Communicate data between C and Python apps running continuously

问题

Is there a way to pass data between continuously running C program and continuously running Python program? It is crucial that C program starts first.

So far I have (for C side):

void run_cmd(char *cmd[])
{
    int parentID = getpid();
    char str[1*sizeof(double)];
    sprintf(str, "%d", parentID);
    char* name_with_extension;
    name_with_extension = malloc(2+strlen(cmd[1])+1*sizeof(int)+1);
    strcat(name_with_extension, cmd[1]);
    strcat(name_with_extension, " ");
    strcat(name_with_extension, str);

    pid_t pid;
    char *argv[] = {"sh", "-c", name_with_extension, NULL};
    int status;
    //printf("Run command: %s\n", cmd);
    status = posix_spawn(&pid, "/bin/sh", NULL, NULL, argv, environ);
    if (status == 0) {
        //printf("Child pid: %i\n", pid);
        //printf("My process ID : %d\n", getpid());

        //if (waitpid(pid, &status, 0) != -1) {
        //    printf("Child exited with status %i\n", status);
        //} else {
        //    perror("waitpid");
        //}

        //part below is not tested and will probably not work
        int myout[2];
        pipe(myout);
        int status;
        int ch;
        do {
            if (read(myout[0], &ch, 1)>0){
                write(1, &ch, 1);
            }
            waitpid(pid, &status, WNOHANG);
        } while (!WIFEXITED(status) && !WIFSIGNALED(status));

    }
}

For Python, I can only get the arguments list for now using:

print 'Arguments ', str(sys.argv)

As I understand from documentation, subprocess.Popen is not a way to go, since it creates a new process, which I do not want.

Embedding C in Python (or inverse) is not an option as code is too big.

I thought using process IDs and possibly sockets communicating data between, but not sure and need some advice.

The aim is to accomplish this in Windows, but unified single implementation would be better.

回答1:

You have a couple of options

Pass data through stdin and output to stdout.

You'll have to devise a line-based format, read a line from stdin and print what you want to communicate to parent process.

See the example below

Use an IPC mechanism for process communication

In this I'd propose using zmq. It's cross-platform and has quite a few features.

So, a bit of code in python showing the general idea with stdin/stdout communication

P1 (the child)

import sys                             
import time                            
i=0                                    
while True:                            
    line = sys.stdin.readline().strip()
    if not line:                       
        time.sleep(0.5)                

    if line=="ping":                   
        sys.stdout.write("pong\n")     
        sys.stdout.flush()             
        i+= 1                          

    if i > 10:                         
        sys.stdout.write("exit\n")     
        sys.stdout.flush()

P2 (the master)

import subprocess                                                                             

p = subprocess.Popen(['python', './p1.py'],stdout=subprocess.PIPE, stdin=subprocess.PIPE)     
while True:                                                                                   
    p.stdin.write("ping\n")                                                                   
    p.stdin.flush()                                                                           
    ret = p.stdout.readline().strip()                                                         
    print ret                                                                                 
    if ret=='exit':                                                                           
        exit(0)

P2 starts P1, they do 10 ping-pongs and p1 notifies p2 that it must kill itself. The processes can be long running.

来源：https://stackoverflow.com/questions/30241937/communicate-data-between-c-and-python-apps-running-continuously

标签

python

interprocess

inter-process-communicat