我們使用VC編寫了一個Windows服務程序後，有時候需要調整其啟動順序，比如希望在其它一些程序之前啟動自己的服務程序，則我們首先必須瞭解Windows服務的啟動機制是什麼？
Windows服務的啟動是按組來啟動的，這些組的啟動順序在註冊表中如下位置定義：
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\ServiceGroupOrder下的一個名List的REG_MULTI_SZ鍵值中可以看到。
而我們在編寫Windows服務程序時其實是可以對啟動順序進行設置的，我們先來看看CeateService函數原型：
SC_HANDLE CreateService(
SC_HANDLE hSCManager,
LPCTSTR lpServiceName,
LPCTSTR lpDisplayName,
DWORD dwDesiredAccess,
DWORD dwServiceType,
DWORD dwStartType,
DWORD dwErrorControl,
LPCTSTR lpBinaryPathName,
LPCTSTR lpLoadOrderGroup,
LPDWORD lpdwTagId,
LPCTSTR lpDependencies,
LPCTSTR lpServiceStartName,
LPCTSTR lpPassword
);
其參數描述如下：
hSCManager
[in] Handle to the service control manager database. This handle is returned by the OpenSCManager function and must have the SC_MANAGER_CREATE_SERVICE access right. For more information, see Service Security and Access Rights.
lpServiceName
[in] Pointer to a null-terminated string that specifies the name of the service to install. The maximum string length is 256 characters. The service control manager database preserves the case of the characters, but service name comparisons are always case insensitive. Forward-slash (/) and back-slash (\) are invalid service name characters.
lpDisplayName
[in] Pointer to a null-terminated string that contains the display name to be used by user interface programs to identify the service. This string has a maximum length of 256 characters. The name is case-preserved in the service control manager. Display name comparisons are always case-insensitive.
dwDesiredAccess
[in] Access to the service. Before granting the requested access, the system checks the access token of the calling process. For a list of values, see Service Security and Access Rights.
dwServiceType
[in] Service types. This parameter can be one of the following values.
SERVICE_FILE_SYSTEM_DRIVER(0x00000002) - File system driver service.
SERVICE_KERNEL_DRIVER(0x00000001) - Driver service.
SERVICE_WIN32_OWN_PROCESS(0x00000010) - Service that runs in its own process.
SERVICE_WIN32_SHARE_PROCESS(0x00000020) - Service that shares a process with one or more other services. For more information, see Service Programs.
If you specify either SERVICE_WIN32_OWN_PROCESS or SERVICE_WIN32_SHARE_PROCESS, and the service is running in the context of the LocalSystem account, you can also specify the following value.
SERVICE_INTERACTIVE_PROCESS(0x00000100) - The service can interact with the desktop. For more information, see Interactive Services.
dwStartType
[in] Service start options. This parameter can be one of the following values.
SERVICE_AUTO_START(0x00000002) - A service started automatically by the service control manager during system startup.
SERVICE_BOOT_START(0x00000000) - A device driver started by the system loader. This value is valid only for driver services.
SERVICE_DEMAND_START(0x00000003) - A service started by the service control manager when a process calls the StartService function.
SERVICE_DISABLED(0x00000004) - A service that cannot be started. Attempts to start the service result in the error code ERROR_SERVICE_DISABLED.
SERVICE_SYSTEM_START(0x00000001) - A device driver started by the IoInitSystem function. This value is valid only for driver services.
dwErrorControl
[in] Severity of the error, and action taken, if this service fails to start. This parameter can be one of the following values.
SERVICE_ERROR_CRITICAL(0x00000003) - The startup program logs the error, if possible. If the last-known-good configuration is being started, the startup operation fails. Otherwise, the system is restarted with the last-known good configuration.
SERVICE_ERROR_IGNORE(0x00000000) - The startup program logs the error but continues the startup operation.
SERVICE_ERROR_NORMAL(0x00000001) - The startup program logs the error and puts up a message box pop-up but continues the startup operation.
SERVICE_ERROR_SEVERE(0x00000002) - The startup program logs the error. If the last-known-good configuration is being started, the startup operation continues. Otherwise, the system is restarted with the last-known-good configuration.
lpBinaryPathName
[in] Pointer to a null-terminated string that contains the fully qualified path to the service binary file. If the path contains a space, it must be quoted so that it is correctly interpreted. For example, "d:\\my share\\myservice.exe" should be specified as "\"d:\\my share\\myservice.exe\"".
The path can also include arguments for an auto-start service. For example, "d:\\myshare\\myservice.exe arg1 arg2". These arguments are passed to the service entry point (typically the main function).
lpLoadOrderGroup
[in] Pointer to a null-terminated string that names the load ordering group of which this service is a member. Specify NULL or an empty string if the service does not belong to a group.
