This project demonstrates how to use PHP's stream functions to perform non-blocking, asynchronous operations in a client-server environment with TCP sockets. The files that comprise the client and server programs each total 42 lines in length.
First, run the server at a command shell:
$ php server.php # server
The server accepts TCP socket connections from clients. When a client connects, the server immediately checks for a new socket connection or data available to read on an existing client socket.
When the server receives a request from a client, it sleeps for a second, which could instead be other useful work. Then it responds to the client and closes the connection.
At another command shell (aka client1), prepare the following command, but don't run it yet:
$ php client.php 10 # client1
Once it has connected to the server and sent a request, client1 will sleep 10 seconds, which could instead be some
other useful work. Then it tries to read from the server socket connection once every 10 seconds. Upon receiving a
response from the server, it echoes the message that it receives. The client exits after the server has closed the
connection.
In yet another command shell (aka client2), prepare the following command, but don't run it yet:
$ php client.php 5 # client2
This client2 instance will sleep for 5 seconds, whereas client1 sleeps for 10. We will run client1 first, but
client2 should finish first, because both the clients and servers operate in a non-blocking, asynchronous fashion.
Now that the server is running and the client shells are prepared to execute, run the client in client1, and then
quickly (i.e., within 5 seconds) run the client in client2.
The server shell should have output similar to the following:
2016-11-27 12:54:07: Server listening...
2016-11-27 12:54:14: Accepting client connection
2016-11-27 12:54:14: Received from client: Hello, server!
2016-11-27 12:54:14: Working for 1 second...
2016-11-27 12:54:15: Responding
2016-11-27 12:54:15: Accepting client connection
2016-11-27 12:54:15: Received from client: Hello, server!
2016-11-27 12:54:15: Working for 1 second...
2016-11-27 12:54:16: Responding
Note the times of the various server events. The server listens for 7 seconds before client1 connects and sends a
request. The server sleeps for a second before it responds to client1, then it immediately accepts the connection and
request from client2. Again it sleeps for a second before responding to client2.
The client1 process should have generated output similar to the following:
2016-11-27 12:54:14: Connecting...
2016-11-27 12:54:14: Connected to server. Making server request...
2016-11-27 12:54:14: Requested
2016-11-27 12:54:14: Waiting for server response...
2016-11-27 12:54:24: Received server response: 2016-11-27 12:54:15: Hello, client! We received "Hello, server!" from you.
2016-11-27 12:54:24: Doing some useful work...
2016-11-27 12:54:34: Connection closed
The client1 process sleeps for 10 seconds before receiving the server response, and then it sleeps for another 10
seconds after receiving the server response and before closing the connection.
The output for client2 should be similar to the following:
2016-11-27 12:54:15: Connecting...
2016-11-27 12:54:15: Connected to server. Making server request...
2016-11-27 12:54:15: Requested
2016-11-27 12:54:15: Waiting for server response...
2016-11-27 12:54:20: Received server response: 2016-11-27 12:54:16: Hello, client! We received "Hello, server!" from you.
2016-11-27 12:54:20: Doing some useful work...
2016-11-27 12:54:25: Connection closed
Although client2 connected to the server after client1, client2 finished its work before client1.
The client and server programs each accept two arguments. The first argument is the number of seconds that it should
sleep, and the second argument is the TCP socket specification (e.g., tcp://127.0.0.1:3333, the default).
As demonstrated by this project, PHP's stream functions may be used to implement non-blocking, asynchronous processing.
The event loop implementations of Icicle and React are a couple of well-known examples. This approach also resembles the way in which the event loop in Node.js operates.