IoCreateNotificationEvent function (wdm.h)

Article
04/18/2022

The IoCreateNotificationEvent routine creates or opens a named notification event used to notify one or more threads of execution that an event has occurred.

Syntax

PKEVENT IoCreateNotificationEvent(
  [in]  PUNICODE_STRING EventName,
  [out] PHANDLE         EventHandle
);

Parameters

[in] EventName

Pointer to a buffer containing a null-terminated Unicode string that names the event.

[out] EventHandle

Pointer to a location in which to return a kernel handle for the event object.

Return value

IoCreateNotificationEvent returns a pointer to the created or opened event object or NULL if the event object could not be created or opened.

Remarks

If the event object does not already exist, IoCreateNotificationEvent creates and opens it, and sets its state to Signaled.

If the event object already exists, IoCreateNotificationEvent just opens the event object.

Both notification events and synchronization events are used to coordinate execution. However, while a synchronization event resets itself, a notification event remains in the Signaled state until the driver calls KeClearEvent or KeResetEvent.

To synchronize on a notification event:

Open the notification event with IoCreateNotificationEvent. Identify the event with the EventName string.
Wait for the event to be signaled by calling KeWaitForSingleObject with the PKEVENT returned by IoCreateNotificationEvent. More than one thread of execution can wait for a given notification event. To poll instead of stall, specify a Timeout of zero to KeWaitForSingleObject.
Close the handle to the notification event with ZwClose when access to the event is no longer needed.

There are two main methods for sharing event objects:

The user-mode application creates the event object and passes a handle to the object to the driver by sending an IOCTL to the driver. The driver must handle the IOCTL in the context of the process that created the event object and must validate the handle by calling ObReferenceObjectByHandle. This method is the recommended method for sharing event objects between user and kernel modes.
The driver creates a named event object in the global \BaseNamedObjects object directory. To access a kernel-mode event from user-mode, use the name Global\\Xxx. Note that security settings can prevent an application from opening the event. The \\BaseNamedObjects object directory is not created until the Microsoft Win32 subsystem initializes, so drivers that are loaded at boot time cannot create event objects in the \\BaseNamedObjects directory in their DriverEntry routines.

For more information about events, see Event Objects.

Requirements

Requirement	Value
Minimum supported client	Available starting with Windows 2000.
Target Platform	Universal
Header	wdm.h (include Wdm.h, Ntddk.h, Ntifs.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe
IRQL	PASSIVE_LEVEL
DDI compliance rules	HwStorPortProhibitedDDIs(storport), IrqlIoPassive4(wdm)