Программная архитектура приложений служб Service Application Programming Architecture

В основе приложений-служб Windows лежит класс, наследуемый от класса System.ServiceProcess.ServiceBase. Windows Service applications are based on a class that inherits from the System.ServiceProcess.ServiceBase class. Вы можете переопределить методы из этого класса и определить функции для них, чтобы настроить поведение службы. You override methods from this class and define functionality for them to determine how your service behaves.

Ниже перечислены основные классы, используемые при создании службы: The main classes involved in service creation are:

System.ServiceProcess.ServiceBase — вы можете переопределить методы из класса ServiceBase при создании службы и определить код, чтобы обозначить функции службы в этом наследуемом классе. System.ServiceProcess.ServiceBase — You override methods from the ServiceBase class when creating a service and define the code to determine how your service functions in this inherited class.

Кроме того, класс с именем ServiceController можно использовать для управления самой службой. In addition, a class named ServiceController can be used to manipulate the service itself. Этот класс не используется при создании службы, но может использоваться для ее запуска и остановки, а также передачи команд и возврата последовательностей перечислений. This class is not involved in the creation of a service, but can be used to start and stop the service, pass commands to it, and return a series of enumerations.

Определение поведения службы Defining Your Service’s Behavior

В классе службы вы можете переопределить функции базового класса, которые определяют, что происходит при изменении состояния службы в диспетчере служб. In your service class, you override base class functions that determine what happens when the state of your service is changed in the Services Control Manager. Класс ServiceBase предоставляет следующие методы, которые можно переопределить, чтобы добавить пользовательское поведение. The ServiceBase class exposes the following methods, which you can override to add custom behavior.

Метод Method	Переопределение Override to
OnStart	Укажите, какие действия должны быть выполнены при запуске службы. Indicate what actions should be taken when your service starts running. В этой процедуре необходимо написать код, чтобы служба выполняла требуемые задачи. You must write code in this procedure for your service to perform useful work.
OnPause	Укажите, что должно происходить при приостановке службы. Indicate what should happen when your service is paused.
OnStop	Укажите, что должно происходить при остановке службы. Indicate what should happen when your service stops running.
OnContinue	Укажите, что должно происходить при возобновлении нормальной работы службы после приостановки. Indicate what should happen when your service resumes normal functioning after being paused.
OnShutdown	Укажите, что должно происходить непосредственно перед завершением работы системы, если служба запущена в это время. Indicate what should happen just prior to your system shutting down, if your service is running at that time.
OnCustomCommand	Укажите, что должно происходить при получении службой пользовательской команды. Indicate what should happen when your service receives a custom command. Дополнительные сведения о пользовательских командах см. на сайте MSDN. For more information on custom commands, see MSDN online.
OnPowerEvent	Укажите, как должна реагировать служба при получении события управления питанием, например низкого заряда батареи или операции приостановки. Indicate how the service should respond when a power management event is received, such as a low battery or suspended operation.

Эти методы представляют состояния, через которые служба проходит за время своего существования, а именно — переходы службы от одного состояния к другому. These methods represent states that the service moves through in its lifetime; the service transitions from one state to the next. Например, служба будет отвечать на команду OnContinue только после вызова OnStart. For example, you will never get the service to respond to an OnContinue command before OnStart has been called.

Есть несколько других свойств и методов, которые представляют интерес. There are several other properties and methods that are of interest. Сюда входит следующее. These include:

Метод Run в классе ServiceBase. The Run method on the ServiceBase class. Это главная точка входа для службы. This is the main entry point for the service. При создании службы с помощью шаблона служб Windows код вставляется в метод Main приложения для запуска этой службы. When you create a service using the Windows Service template, code is inserted in your application’s Main method to run the service. Этот код выглядит так: This code looks like this:

В этих примерах используется массив типа ServiceBase. В него можно добавить каждую службу, которую содержит приложение, а затем запустить все службы одновременно. These examples use an array of type ServiceBase, into which each service your application contains can be added, and then all of the services can be run together. Если создается только одна служба, вы можете не использовать массив, а просто объявить и запустить новый объект, наследуемый от ServiceBase. If you are only creating a single service, however, you might choose not to use the array and simply declare a new object inheriting from ServiceBase and then run it. Пример см. в статье Практическое руководство. Создание служб программным способом. For an example, see How to: Write Services Programmatically.

Наборы свойств в классе ServiceBase. A series of properties on the ServiceBase class. Они определяют, какие методы могут вызываться в службе. These determine what methods can be called on your service. Например, если свойству CanStop задать значение true , в службе можно вызвать метод OnStop. For example, when the CanStop property is set to true , the OnStop method on your service can be called. Если свойству CanPauseAndContinue задать значение true , в службе можно вызвать методы OnPause и OnContinue. When the CanPauseAndContinue property is set to true , the OnPause and OnContinue methods can be called. Если одному из этих свойств задать значение true , необходимо переопределить и реализовать обработку для соответствующих методов. When you set one of these properties to true , you should then override and define processing for the associated methods.

Используемая служба должна переопределять хотя бы OnStart и OnStop. Your service must override at least OnStart and OnStop to be useful.

Можно также использовать компонент, называемый ServiceController, для обмена данными с существующей службой и управления ее поведением. You can also use a component called the ServiceController to communicate with and control the behavior of an existing service.

