WINAPI - QueryServiceLockStatus

Introduction

某些third-party api會在runtime去新增service，以減少使用者在安裝上的負擔。然而在系統重新啟動時，SCM會lock service database，如果新增service將會造成block。此源自: link

A service cannot call StartService during initialization. The reason is that the SCM locks the'
service control database during initialization, so a call to StartService will block. After the 
service reports to the SCM that it has successfully started, it can call StartService.

因此，我們可以先檢查SCM database是否lock，再決定我們接下來該怎麼做。

How to?

要解決這問題，可以使用:

• API: QueryServiceLockStatus。
• Command line: sc querylock。

首先來看看QueryServiceLockStatus:

BOOL IsSCMRelease(){
	SC_HANDLE hSCManager;
	LPQUERY_SERVICE_LOCK_STATUS hStatus;
	DWORD dwBytesNeeded;
	BOOL ret;
 
	hSCManager=OpenSCManager(NULL, NULL, SC_MANAGER_QUERY_LOCK_STATUS);
 
	if (hSCManager) {
		hStatus = (LPQUERY_SERVICE_LOCK_STATUS) LocalAlloc(LPTR, sizeof(QUERY_SERVICE_LOCK_STATUS)+256);
		if( hStatus == NULL ) {
			clog << "LocalAlloc failed. Error: " << GetLastError() << endl;
			return FALSE;
		}
 
		if( !QueryServiceLockStatus( hSCManager, hStatus, sizeof(QUERY_SERVICE_LOCK_STATUS)+256, &dwBytesNeeded)){
			clog << "Can't query lock status. Error: " << GetLastError() << endl;
			ret = FALSE;
		} else {
			ret = hStatus->fIsLocked == 0;
		}
 
		CloseServiceHandle(hSCManager);
		LocalFree(hStatus);
		return ret;
	}
 
	clog << "Can't open SCManager." << endl;
 
	return FALSE;
}

若透過command line:

C:\Users\tonylin>chcp 437 & sc querylock
Active code page: 437
[SC] QueryServiceLockStatus SUCCESS
        IsLocked      : FALSE
        LockOwner     :
        LockDuration  : 0 (seconds since acquired)

Reference

• MSDN - QueryServiceLockStatus
• MSDN - StartService
• MSDN - SCM Handles
• sample code
• QUERY_SERVICE_LOCK_STATUS structure