Object Manager (Windows)

Object Manager is the centralized resource broker in the Windows NT line of operating systems, which keeps track of the resources allocated to processes. It is resource-agnostic and can manage any type of resource, including device and file handles. All resources are represented as objects, each belonging to a logical namespace for categorization and having a type that represents the type of the resource, which exposes the capabilities and functionalities via properties. An object is kept available until all processes are done with it; Object Manager maintains the record of which objects are currently in use via reference counting, as well as the ownership information. Any system call that changes the state of resource allocation to processes goes via the Object Manager.

Objects can either be Kernel objects or Executive objects. Kernel objects represent primitive resources such as physical devices, or services such as synchronization, which are required to implement any other type of OS service. Kernel objects are not exposed to user mode code, but are restricted to kernel code. Applications and services running outside the kernel use Executive objects, which are exposed by the Windows Executive, along with its components such as the memory manager, scheduler and I/O subsystem. Executive objects encapsulate one or more kernel objects and expose not only the kernel and kernel-mediated resources, but also an expanded set of services that the kernel does. Applications themselves can wrap one or more Executive objects and surface objects that offer certain services. Executive objects are also used by the environment subsystems (such as the Win32 subsystem, the OS/2 subsystem, the POSIX subsystem, etc.) to implement the functionality of the respective environments.

Whenever an object is created or opened, a reference to the instance, called a handle, is created. Object Manager indexes the objects both by their names as well as the handles. But, referencing the objects by the handles is faster because the name translation can be skipped. Handles are associated with processes (by making an entry into the process' Handle table that lists the handles it owns) and can be transferred between processes as well. A process must own a handle to an object before using it. A process can own a maximum of 16,000,000 handles at one time. During creation, a process gains handles to a default set of objects. While there exists different types of handles - file handles, event handles and process handles - they only help in identifying the type of the target objects; not in distinguishing the operations that can be performed through them, thus providing consistency to how various object types are handled programmatically. Handle creation and resolution of objects from handles are solely mediated by Object Manager, so no resource usage goes unnoticed by it.

The types of Executive objects exposed by Windows NT are:

typedef struct _OBJECT_ATTRIBUTES {
  ULONG Length;
  HANDLE RootDirectory;
  PUNICODE_STRING ObjectName;
  ULONG Attributes;
  PSECURITY_DESCRIPTOR SecurityDescriptor;
  PSECURITY_QUALITY_OF_SERVICE SecurityQualityOfService;
} OBJECT_ATTRIBUTES *POBJECT_ATTRIBUTES;

OBJ_INHERIT
OBJ_PERMANENT
OBJ_EXCLUSIVE
OBJ_CASE_INSENSITIVE
OBJ_OPENIF
OBJ_OPENLINK
OBJ_KERNEL_HANDLE

Object Manager paths are available to many Windows API file functions, although Win32 names like \\?\ and \\.\ for the local namespaces suffice for most uses.[1] Using the former in Win32 user-mode functions translates directly to \??, but using \?? is still different as this NT form does not turn off pathname expansion.[2]

Tools that serve as explorers in the Object Manager namespaces are available. These include the 32-bit WinObj from Sysinternals[3] and the 64-bit WinObjEx64.[4]

• Architecture of Windows NT

• Object Manager Routines (Windows Drivers)
• Channel9 Interview