c - Close a socket from the main thread -

i'm implementing p2p file transfer peer , tracker. tracker keeps track of peers , files, , peer connects peer when wanting download file , accepts requests other peers download 1 of files. this, peer acting both client , server other peers, , client tracker. so, using threads , have server process in 1 thread, client process in another, , 1 connecting tracker in main thread. when peer chooses exit, want close server process ie: process in separate server thread. tried making global variable containing file descriptor can close when client exits, giving me error after exit.

here peer code:

if want know how stop other threads main thread here 1 method. create struct let's call thread_state_t has flag tells threads stop, call active example. in thread check in loop value , whatever need based on state.

in simple case this

#include <stdio.h> #include <pthread.h>  typedef struct {     int active; } thread_state_t;  void* t1(void* arg) {     thread_state_t* state = (thread_state_t*) arg;     while(state->active > 0) {         // work     }     return null; }  int main() {     pthread_t tid;     thread_state_t state1;     state1.active = 1;      pthread_create(&tid, null, t1, (void*)&state1);      // ...     state1.active = 0;     // ...      pthread_join(tid, null);      return 0; } 

however example show main idea. in real implementation need make active variable or whole thread_state_t object thread safe (use mutex example).

to make thread safe can use add mutex state object

typedef struct {     pthread_mutex_t mutex;     int active; } thread_state_t; 

and add functions these

void init_state(thread_state_t* state) {     state->active = 1;     pthread_mutex_init(&state->mutex, null); }  void remove_state(thread_state_t* state) {    state->active = 0;    pthread_mutex_destroy(&state->mutex); }  int get_active(thread_state_t* state) {     int active = 0;     pthread_mutex_lock(&state->mutex);     active = state->active;     pthread_mutex_unlock(&state->mutex);     return active; }  void set_active(thread_state_t* state, int active) {     pthread_mutex_lock(&state->mutex);     state->active = active;     pthread_mutex_unlock(&state->mutex); } 

then change loop condition state->active > 0 get_active(state) > 0 , code in main thread (sleep call here example only)

int main() {     pthread_t tid;     thread_state_t state;     init_state(&state);      pthread_create(&tid, null, t1, (void*)&state);      sleep(1);     set_active(&state, 0);      pthread_join(tid, null);     remove_state(&state);      return 0; } 

also way use pthread_cancel. not best solution.