Inter-Process Communication

# Three IPC styles, modelled to expose the difference that matters:
# what each does to message boundaries, and whether it copies.
pipe_buf = []

def pipe_write(data):          # byte stream: boundaries are lost on the way in
    pipe_buf.extend(data)

pipe_write("hello")
pipe_write("world")

reads = 0
while pipe_buf:                # 10 bytes come back in chunks of 4, not as 2 writes
    del pipe_buf[:4]
    reads += 1

shm = {"value": 0}             # shared memory: mapped, so nothing is copied
shm["value"] = 42
copies = 0

queue = ["hello", "world"]     # message queue: each send stays one message

print(f"pipe: {reads} reads for 2 writes | shm: {copies} copies "
      f"| queue: {len(queue)} messages")

#include <deque>
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main() {
    // Three IPC styles, modelled to expose the difference that matters:
    // what each does to message boundaries, and whether it copies.
    deque<char> pipeBuf;
    auto pipeWrite = [&](const string& data) {   // byte stream: boundaries lost
        for (char c : data) pipeBuf.push_back(c);
    };
    pipeWrite("hello");
    pipeWrite("world");
    int reads = 0;
    while (!pipeBuf.empty()) {   // 10 bytes come back in 4s, not as 2 writes
        for (int i = 0; i < 4 && !pipeBuf.empty(); i++) pipeBuf.pop_front();
        reads++;
    }
    int shmValue = 0; // shared memory: mapped, so nothing is copied
    shmValue = 42;
    int copies = 0;
    vector<string> queue = {"hello", "world"}; // each send stays one message
    cout << "pipe: " << reads << " reads for 2 writes | shm: " << copies
    << " copies | queue: " << queue.size() << " messages\n";
}

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.List;
class Main {
    public static void main(String[] args) {
        // Three IPC styles, modelled to expose the difference that matters:
        // what each does to message boundaries, and whether it copies.
        Deque<Character> pipeBuf = new ArrayDeque<>();
        for (String data : new String[]{"hello", "world"}) // boundaries lost
        for (char c : data.toCharArray()) pipeBuf.add(c);
        int reads = 0;
        while (!pipeBuf.isEmpty()) {   // 10 bytes come back in 4s, not as 2 writes
            for (int i = 0; i < 4 && !pipeBuf.isEmpty(); i++) pipeBuf.poll();
            reads++;
        }
        int shmValue = 42; // shared memory: mapped, nothing copied
        int copies = 0;
        List<String> queue = List.of("hello", "world"); // one message each
        System.out.println("pipe: " + reads + " reads for 2 writes | shm: "
        + copies + " copies | queue: " + queue.size() + " messages");
    }
}