使用 C 中的线程实现 pipe

Question

I am trying implement a pipe with functions read,write,close. My main creates 2 threads, one reads from an array and writes to pipe and the other read from pipe and writes to stdout. I am using a simple circular buffer as a pipe and I used Peterson's algorithm to synchronize the two of them.

My main should wait either for them to finish their operation or receive a "quit" input from stdin in which case it should call pipe_close() and terminate the 2 threads by causing them to return

How am I supposed to get input from stdin without blocking? How can I make the threads terminate? Should I use something like Lamports algorithm to synchronize all 3 of them?

Note: I can't use any functions from pthread.h except create

void *myread(void *par) {
  //read char from array store in c
  write_to_pipe(c)
}

void *mywrite(void *par) {
  read_from_pipe(&c);
  //print to stdout
}

main() {
  //create threads
  //wait until theads return or "quit" is written in stdin, call pipe_close and cause threads to return
}

Answer 1

Assuming you do not want to get into signals, and non-block IO, consider forking another thread that will wait for STDIN, and will notify the main three to exit.

Answer 2

This questions sounds like a school assignment. If it is, you should ask a teacher for help.

You can't get input from stdin without blocking the thread that is reading from stdin . What I would do is set up two pointers for your circular buffer. One for the stdin thread and one for the stdout thread. After stdin has written data to the buffer it should update it's pointer to point to its last written element. stdout should be waiting until it sees that it's pointer is less than stdin 's pointer, and when this is the case it should write the elements of the buffer to stdout and update its own buffer after every write.

This is basically Lamport's algorithm but for two threads, one producer and one consumer.

When one thread is reading or writing to/from the buffer you might need to block the other thread from reading/writing in order to eliminate race conditions in your code.

Hope this helps.