Win32 Programming

Win32 Programming Lesson 8a: Jobs

Where are we? • Grouping processes into logical groups: Jobs • However, processes don’t retain a parent-child relationship which can make life difficult… very difficult

Jobs • Introduced in Windows 2000 • Based upon the Job Kernel Object • Ability to add restrictions to processes (and groups of processes)

CreateJobObject • HANDLE CreateJobObject( PSECURITY_ATTRIBUTES psa, PCTSTR pszName); • Like most calls, we first name our Job Object… can also open an existing object: • HANDLE OpenJobObject( DWORD dwDesiredAccess, BOOL bInheritHandle, PCTSTR pszName);

Placing Restrictions on a Job • Jobs can be restricted in several ways • Resource Limits • UI Limits • Security limits (registry, subkeys, files etc.) • Set by: • BOOL SetInformationJobObject( HANDLE hJob, JOBOBJECTINFOCLASS JobObjectInformationClass, PVOID pJobObjectInformation, DWORD cbJobObjectInformationLength);

JobObjectInfoClass • Enumerated type setting the limit type • Basic Limit • Extended Basic Limit • Basic UI Restrictions • Security Limit • Defines the type of the 3rd Parameter in the call

Basic Limits • typedef struct _JOBOBJECT_BASIC_LIMIT_INFORMATION { LARGE_INTEGER PerProcessUserTimeLimit; LARGE_INTEGER PerJobUserTimeLimit; DWORD LimitFlags; DWORD MinimumWorkingSetSize; DWORD MaximumWorkingSetSize; DWORD ActiveProcessLimit; DWORD_PTR Affinity; DWORD PriorityClass; DWORD SchedulingClass; } JOBOBJECT_BASIC_LIMIT_INFORMATION, *PJOBOBJECT_BASIC_LIMIT_INFORMATION;

Extended Limits • typedef struct _JOBOBJECT_EXTENDED_LIMIT_INFORMATION { JOBOBJECT_BASIC_LIMIT_INFORMATION BasicLimitInformation; IO_COUNTERS IoInfo; SIZE_T ProcessMemoryLimit; SIZE_T JobMemoryLimit; SIZE_T PeakProcessMemoryUsed; SIZE_T PeakJobMemoryUsed; } JOBOBJECT_EXTENDED_LIMIT_INFORMATION, *PJOBOBJECT_EXTENDED_LIMIT_INFORMATION;

UI Limits • JOB_OBJECT_UILIMIT_EXITWINDOWS Prevents processes from logging off, shutting down, rebooting, or powering off the system via the ExitWindowsEx function • JOB_OBJECT_UILIMIT_READCLIPBOARDPrevents processes from reading the clipboard • JOB_OBJECT_UILIMIT_WRITECLIPBOARDPrevents processes from erasing the clipboard • JOB_OBJECT_UILIMIT_SYSTEMPARAMETERSPrevents processes from changing system parameters via the SystemParametersInfo function • JOB_OBJECT_UILIMIT_DISPLAYSETTINGSPrevents processes from changing the display settings via the ChangeDisplaySettings function • JOB_OBJECT_UILIMIT_GLOBALATOMSGives the job its own global atom table and restricts processes in the job to accessing only the job's table • JOB_OBJECT_UILIMIT_DESKTOPPrevents processes from creating or switching desktops using the CreateDesktop or SwitchDesktop function • JOB_OBJECT_UILIMIT_HANDLESPrevents processes in a job from using USER objects (such as HWNDs) created by processes outside the same job

Placing a Process in a Job • BOOL AssignProcessToJobObject( HANDLE hJob, HANDLE hProcess); • Create the job… • Place restrictions on the job… • CreateProcess with CREATE_SUSPENDED • Call AssignProcessToJob • New processes spawned by a job are automatically part of the job

Terminating All Processes in A Job • Simple! • BOOL TerminateJobObject( HANDLE hJob, UINT uExitCode);

Job Accounting • Fairly simple • Uses JOBOBJECT_BASIC_ACCOUNTING_INFORMATION • See http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/base/isprocessinjob.asp

Notifications • It is possible to receive notifications from jobs as they complete, but it’s somewhat complicated • Should be aware of the I/O Completion Port Kernel Object • Example: JobLab example application

Win32 Programming