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CurrentScheduler Class

  • Cikk

Represents an abstraction for the current scheduler associated with the calling context.

Syntax

class CurrentScheduler;

Members

Public Methods

Name Description
Create Creates a new scheduler whose behavior is described by the _Policy parameter and attaches it to the calling context. The newly created scheduler will become the current scheduler for the calling context.
CreateScheduleGroup Overloaded. Creates a new schedule group within the scheduler associated with the calling context. The version that takes the parameter _Placement causes tasks within the newly created schedule group to be biased towards executing at the location specified by that parameter.
Detach Detaches the current scheduler from the calling context and restores the previously attached scheduler as the current scheduler, if one exists. After this method returns, the calling context is then managed by the scheduler that was previously attached to the context using either the CurrentScheduler::Create or Scheduler::Attach method.
Get Returns a pointer to the scheduler associated with the calling context, also referred to as the current scheduler.
GetNumberOfVirtualProcessors Returns the current number of virtual processors for the scheduler associated with the calling context.
GetPolicy Returns a copy of the policy that the current scheduler was created with.
Id Returns a unique identifier for the current scheduler.
IsAvailableLocation Determines whether a given location is available on the current scheduler.
RegisterShutdownEvent Causes the Windows event handle passed in the _ShutdownEvent parameter to be signaled when the scheduler associated with the current context shuts down and destroys itself. At the time the event is signaled, all work that had been scheduled to the scheduler is complete. Multiple shutdown events can be registered through this method.
ScheduleTask Overloaded. Schedules a light-weight task within the scheduler associated with the calling context. The light-weight task will be placed in a schedule group determined by the runtime. The version that takes the parameter _Placement causes the task to be biased towards executing at the specified location.

Remarks

If there is no scheduler (see Scheduler) associated with the calling context, many methods within the CurrentScheduler class will result in attachment of the process' default scheduler. This may also imply that the process' default scheduler is created during such a call.

Inheritance Hierarchy

CurrentScheduler

Requirements

Header: concrt.h

Namespace: concurrency

Create

Creates a new scheduler whose behavior is described by the _Policy parameter and attaches it to the calling context. The newly created scheduler will become the current scheduler for the calling context.

static void __cdecl Create(const SchedulerPolicy& _Policy);

Parameters

_Policy
The scheduler policy that describes the behavior of the newly created scheduler.

Remarks

The attachment of the scheduler to the calling context implicitly places a reference count on the scheduler.

After a scheduler is created with the Create method, you must call the CurrentScheduler::Detach method at some point in the future in order to allow the scheduler to shut down.

If this method is called from a context that is already attached to a different scheduler, the existing scheduler is remembered as the previous scheduler, and the newly created scheduler becomes the current scheduler. When you call the CurrentScheduler::Detach method at a later point, the previous scheduler is restored as the current scheduler.

This method can throw a variety of exceptions, including scheduler_resource_allocation_error and invalid_scheduler_policy_value.

CreateScheduleGroup

Creates a new schedule group within the scheduler associated with the calling context. The version that takes the parameter _Placement causes tasks within the newly created schedule group to be biased towards executing at the location specified by that parameter.

static ScheduleGroup* __cdecl CreateScheduleGroup();

static ScheduleGroup* __cdecl CreateScheduleGroup(location& _Placement);

Parameters

_Placement
A reference to a location where the tasks within the schedule group will be biased towards executing at.

Return Value

A pointer to the newly created schedule group. This ScheduleGroup object has an initial reference count placed on it.

Remarks

This method will result in the process' default scheduler being created and/or attached to the calling context if there is no scheduler currently associated with the calling context.

You must invoke the Release method on a schedule group when you are done scheduling work to it. The scheduler will destroy the schedule group when all work queued to it has completed.

Note that if you explicitly created this scheduler, you must release all references to schedule groups within it, before you release your reference on the scheduler, by detaching the current context from it.

Detach

Detaches the current scheduler from the calling context and restores the previously attached scheduler as the current scheduler, if one exists. After this method returns, the calling context is then managed by the scheduler that was previously attached to the context using either the CurrentScheduler::Create or Scheduler::Attach method.

static void __cdecl Detach();

Remarks

The Detach method implicitly removes a reference count from the scheduler.

