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GenServer - The Generic Server Behaviour
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== GenServer - The Generic Server Behaviour == [[File:GenServer_logo.png|right|thumbnail|150px]] '''GenServer''' is a crucial behaviour in the [[Elixir]] programming language for building concurrent and fault-tolerant applications. It provides a convenient framework for creating and managing server processes. == Overview == GenServer is a part of the [[OTP]] ([[Open Telecom Platform]]) framework present in the Elixir standard library. It allows developers to create server processes and define their behavior based on a set of callbacks. These callbacks enable processing of incoming messages, maintaining state, and handling events such as timeouts or termination. == Key Features == GenServer offers several features that make it a powerful tool for building robust applications: === Simplified Server Process Creation === GenServer simplifies the creation of server processes by providing a set of functions such as `start_link` and `start`. These functions handle the process creation and initialization, abstracting away the complexities of low-level process management. === Asynchronous Message Passing === The GenServer behaviour enables asynchronous message passing between processes through the use of the `cast` and `async_*` functions. This allows for non-blocking communication and helps in building highly concurrent systems. === Synchronous Message Handling === GenServer also supports synchronous message handling, where a caller can send a message to a server process and wait for a response using the `call` function. This facilitates building request-response interactions between processes. === State Management === The state of a GenServer process can be stored and manipulated using the `handle_*` callback functions. These functions provide mechanisms to initialize, update, and query the server process's state. State management is essential for maintaining the server's behavior and application-specific data. === Error Handling === GenServer helps in building fault-tolerant systems by offering error handling mechanisms such as trapping exits, linking processes, and handling multiple types of error scenarios. With these features, developers can build applications that recover gracefully from failures. === Behavioral Callbacks === The GenServer behaviour defines a set of predefined callbacks that developers can implement to define the behavior of server processes. These callbacks include `init/1`, `handle_call/3`, `handle_cast/2`, `handle_info/2`, and `terminate/2`, among others. By implementing these callbacks, developers can customize the behavior of their server processes. == Usage Examples == [[File:Code_example.png|left|thumbnail|250px]] Below are a couple of examples demonstrating the usage of GenServer: === Example 1: Counter === This example demonstrates a simple counter server implemented using GenServer. ```elixir defmodule CounterServer do use GenServer def start_link(init_value) do GenServer.start_link(__MODULE__, init_value) end def init(init_value) do {:ok, init_value} end def handle_cast(:increment, state) do {:noreply, state + 1} end end ``` === Example 2: Key-Value Store === This example showcases a basic key-value store built with GenServer. ```elixir defmodule KeyValueStore do use GenServer def start_link() do GenServer.start_link(__MODULE__, %{}) end def init(state) do {:ok, state} end def handle_call({:get, key}, _from, state) do {:reply, Map.get(state, key), state} end def handle_call({:put, key, value}, _from, state) do {:reply, :ok, Map.put(state, key, value)} end end ``` == Further Reading == * [[OTP]]: Provides more information on the OTP framework within Elixir. * [[Process]]: Explains processes and their lifecycle in Elixir. * [[Concurrency]]: Discusses various aspects of concurrency in Elixir. == See Also == * [[Supervisor]]: Details the Supervisor behavior for building fault-tolerant systems. * [[Application]]: Guides developers on managing Elixir applications effectively. == References == {{Reflist}} [[Category:Elixir Programming Language]] [[Category:Concurrency]] [[Category:OTP]]
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