第5章 win32 api 多线程编程.ppt

* Present introduction to Windows event objects. An Event object can be used to notify one or more threads about an occurrence of some kind. This means that these Windows objects can be used to signal other threads about events such as computations have completed or data is available or a message is ready to be received. Events are kernel objects and are represented by a HANDLE. This HANDLE is not valid until you call the CreateEvent() function. An event can be in one of the two possible states: signaled and nonsignaled. When the state of the event shifts from nonsignaled to signaled, one or more threads waiting for the event are released to continue execution. Threads can wait for a single event by using the WaitForSingleObject() function, and wait for many events or one of many events by using the WaitForMultipleObjects() function. Clarify their queries (if any) related to this slide. * Present details on the two types of Events and how they differ. The two types of Windows events are: Auto-reset Events: An auto-reset event stays signaled until one waiting thread is released. The signal state is persistent, which means that the event will remain in the signaled state until one thread that has waited on the event has been released. After the thread is released, the state of the event is reset to nonsignaled. Manual reset Events: A manual reset event stays signaled until it is explicitly reset to nonsignaled by an API call. When a manual reset event is signaled, all waiting threads are released. Since the event must be manually reset to the nonsignaled state, any thread, other than those waiting for the event when the event was signaled, could enter a wait on the event, and will be released before the event is reset. Clarify their queries (if any) related to this slide. * Present details along with parameter involved in the CreateEvent() function to create and initialize an event object. lpEventAttributes: This parameter is a pointer to a SECURITY_ATTRIBU