How to Gracefully Interrupt a Blocking ServerSocket.accept() Method?

Interrupting a Blocking ServerSocket Accept() Method

In a multi-threaded application, it may be necessary to interrupt a blocking method such as ServerSocket.accept(). This is typically required for graceful shutdown or to respond to administrative commands.

The traditional accept() method blocks until a client connection is received. This behavior can hinder the ability to respond to external events or terminate the application promptly.

Solution: Using Close() to Interrupt

One effective solution to interrupt the blocking accept() method is to call close() on the ServerSocket object from a separate thread. When close() is invoked, the accept() method will throw a SocketException.

<code class="java">// In the admin thread
ServerSocket serverSocket = ...;
serverSocket.close();</code>

Handling the Interruption

Within the main loop where accept() is being called, it is necessary to catch the SocketException and handle it gracefully.

<code class="java">while (listening) {
    try {
        // Accept client connection
        Socket clientSocket = serverSocket.accept();
        // ... Process client connection
    } catch (SocketException e) {
        // Handle the interruption
        // ... Shut down client threads, admin thread, and main thread
        break;
    }
}</code>

Benefits of This Approach

• Allows for graceful shutdown of the application, even while accept() is blocking.
• Provides a reliable way to interrupt the blocking method without having to modify the ServerSocket class itself.

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