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== OTP GenServer == [[File:Elixir logo.png|thumb|150px|right|Elixir logo]] The OTP GenServer is a behavior module provided by the Elixir programming language that allows developers to build robust and concurrent server processes. It is a fundamental part of the OTP (Open Telecom Platform) framework, which provides a set of building blocks for building scalable and fault-tolerant applications. === Overview === The OTP GenServer is designed to simplify the implementation of server processes in Elixir. It provides a standard set of callback functions that can be implemented to define the behavior of the server. Developers can create their own modules that implement the `GenServer` behavior and then spawn instances of these modules as processes. === Key Features === The OTP GenServer offers several key features that make it a powerful tool for building reliable and concurrent applications: * **Synchronous and Asynchronous Calls**: Clients can interact with the GenServer either synchronously or asynchronously, depending on their requirements. Synchronous calls block the calling process until a response is received, while asynchronous calls do not block and allow the calling process to continue its execution. * **State Management**: The GenServer can maintain its own internal state, which can be accessed and modified through well-defined callbacks. This allows the server to store and manipulate data across multiple client interactions. * **Message Handling**: The GenServer processes messages sequentially, ensuring that only one message is processed at a time. This guarantees that the server's state remains consistent during concurrent requests. * **Error Handling**: The GenServer provides built-in error handling mechanisms that allow developers to gracefully handle errors and failures within the server process. Error handling can be customized through the implementation of error callback functions. * **Process Monitoring**: The GenServer can be monitored by other processes, allowing for supervision and fault tolerance. If a GenServer process crashes, it can be automatically restarted or terminated based on the supervision strategy specified. === Usage === To use the OTP GenServer, developers need to create a module that implements the `GenServer` behavior and define the necessary callback functions. These callback functions include: * `init/1`: Initializes the state of the GenServer process. * `handle_cast/2`: Handles asynchronous messages sent to the GenServer. * `handle_call/3`: Handles synchronous messages sent to the GenServer. * `handle_info/2`: Handles non-message system events sent to the GenServer. * `terminate/2`: Cleans up the GenServer process before it terminates. Once the module is defined, developers can start a GenServer process using the `GenServer.start/3` function. This function takes the name of the module, the initial state, and optional parameters. The GenServer process can then be interacted with by sending messages using the `GenServer.call/2` or `GenServer.cast/2` functions. === Example === Here is a simple example that demonstrates the usage of the OTP GenServer: ```elixir defmodule CounterServer do use GenServer def init(initial_count) do {:ok, initial_count} end def handle_call(:increment, _from, count) do {:reply, count + 1, count + 1} end end {:ok, pid} = GenServer.start(CounterServer, 0) GenServer.call(pid, :increment) ``` In this example, we define a `CounterServer` module that increments a counter state. When `:increment` is called synchronously on the GenServer process, it replies with the updated count. The `GenServer.start/3` function is used to start the GenServer process and obtain its process identifier, which is then used to make the synchronous call using `GenServer.call/2`. === See Also === * [[OTP]] * [[Supervisor]] * [[Application]] == References == {{reflist}}
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