Object Manager: Difference between revisions

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{{Refimprove|date=March 2019}}

[[File:Object Manager (Windows) screenshot.png|thumb|Object Manager in Windows, categorized hierarchically using ''namespaces'']]

'''Object Manager''' (internally called '''Ob''') is a subsystem implemented as part of the [[Windows Executive]] which manages Windows ''resources''. Resources, which are surfaced as logical ''objects'', each reside in a namespace for categorization. Resources can be physical devices, files or folders on volumes, [[Windows Registry|Registry]] entrieskeys or even running processes. All objects representing resources have an <code>Object Type</code> property and other metadata about the resource. Object Manager is a shared resource, and all subsystems that deal with the resources have to pass through the Object Manager.

==Architecture==

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!File

| An open [[fileFile (computing)|file]], [[Directory (computing)|directory]] or an [[I/O]] device.

|NtCreateFile<br />NtOpenFile

|-

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!Access token

| The identity, properties, privileges and access rights forof a process anor objectthread.

|NtCreateToken<br />NtDuplicateToken<br />NtOpenProcessToken<br />NtOpenThreadToken

|-

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!Timer

| An objectsobject which notifies processes at fixed intervals.

|NtCreateTimer<br />NtOpenTimer

|-

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A <code>Type</code> object contains properties unique to the type of the object as well as static methods that implement the services offered by the object. Objects managed by Object Manager must at least provide a predefined set of services: <code>Close</code> (which closes a handle to an object), <code>Duplicate</code> (create another handle to the object with which another process can gain shared access to the object), <code>Query object</code> (gather information about its attributes and properties), <code>Query security</code> (get the [[security descriptor]] of the object), <code>Set security</code> (change the security access), and <code>Wait</code> (to synchronize with one or more objects via certain events). Type objects also have some common attributes, including the type name, whether they are to be allocated in non-paged memory, access rights, and synchronization information. All instances of the same type share the same type object, and the type object is instantiated only once. A new object type can be created by endowing an object with Properties to expose its state and methods to expose the services it offers.

<code>Object name</code> is used to give a descriptive identity to an object, to aid in object lookup. Object Manager maintains the list of names already assigned to objects being managed, and maps the names to the instances. Since most object accesses occur via handles, it is not always necessary to look up the name to resolve into the object reference. Lookup is only performed when an object is created (to make sure the new object has a unique name), or a process accesses an object by its name explicitly. <code>Object directories</code> are used to categorize them according to the types. Predefined directories include <code>\??</code> alias <code>\DosDevices</code> (device names), <code>\BaseNamedObjects</code> (Mutexesmutexes, events, semaphores, waitable timers, and section objects), <code>\Callback</code> (callback functions), <code>\Device</code>, <code>\Driver</code>, <code>\FileSystem</code>, <code>\KnownDlls</code>, <code>\Nls</code> (language tables), <code>\ObjectTypes</code> (type objects), <code>\RPC Control</code> ([[Remote Procedure Call|RPC]] ports), <code>\Security</code> (security subsystem objects), and <code>\Windows</code> (windowing subsystem objects). Objects also belong to a ''Namespace''. Each user session is assigned a different namespace. Objects shared between all sessions are in the ''GLOBAL'' namespace, and (logon) session-specific objects are in the specific (logon) session namespaces

OBJECT_ATTRIBUTES structure: