作業 (電腦)

(重定向自工作 (資訊科學)

在計算機科學中,作業(英語:job)和工作(英語:task,又譯為任務)是在記憶體中的一組程式指令。它包括了一段虛擬定址空間分頁,與作業系統資源,提供執行緒運行的空間。有時候,它與行程被認為是同義的;但也有人認為,在即時系統(real-time)中運行的行程才被稱為作業。

Windows作业对象

Windows 2000操作系统开始,job是一组进程的集合,用于限制其使用的资源、性能信息统计维护、自动关闭子进程等。允许将进程组合在一起并创建一个进程的"容器"来限制进程能够做什么。无法将当前进程或它的任何子进程从作业中去除,这个安全特性可以确保进程无法摆脱对它施加的限制。Win32关于作业的API:

  • CreateJobObject:创建作业内核对象。若该作业已经存在,则返回一个指向该作业的句柄
  • OpenJobObject:打开命名的作业内核对象
  • CloseHandle:关闭一个作业内核对象句柄(不会自动终止作业中的进程)
  • IsProcessInJob:验证某一个进程是否存在于作业中
  • AssignProcessToJobObject:增加一个进程句柄到一个作业内核对象
  • TerminateJobObject:终止一个作业的所有进程
  • SetInformationJobObject:给job设置资源限制。作业句柄参数不能传递NULL值,以防止进程删除施加于自己身上的限制
  • QueryJobInformationObject:查询job资源限制。进程可以调用它获得其所属作业的相关信息(作业句柄参数传递NULL值),使进程能看到自己被施加了哪些限制。

使用CreateProcess创建的子进程默认属于父进程所在的job,除非CreateProcess函数的dwCreationFlags参数设置了CREATE_BREAKAWAY_FROM_JOB标志。这种情况下,不能用AssignProcessToJobObject函数把子进程关联入job。

作业的所有进程都终止,则作业对象被触发(signaled)。

示例

#include <windows.h>
int main()
{
	HANDLE hJob = CreateJobObject(0, 0);
	if (hJob)
	{
		//JOBOBJECT_EXTENDED_LIMIT_INFORMATION jeli;
		//memset(&jeli, 0, sizeof(jeli));
		//jeli.BasicLimitInformation.LimitFlags = JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;

                //Place some restrictions on processes in the job.
                JOBOBJECT_BASIC_LIMIT_INFORMATION jobli = { 0 }; 
                jobli.PriorityClass = IDLE_PRIORITY_CLASS;//The process always runs in the idle priority class.
                jobli.PerJobUserTimeLimit.QuadPart = 10000000;  //The job cannot use more than 1 second of CPU time. 100-ns pricision
                jobli.LimitFlags = JOB_OBJECT_LIMIT_PRIORITY_CLASS | JOB_OBJECT_LIMIT_JOB_TIME;
      
		if (SetInformationJobObject(hJob, JobObjectExtendedLimitInformation, &jobli, sizeof(jobli)))
		{
			if (AssignProcessToJobObject(hJob, GetCurrentProcess()))
			{
				WinExec("notepad.exe", SW_SHOW); 
//I assume that there will never be more than 10 processes in this job.
#define MAX_PROCESS_IDS     10
				//Calculate the number of bytes needed for  structure  & process IDs.
				DWORD Cb = sizeof(JOBOBJECT_BASIC_PROCESS_ID_LIST) +
					(MAX_PROCESS_IDS - 1) * sizeof(DWORD);

				//Allocate the block of memory.
				PJOBOBJECT_BASIC_PROCESS_ID_LIST pjobpil = PJOBOBJECT_BASIC_PROCESS_ID_LIST)_alloca(Cb);

				//Tell the function the maximum number of processes  that we allocated space for.
				pjobpil->NumberOfAssignedProcesses = MAX_PROCESS_IDS;

				//Request the current set of process IDs.
				BOOL bRes = QueryInformationJobObject(hJob, JobObjectBasicProcessIdList,
					pjobpil, Cb, &Cb);

				//Enumerate the process IDs.
				for (int x = 0; x < pjobpil->NumberOfProcessIdsInList; x++)
				{
					wchar_t ExeName[1024];
					DWORD len = 1024;

					HANDLE hProcess = OpenProcess(PROCESS_ALL_ACCESS, TRUE, pjobpil->ProcessIdList[x]);
					
					BOOL Res = QueryFullProcessImageName(
						hProcess, //_In_    HANDLE hProcess,
						NULL, //_In_    DWORD  dwFlags,
						ExeName, //_Out_   LPTSTR lpExeName,
						&len //_Inout_ PDWORD lpdwSize
					);
					DWORD dwLastError =GetLastError();
				}	 
			}		
		}
                CloseHandle(hJob);
	}
	return 0;
}

參見