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Windows OS Interview Questions

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A semaphore object is a synchronization object that maintains a count between zero and a specified maximum value. The count is decremented each time a thread completes a wait for the semaphore object and incremented each time a thread releases the semaphore. When the count reaches zero, no more threads can successfully wait for the semaphore object state to become signaled. The state of a semaphore is set to signaled when its count is greater than zero, and non-signaled when its count is zero. The semaphore object is useful in controlling a shared resource that can support a limited number of users. It acts as a gate that limits the number of threads sharing the resource to a specified maximum number. For example, an application might place a limit on the number of windows that it creates. It uses a semaphore with a maximum count equal to the window limit, decrementing the count whenever a window is created and incrementing it whenever a window is closed. The application specifies the semaphore object in call to one of the wait functions before each window is created. When the count is zero - indicating that the window limit has been reached - the wait function blocks execution of the window-creation code. 

A thread uses the CreateMutex function to create a mutex object. The creating thread can request immediate ownership of the mutex object and can also specify a name for the mutex object 

CreateEvent- to create the event
OpenEvent - to open already created event
SetEvent - to set the event signaled state
RestEvent - To set the Event To non-Signaled State 

Event is the thread synchronization object to set signaled state or non-signaled state. 

The number of threads a process can create is limited by the available virtual memory and depends on the default stack size 

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