[ACCEPTED]-How can Unix pipes be used between main process and thread?-unix

Accepted answer
Score: 14

Yes its possible through pipes.

Step one 6 call pipe to get a pipe:

  #include <unistd.h>

  int main(...)

    int fileDescriptors[2];

Step 2 pass the fileDescriptors[0] to 5 the main process, and fileDescriptors1 to 4 the thread. In Main you wait for the pipe 3 to be written to to by reading from fileDescriptors[0]

    char msg[100];
    read(fileDescriptors[0], msg, 100);  // block until pipe is read

Step 2 3, from your thread write to fileDescritpors1 1 when the signal occurs

 void signal_handler( int sig )
     // Write to the file descriptor
     if (sig == SIGKILL)
         const char* msg = "Hello Mama!";
         write(fileDescriptors[1], msg, strlen(msg));
Score: 4

It can be done, but it's rather unnecessary. Pipes 4 are intended for inter-process communication. Threads 3 share the same memory and can therefore 2 communicate directly, as long as you use 1 locking correctly.

Score: 1

If you're talking about pipe() rather than |, then 4 yes. Pipes can generally just be treated 3 as a file descriptor. You just need to 2 open the pipe and cleanup the input in one 1 thread, and the output in the other.

Score: 0

As others have said, this may be more trouble 8 than it is worth.

However, if you insist.

Probably 7 easiest just to open two pipes using popen and 6 rw mode before spawning the thread. Choose 5 one for main-->thread and the other for 4 main<--thread and just go ahead.

Or you 3 could open a total of four file descriptors 2 after spawning, as if they were two different 1 processes

Score: 0

You could do that, apache has a similar 14 "graceful restart" option. (see 13 here). You would use something like:

#include <sys/types.h>
#include <signal.h>

kill(getppid(), SIGUSR1);

To send 12 a signal to the parent. Others have the 11 code above to spawn the file descriptors 10 and catch it on the parent side.

However, I 9 tend to avoid signals for scripted interprocess 8 communication, instead using them only for 7 "user sent" messages, like start/stop/restart/refresh. What 6 you replace them with depends on your usecase: you 5 could use a messaging variable, or if your 4 main process is in a server loop, you could 3 "select" on a pipe at the top of the loop to see 2 if the child has sent a refresh message. There 1 is probably a lot of others I'm missing.

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