dreamplayer-zhang / shadesmar

Fast C++ IPC using shared memory (with msgpack)

Shadesmar

Soulcast hoid pointers.

An IPC library that uses the system's shared memory to pass messages. The communication paradigm is either publish-subscibe or RPC similar to ROS and ROS2.

Required packages: Msgpack

Caution: Pre-alpha software.

Features

• Multiple subscribers and publishers.

• Multithreaded RPC support.

• Uses a circular buffer to pass messages between processes.

• Faster than using the network stack like in the case with ROS.

• Decentralized, without resource starvation.

• Allows for both serialized message passing (using msgpack) and to pass raw bytes.

• No need to define external IDL files for messages. Use C++ classes as message definition.

---

Publish-Subscribe

Publisher:

#include <shadesmar/memory/copier.h>
#include <shadesmar/pubsub/publisher.h>

int main() {
    shm::memory::DefaultCopier cpy;
    shm::pubsub::Publisher pub("topic_name", &cpy);
    const uint32_t data_size = 1024;
    void *data = malloc(data_size);
    
    for (int i = 0; i < 1000; ++i) {
        p.publish(msg, data_size);
    }
}

Subscriber:

#include <shadesmar/memory/copier.h>
#include <shadesmar/pubsub/subscriber.h>

void callback(shm::memory::Memblock *msg) {
  // `msg->ptr` to access `data`
  // `msg->size` to access `size`

  // The memory will be free'd at the end of this callback.
  // Copy to another memory location if you want to persist the data.
  // Alternatively, if you want to avoid the copy, you can call
  // `msg->no_delete()` which prevents the memory from being deleted
  // at the end of the callback.
}

int main() {
    shm::memory::DefaultCopier cpy;
    shm::pubsub::Subscriber sub("topic_name", &cpy, callback);

    // Using `spinOnce` with a manual loop
    while(true) {
        sub.spin_once();
    }
    // OR
    // Using `spin`
    sub.spin();
}

---

Publish-Subscribe (serialized messages)

For plug-and-play convenience Shadesmar supports msgpack serialization.

Message Definition (custom_message.h):

#include <shadesmar/message.h>

class InnerMessage : public shm::BaseMsg {
  public:
    int inner_val{};
    std::string inner_str{};
    SHM_PACK(inner_val, inner_str);

    InnerMessage() = default;
};

class CustomMessage : public shm::BaseMsg {
  public:
    int val{};
    std::vector<int> arr;
    InnerMessage im;
    SHM_PACK(val, arr, im);

    explicit CustomMessage(int n) {
      val = n;
      for (int i = 0; i < 1000; ++i) {
        arr.push_back(val);
      }
    }

    // MUST BE INCLUDED
    CustomMessage() = default;
};

Publisher:

#include <shadesmar/pubsub/serialized_publisher.h>
#include <custom_message.h>

int main() {
    shm::pubsub::SerializedPublisher<CustomMessage> pub("topic_name");

    CustomMessage msg;
    msg.val = 0;

    for (int i = 0; i < 1000; ++i) {
        p.publish(msg);
        msg.val++;
    }
}

Subscriber:

#include <iostream>
#include <shadesmar/pubsub/serialized_subscriber.h>
#include <custom_message.h>

void callback(const std::shared_ptr<CustomMessage>& msg) {
    std::cout << msg->val << std::endl;
}

int main() {
    shm::pubsub::SerializedSubscriber<CustomMessage> sub("topic_name", callback);

    // Using `spinOnce` with a manual loop
    while(true) {
        sub.spin_once();
    }
    // OR
    // Using `spin`
    sub.spin();
}

---

RPC (Currently broken)

Server:

#include <shadesmar/rpc/server.h>

int add(int a, int b) {
  return a + b;
}

int main() {
  shm::rpc::Function<int(int, int)> rpc_fn("add_fn", add);

  while (true) {
    rpc_fn.serve_once();
  }

  // OR...

  rpc_fn.serve();
}

Client:

#include <shadesmar/rpc/client.h>

int main() {
  shm::rpc::FunctionCaller rpc_fn("add_fn");

  std::cout << rpc_fn(4, 5).as<int>() << std::endl;
}