Behavioral Windows Programming Interview Questions & Answers:

1. What is a thread?

A thread describes a path of execution within a process. Every time a process is initialized, the system creates a primary thread. This thread begins executing with the C/C++ run-time library's startup code, which in turn calls your entry-point function ( main , Wmain , WinMain , or WWinMain ) and continues executing until the entry-point function returns and the C/C++ run-time library's startup code calls ExitProcess

2. What is Mutex Object and why it is used?

A mutex object is a synchronization object whose state is set to signaled when it is not owned by any thread, and non-signaled when it is owned. For example, to prevent two threads from writing to shared memory at the same time, each thread waits for ownership of a mutex object before executing the code that accesses the memory. After writing to the shared memory, the thread releases the mutex object.

3. How the handles are handled in the child process?

The operating system creates the new child process but does not allow the child process to begin executing its code right away. Of course, the system creates a new, empty process handle table for the child process just as it would for any new process. But because you passed TRUE to CreateProcess's bInheritHandles parameter, the system does one more thing: it walks the parent process's handle table, and for each entry it finds that contains a valid inheritable handle, the system copies the entry exactly into the child process's handle table. The entry is copied to the exact same position in the child process's handle table as in the parent's handle table.

4. What about the usage count in the parent child process tables?

The system increments the usage count of the kernel object because two processes are now using the object. For the kernel object to be destroyed, both the parent process and the child process must either call CloseHandle on the object or terminate.

5. What do you mean by unnamed object?

When you are creating the kernel objects with the help of API's like CreateMutex(, , , ,pzname). And the Pzname parameter is NULL , you are indicating to the system that you want to create an unnamed (anonymous) kernel object. When you create an unnamed object, you can share the object across processes by using either inheritance or DuplicateHandle

6. What is the limit on per process for creating a thread?

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

7. What is Event Object and why it is used?

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

8. APIs for creating event and set and reset the events?

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

9. How do I create a Mutex?

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

10. How do other threads own the mutex?

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.