The startup program uses load ordering groups to load groups of services in a specified order with respect to the other groups. The list of load ordering groups is contained in the following registry value:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\ServiceGroupOrder
lpdwTagId
[out] Pointer to a variable that receives a tag value that is unique in the group specified in the lpLoadOrderGroup parameter. Specify NULL if you are not changing the existing tag.
You can use a tag for ordering service startup within a load ordering group by specifying a tag order vector in the following registry value:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\GroupOrderList
Tags are only evaluated for driver services that have SERVICE_BOOT_START or SERVICE_SYSTEM_START start types.
lpDependencies
[in] Pointer to a double null-terminated array of null-separated names of services or load ordering groups that the system must start before this service. Specify NULL or an empty string if the service has no dependencies. Dependency on a group means that this service can run if at least one member of the group is running after an attempt to start all members of the group.
You must prefix group names with SC_GROUP_IDENTIFIER so that they can be distinguished from a service name, because services and service groups share the same name space.
lpServiceStartName
[in] Pointer to a null-terminated string that specifies the name of the account under which the service should run. If the service type is SERVICE_WIN32_OWN_PROCESS, use an account name in the form DomainName\UserName. The service process will be logged on as this user. If the account belongs to the built-in domain, you can specify .\UserName.
If this parameter is NULL, CreateService uses the LocalSystem account. If the service type specifies SERVICE_INTERACTIVE_PROCESS, the service must run in the LocalSystem account.
If this parameter is NT AUTHORITY\LocalService, CreateService uses the LocalService account. If the parameter is NT AUTHORITY\NetworkService, CreateService uses the NetworkService account.
Windows NT: If the service type is SERVICE_WIN32_SHARE_PROCESS, you must specify the LocalSystem account. On later versions of Windows, a shared process can run as any user.
If the service type is SERVICE_KERNEL_DRIVER or SERVICE_FILE_SYSTEM_DRIVER, the name is the driver object name that the system uses to load the device driver. Specify NULL if the driver is to use a default object name created by the I/O system.
lpPassword
[in] Pointer to a null-terminated string that contains the password to the account name specified by the lpServiceStartName parameter. Specify an empty string if the account has no password or if the service runs in the LocalService, NetworkService, or LocalSystem account. For more information, see Service Record List.
Passwords are ignored for driver services.
返回值
If the function succeeds, the return value is a handle to the service.
If the function fails, the return value is NULL. To get extended error information, call GetLastError.
The following error codes can be set by the service control manager. Other error codes can be set by the registry functions that are called by the service control manager.
ERROR_ACCESS_DENIED - The handle to the SCM database does not have the SC_MANAGER_CREATE_SERVICE access right.
ERROR_CIRCULAR_DEPENDENCY - A circular service dependency was specified.
ERROR_DUPLICATE_SERVICE_NAME - The display name already exists in the service control manager database either as a service name or as another display name.
ERROR_INVALID_HANDLE - The handle to the specified service control manager database is invalid.
ERROR_INVALID_NAME - The specified service name is invalid.
ERROR_INVALID_PARAMETER - A parameter that was specified is invalid.
ERROR_INVALID_SERVICE_ACCOUNT - The user account name specified in the lpServiceStartName parameter does not exist.
ERROR_SERVICE_EXISTS - The specified service already exists in this database.
說明
The CreateService function creates a service object and installs it in the service control manager database by creating a key with the same name as the service under the following registry key:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services
Information specified by CreateService, ChangeServiceConfig, and ChangeServiceConfig2 is saved as values under this key. The following are examples of values stored for a service.
DependOnGroup - Load-ordering groups on which this service depends, as specified by lpDependencies.
DependOnService - Services on which this service depends, as specified by lpDependencies.
Description - Description specified by ChangeServiceConfig2 .
DisplayName - Display name specified by lpDisplayName.
ErrorControl - Error control specified by dwErrorControl.
FailureActions - Failure actions specified by ChangeServiceConfig2 .
Group - Load ordering group specified by lpLoadOrderGroup. Note that setting this value can override the setting of the DependOnService value.
ImagePath - Name of binary file, as specified by lpBinaryPathName.
ObjectName - Account name specified by lpServiceStartName.
Start - When to start service, as specified by dwStartType.
Tag - Tag identifier specified by lpdwTagId.
Type - Service type specified by dwServiceType.
Setup programs and the service itself can create additional subkeys for service-specific information.
The returned handle is only valid for the process that called CreateService. It can be closed by calling the CloseServiceHandle function.
If you are creating services that share a process, avoid calling functions with process-wide effects, such as ExitProcess. In addition, do not unload your service DLL.
從上面函數原型描述可以看到其有一個參數lpLoadOrderGroup和lpdwTagId，這兩個參數和服務啟動順序十分關係重大。服務啟動順序是首先根據組來決定，處於同一個組中的服務，通過Tag鍵值來排啟動順序，最後根據此服務的依賴服務來決定其啟動順序。因此我們在使用CreateService函數創建服務時，需要將lpLoadOrderGroup設置成靠前的組類別一般就可以了。
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