Introduction to Windows Service Applications

Microsoft Windows services, formerly known as NT services, enable you to create long-running executable applications that run in their own Windows sessions. These services can be automatically started when the computer boots, can be paused and restarted, and do not show any user interface. These features make services ideal for use on a server or whenever you need long-running functionality that does not interfere with other users who are working on the same computer. You can also run services in the security context of a specific user account that is different from the logged-on user or the default computer account. For more information about services and Windows sessions, see the Windows SDK documentation.

You can easily create services by creating an application that is installed as a service. For example, suppose you want to monitor performance counter data and react to threshold values. You could write a Windows Service application that listens to the performance counter data, deploy the application, and begin collecting and analyzing data.

You create your service as a Microsoft Visual Studio project, defining code within it that controls what commands can be sent to the service and what actions should be taken when those commands are received. Commands that can be sent to a service include starting, pausing, resuming, and stopping the service; you can also execute custom commands.

After you create and build the application, you can install it by running the command-line utility InstallUtil.exe and passing the path to the service’s executable file. You can then use the Services Control Manager to start, stop, pause, resume, and configure your service. You can also accomplish many of these same tasks in the Services node in Server Explorer or by using the ServiceController class.

Service Applications vs. Other Visual Studio Applications

Service applications function differently from many other project types in several ways:

The compiled executable file that a service application project creates must be installed on the server before the project can function in a meaningful way. You cannot debug or run a service application by pressing F5 or F11; you cannot immediately run a service or step into its code. Instead, you must install and start your service, and then attach a debugger to the service’s process. For more information, see How to: Debug Windows Service Applications.

Unlike some types of projects, you must create installation components for service applications. The installation components install and register the service on the server and create an entry for your service with the Windows Services Control Manager. For more information, see How to: Add Installers to Your Service Application.

The Main method for your service application must issue the Run command for the services your project contains. The Run method loads the services into the Services Control Manager on the appropriate server. If you use the Windows Services project template, this method is written for you automatically. Note that loading a service is not the same thing as starting the service. See «Service Lifetime» below for more information.

Windows Service applications run in a different window station than the interactive station of the logged-on user. A window station is a secure object that contains a Clipboard, a set of global atoms, and a group of desktop objects. Because the station of the Windows service is not an interactive station, dialog boxes raised from within a Windows service application will not be seen and may cause your program to stop responding. Similarly, error messages should be logged in the Windows event log rather than raised in the user interface.

The Windows service classes supported by the .NET Framework do not support interaction with interactive stations, that is, the logged-on user. The .NET Framework also does not include classes that represent stations and desktops. If your Windows service must interact with other stations, you will need to access the unmanaged Windows API. For more information, see the Windows SDK documentation.

The interaction of the Windows service with the user or other stations must be carefully designed to include scenarios such as there being no logged on user, or the user having an unexpected set of desktop objects. In some cases, it may be more appropriate to write a Windows application that runs under the control of the user.

Windows service applications run in their own security context and are started before the user logs into the Windows computer on which they are installed. You should plan carefully what user account to run the service within; a service running under the system account has more permissions and privileges than a user account.

Service Lifetime

A service goes through several internal states in its lifetime. First, the service is installed onto the system on which it will run. This process executes the installers for the service project and loads the service into the Services Control Manager for that computer. The Services Control Manager is the central utility provided by Windows to administer services.

After the service has been loaded, it must be started. Starting the service allows it to begin functioning. You can start a service from the Services Control Manager, from Server Explorer, or from code by calling the Start method. The Start method passes processing to the application’s OnStart method and processes any code you have defined there.

A running service can exist in this state indefinitely until it is either stopped or paused or until the computer shuts down. A service can exist in one of three basic states: Running, Paused, or Stopped. The service can also report the state of a pending command: ContinuePending, PausePending, StartPending, or StopPending. These statuses indicate that a command has been issued, such as a command to pause a running service, but has not been carried out yet. You can query the Status to determine what state a service is in, or use the WaitForStatus to carry out an action when any of these states occurs.

You can pause, stop, or resume a service from the Services Control Manager, from Server Explorer, or by calling methods in code. Each of these actions can call an associated procedure in the service (OnStop, OnPause, or OnContinue), in which you can define additional processing to be performed when the service changes state.

Types of Services

There are two types of services you can create in Visual Studio using the .NET Framework. Services that are the only service in a process are assigned the type Win32OwnProcess. Services that share a process with another service are assigned the type Win32ShareProcess. You can retrieve the service type by querying the ServiceType property.

You might occasionally see other service types if you query existing services that were not created in Visual Studio. For more information on these, see the ServiceType.

Services and the ServiceController Component

The ServiceController component is used to connect to an installed service and manipulate its state; using a ServiceController component, you can start and stop a service, pause and continue its functioning, and send custom commands to a service. However, you do not need to use a ServiceController component when you create a service application. In fact, in most cases your ServiceController component should exist in a separate application from the Windows service application that defines your service.

For more information, see ServiceController.

Requirements

Services must be created in a Windows Service application project or another .NET Framework–enabled project that creates an .exe file when built and inherits from the ServiceBase class.

Projects containing Windows services must have installation components for the project and its services. This can be easily accomplished from the Properties window. For more information, see How to: Add Installers to Your Service Application.