c - Sending signals between three threads -

i had write program uses 3 threads - 1 read letters, second count characters, , third output them. code:

#include <stdio.h> #include <stdlib.h> #include <sys/stat.h> #include <unistd.h> #include <linux/stat.h> #include <pthread.h> #include <string.h> #include <signal.h>  int first[2]; int second[2];  void *input(void *ptr) {    char str[100];    int length;     while(1)    {       printf("enter message: ");       fflush(stdout);       length = read(stdin_fileno, str, sizeof(str));        if(str[0] == ';')          exit(2);        if(length <= 0)       {          if(length == -1)             perror("read");          close(first[1]);          exit(2);       }        if(write(first[1], str, length) != length)       {          perror("write");          exit(2);       }    } }  void *countchars(void *ptr) {    char str[100];    int length, count = 0;     while(1)    {       length = read(first[0], str, sizeof(str));       if(length <= 0)       {          if(length == -1)             perror("read");          close(first[0]);          close(second[1]);          exit(2);       }       if(write(stdout_fileno, str, length) != length)       {          perror("write");          exit(2);       }        while(str[count] != '\n') count++;        write(second[1], &count, sizeof(count));        count = 0;    } }  void *output(void *ptr) {    int length, count = 0;     while(1)    {       length = read(second[0], &count, sizeof(count));       if(length < sizeof(count))       {          close(second[0]);          exit(2);       }        printf("number of characters: %d\n", count);    } }  int main() {    pthread_t t1, t2, t3;     if(pipe(first) == -1)    {       printf("first pipe error");       exit(1);    }     if(pipe(second) == -1)    {       printf("second pipe error");       exit(1);    }     pthread_create(&t1, null, input, null);    pthread_create(&t2, null, countchars, null);    pthread_create(&t3, null, output, null);     pthread_join(t1, null);    pthread_join(t2, null);    pthread_join(t3, null);     return 0; } 

it works, right have implement signals here. sending sigusr1 signal should stop program execution until sending sigusr2 signal.

the problem when send signal, 1 thread gets it. , have use fifo inform other threads signal executed , execute in rest of them.

how this?

signals delivered process, not threads. thread able handle signal may used call signal handler. need figure out how handle signal , decide how communicate threads. have not described mean "stop program execution", i'll have guess.

i suggest using combination of pthread_sigmask , sigwait. can use pthread_sigmask disable automatic handling of sigusr1 , sigusr2 in worker threads. call sigwait in fourth signal handler thread explicitly handle signals. when signal handler thread receives sigusr1 sets global flag. worker threads check flag periodically , go sleep (on condition variable maybe?) when set. signal handler thread loops around , calls sigwait again. when receives sigusr2, wakes worker threads, loops around , calls sigwait, once again.