthread_mutex_t.

this implementation add:

int setos_add(int key, void* value) { volatile setos_node* node = head; volatile setos_node* prev;  pthread_mutex_t new_mutex;  //wrong: put same lock  //lock head node if(pthread_mutex_lock(&(node->mutex)) == 0){     printf("failed locking\n");     exit(1); }  // go through nodes until key of "node" exceeds "key" // new node should between "prev" , "node" while ((node != null) && (node->key < key)) {     prev = node;  //already locked     node = node->next;     //locking 2 nodes each time     if (node != null){         if(pthread_mutex_lock(&(node->mutex)) == 0){             printf("failed locking\n");             exit(1);         }     }     if (node -> key < key){  //else: need preve staying locked       insertions         if (pthread_mutex_unlock(&(prev->mutex)) != 0){             printf("failed unlocking\n");             exit(1);         }     } }  // if node same our key - key in list if ((node != null) && (node->key == key)){      if (node != null){  //not end of list         if (pthread_mutex_unlock(&(node->mutex)) != 0){             printf("failed unlocking\n");             exit(1);         }     }      if (prev != null){ //not begining of list         if (pthread_mutex_unlock(&(prev->mutex)) != 0){             printf("failed unlocking\n");             exit(1);         }     }     return 0; }  // allocate new node , initialize setos_node* new_node = (setos_node*) malloc(sizeof(setos_node)); new_node->key = key; new_node->value = value; new_node->mutex = new_mutex;  //to change if(pthread_mutex_init(&(new_node-> mutex), null) != 0){     printf("failed init mutex");     exit(1); }   // place node list new_node->next = node; prev->next = new_node;  if (node != null){ //not end of list     if (pthread_mutex_unlock(&(node->mutex)) != 0){         printf("failed unlocking\n");         exit(1);     } }  if (prev != null){ //not begining of list     if (pthread_mutex_unlock(&(prev->mutex)) != 0){         printf("failed unlocking\n");         exit(1);      } }  return 1; } 

you can see in third line i'm defining pthread_mutex_t node. doing so, each new node have same pthread_mutex_t?

how can right?

yes same mutex.

you can malloc new mutex element each time need new mutex :

malloc(sizeof(pthread_mutex_t)))

an intialize :

pthread_mutex_init(m, null)