Win32 Event Objects

Win32 Event Objects

2:54 AM

Introduction

A Win32 event is a system object that provides for inter-thread communication which supports two states - signaled and Non-signaled.
  1. Signaled State - (Active or On) Used by waiting threads to know that they may proceed.
  2. Non-signaled State - (Not Active or Off) indicates to waiting threads that they must continue to wait.
There are two types of events: manual-reset and auto-reset.
  • Manual-Reset Event
    • An explicit call to the Win32 API ResetEvent() must be made to move the event from the signaled to Non-signaled state. The syntax for the ResetEvent is given below:
 BOOL WINAPI ResetEvent(HANDLE hEvent);
    • A call to the Win32 API SetEvent() is made to move from the Non-signaled state to signaled state. 
BOOL WINAPI SetEvent(HANDLE hEvent);
  • An Auto-Reset Event
    • Moves from the signaled to Non-signaled state automatically without a call to ResetEvent().
    • However, a call to SetEvent() must still be made to move to the signaled state.

Create Event Object

Win32 API provides a function called CreateEvent, which is used to create the event thread synchronization object. The manual or auto reset event choice is passed to the function as a parameter. The syntax for the function is given below:

HANDLE WINAPI CreateEvent(
  LPSECURITY_ATTRIBUTES lpEventAttributes,
  BOOL bManualReset,
  BOOL bInitialState,
  LPCTSTR lpName
           );

Event Functions


Event function
Description
CreateEvent
Creates or opens a named or unnamed event object.
CreateEventEx
Creates or opens a named or unnamed event object and returns a handle to the object.
OpenEvent
Opens an existing named event object.
PulseEvent
Sets the specified event object to the signaled state and then resets it to the nonsignaled state after releasing the appropriate number of waiting threads.
ResetEvent
Sets the specified event object to the nonsignaled state.
SetEvent
Sets the specified event object to the signaled state.
  

Wait Functions


Wait function
Description
MsgWaitForMultipleObjects
Waits until one or all of the specified objects are in the signaled state or the time-out interval elapses. The objects can include input event objects.
MsgWaitForMultipleObjectsEx
Waits until one or all of the specified objects are in the signaled state, an I/O completion routine or asynchronous procedure call (APC) is queued to the thread, or the time-out interval elapses. The array of objects can include input event objects.
RegisterWaitForSingleObject
Directs a wait thread in the thread pool to wait on the object.
SignalObjectAndWait
Signals one object and waits on another object as a single operation.
UnregisterWait
Cancels a registered wait operation.
UnregisterWaitEx
Cancels a registered wait operation.
WaitForMultipleObjects
Waits until one or all of the specified objects are in the signaled state or the time-out interval elapses.
WaitForMultipleObjectsEx
Waits until one or all of the specified objects are in the signaled state, an I/O completion routine or asynchronous procedure call (APC) is queued to the thread, or the time-out interval elapses.
WaitForSingleObject
Waits until the specified object is in the signaled state or the time-out interval elapses.
WaitForSingleObjectEx
Waits until the specified object is in the signaled state, an I/O completion routine or asynchronous procedure call (APC) is queued to the thread, or the time-out interval elapses.
WaitOnAddress
Waits for the value at the specified address to change.
WaitOrTimerCallback
An application-defined function that serves as the starting address for a timer callback or a registered wait callback.
WakeByAddressAll
Wakes all threads waiting for the value of an address to change.
WakeByAddressSingle
Wakes a thread waiting for the value of an address to change.




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