If there is no scheduler attached to the calling context, calling this method will result in a scheduler_not_attached exception being thrown.

Calling this method from a context that is internal to and managed by a scheduler, or a context that was attached using a method other than the Scheduler::Attach or CurrentScheduler::Create methods, will result in an improper_scheduler_detach exception being thrown.

Get

Returns a pointer to the scheduler associated with the calling context, also referred to as the current scheduler.

static Scheduler* __cdecl Get();

Return Value

A pointer to the scheduler associated with the calling context (the current scheduler).

Remarks

This method will result in the process' default scheduler being created and/or attached to the calling context if there is no scheduler currently associated with the calling context. No additional reference is placed on the Scheduler object returned by this method.

GetNumberOfVirtualProcessors

Returns the current number of virtual processors for the scheduler associated with the calling context.

static unsigned int __cdecl GetNumberOfVirtualProcessors();

Return Value

If a scheduler is associated with the calling context, the current number of virtual processors for that scheduler; otherwise, the value -1.

Remarks

This method will not result in scheduler attachment if the calling context is not already associated with a scheduler.

The return value from this method is an instantaneous sampling of the number of virtual processors for the scheduler associated with the calling context. This value can be stale the moment it is returned.

GetPolicy

Returns a copy of the policy that the current scheduler was created with.

static SchedulerPolicy __cdecl GetPolicy();

Return Value

A copy of the policy that the current scheduler was created with.

Remarks

This method will result in the process' default scheduler being created and/or attached to the calling context if there is no scheduler currently associated with the calling context.

Id

Returns a unique identifier for the current scheduler.

static unsigned int __cdecl Id();

Return Value

If a scheduler is associated with the calling context, a unique identifier for that scheduler; otherwise, the value -1.

Remarks

This method will not result in scheduler attachment if the calling context is not already associated with a scheduler.

IsAvailableLocation

Determines whether a given location is available on the current scheduler.

static bool __cdecl IsAvailableLocation(const location& _Placement);

Parameters

_Placement
A reference to the location to query the current scheduler about.

Return Value

An indication of whether or not the location specified by the _Placement argument is available on the current scheduler.

Remarks

This method will not result in scheduler attachment if the calling context is not already associated with a scheduler.

Note that the return value is an instantaneous sampling of whether the given location is available. In the presence of multiple schedulers, dynamic resource management can add or take away resources from schedulers at any point. Should this happen, the given location can change availability.

RegisterShutdownEvent

Causes the Windows event handle passed in the _ShutdownEvent parameter to be signaled when the scheduler associated with the current context shuts down and destroys itself. At the time the event is signaled, all work that had been scheduled to the scheduler is complete. Multiple shutdown events can be registered through this method.

static void __cdecl RegisterShutdownEvent(HANDLE _ShutdownEvent);

Parameters

_ShutdownEvent
A handle to a Windows event object which will be signaled by the runtime when the scheduler associated with the current context shuts down and destroys itself.

Remarks

If there is no scheduler attached to the calling context, calling this method will result in a scheduler_not_attached exception being thrown.

ScheduleTask

Schedules a light-weight task within the scheduler associated with the calling context. The light-weight task will be placed in a schedule group determined by the runtime. The version that takes the parameter _Placement causes the task to be biased towards executing at the specified location.

static void __cdecl ScheduleTask(
    TaskProc _Proc,
    _Inout_opt_ void* _Data);

static void __cdecl ScheduleTask(
    TaskProc _Proc,
    _Inout_opt_ void* _Data,
    location& _Placement);

Parameters

_Proc
A pointer to the function to execute to perform the body of the light-weight task.

_Data
A void pointer to the data that will be passed as a parameter to the body of the task.

_Placement
A reference to a location where the light-weight task will be biased towards executing at.

Remarks

This method will result in the process' default scheduler being created and/or attached to the calling context if there is no scheduler currently associated with the calling context.

See also

concurrency Namespace
Scheduler Class
PolicyElementKey
Task Scheduler