While another socket reaches out to the other to form a connection.

The server forms the listener socket while the client reaches out to the server.

TCP is a communication protocol that was introduced in 1974.

Transport Layer uses the port numbers to create a process to process communications.

Before any data transfer activity, TCP established a connection.

One entity who is waiting for connection is server and another entity is a client connects to the server.

The receiver always sends acknowledgements (ACKs) for segments.

It seems to work, but when I run my app in Apple Instruments I can see this app uses about 100 CPU and the main reason 95 of it accounts for call to non-blocking accept().

I think I have added this non-blocking accept() method call in order to be able to stop server in any time by clicking GUI button Stop Server.

Shut down the server by connecting to it over localhost and sending it a shutdown command in whatever protocol you are using.

No flag needed, no non-blocking loop required, no selectpollepoll required, no CPU waste, no memory-bandwidth waste.

After someone connects it check whether it is real mobile phone client or my shutdown client.

I think this is interesting approach and I will give it try Please give write this in answer I accept it as good solution to my problem.

Provide details and share your research But avoid Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

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C Socket Accept Return 0