Which Way of Communication is More Efficient

Question

There are two processes running in the server (LINUX), they are PHPApp and C++App. The PHPApp is written by PHP and C++App is written by C++.

Now they need to communicate with each other to perform below task: PHPApp sends a request to C++App, when the C++App receives the request it reads data from shared memory and does some calculation, finally return the data to PHPApp.

There are two methods to do above:

1. PHPApp communicates with C++App by sockets. C++App will serve as daemon process.
2. PHPApp communicates with C++App by calling exec(...) (php has such function). No C++App process until there is request from PHPApp, and in this way each request requires one C++App instance.

I wonder which way is more efficient?

UPDATE
The PHPApp is part of a server software based on Apache, thus there might be hundreds of PHPApp processes sending requests to C++App. The PHPApp makes request in parallel.

Answer 1

This depends completely on what you are trying to do. If C++App is working like a function, thus input -> C++App -> output and is not called very often then it makes sense to just call exec and spawn it.

On the other hand, if C++App has to serve a lot of requests per minute, and also in parallel, then it makes more sense to build it as a daemon that can asynchronously handle all requests. (boost::asio can help you here)

Why? Because a) communication via sockets it less expensive than spawning a new process everytime and b) because lets say you have 10 000 simultaneous requests, then the exec approach would spawn 10000 times C++App. You can imagine that this could eventually suck up all your memory. In the daemon approach, you would just have 10 000 socket connections, which boost::asio can handle without any problems.

But be careful, the async approach definitely needs good engineering. You need to write it in a way so that no requests blocks another requests and this can turn out to be quite difficult. So I would also consider this.