Intel Extensible Firmware Interface - Manual (Page 109)

Services — Boot Services
Version 1.10 12/01/02 5-11
WaitForEvent()
Summary
Stops execution until an event is signaled.
Prototype
EFI_STATUS
WaitForEvent (
IN UINTN NumberOfEvents,
IN EFI_EVENT *Event,
OUT UINTN *Index
);
Parameters
NumberOfEvents The number of events in the Event array.
Event An array of EFI_EVENT . Type EFI_EVENT is defined in the
CreateEvent() function description.
Index Pointer to the index of the event which satisfied the wait condition.
Description
The WaitForEvent() function waits for any event in the Event array to be signaled. On
success, the signaled state of the event is cleared and execution is returned with Index indicating
which event caused the return. It is possible for an event to be signaled before being waited on. In
this case, the next wait operation for that event would immediately return with the signaled event.
Waiting on an event of type EVT_NOTIFY_SIGNAL is not permitted. If any event in Event is of
type EVT_NOTIFY_SIGNAL , WaitForEvent() returns EFI_INVALID_PARAMETER and
sets Index to indicate which event caused the failure. This function must be called at priority
level TPL_APPLICATION . If an attempt is made to call it at any other priority level,
EFI_UNSUPPORTED is returned.
To wait for a specified time, a timer event must be included in the Event array.
WaitForEvent() will always check for signaled events in order, with the first event in the array
being checked first. To check if an event is signaled without waiting, an already signaled event can
be used as the last event in the list being checked, or the
CheckEvent() interface may be used.
Status Codes Returned
EFI_SUCCESS The event indicated by Index was signaled.
EFI_INVALID_PARAMETER The event indicated by Index has a notification function or
Event was not a valid type.
EFI_UNSUPPORTED The current TPL is not TPL_APPLICATION .