Performing Inter-Process Communication

libnick uses named-pipes on Windows and Unix Domain Sockets on Linux and macOS to establish inter process server and client communicators, while abstracting all of that away from the consumer in the easy to use Nickvision::App::InterProcessCommunicator API.

Upon creating an Nickvision::App::InterProcessCommunicator object, either isServer() or isClient() will return true depending on whether or not this instance is a server or client respectively. Server instances should register a callback to the CommandReceived event to be invoked when clients send commands to the server.

NOTE: Server instance of Nickvision::App::InterProcessCommunicator should be kept alive for the entire need for the communicator. This includes when the need to receive client messages is present.

Let's consider an example scenario for using the Nickvision::App::InterProcessCommunicator. Assume we have an application where we want the first instance to be considered the main, running instance. Assume that if other instances of said application are started, we want its arguments to be passed to the main instance and then have said other instances be closed. This will allow, for example, a GUI main instance to be manipulated via secondary CLI instances.

Here's the code for this:

using namespace Nickvision::App;
using namespace Nickvision::Events;
 
int main(int argc, char*[] argv)
{
    std::vector<std::string> modernArgs;
    for(int i = 0; i < argc; i++)
    {
        if(argv[i])
        {
            modernArgs.push_back({ argv[i] });
        }
    }
    InterProcessCommunicator& ipc{ "appid" };
    ipc.commandReceived() += handleArguments;
    ipc.communicate(modernArgs, true);
}
 
void handleArguments(const ParamEventArgs<std::vector<std::string>>& args)
{
  ...
}

If this program is ran for the first time, ipc will be the server instance. The handleArguments function will be invoked after communicate with its own arguments, as communicate still invokes CommandReceived even if ipc is the server instance.

If this program is ran not for the first time, its arguments will be sent to the first instance and this instance itself will close (as true was passed as the second argument of communicate). The first instance's handleArguments function will be called as a result of CommandReceived being invoked by the ipc server receiving the command.