The ReleaseSemaphore function increases a semaphore's count by a specified amount. External events such as kernel-mode APCs can change the wait order.Įach time one of the wait functions returns because the state of a semaphore was set to signaled, the count of the semaphore is decreased by one. Do not assume a first-in, first-out (FIFO) order. If more than one thread is waiting on a semaphore, a waiting thread is selected. For additional information about names for mutex, event, semaphore, and timer objects, see Interprocess Synchronization. ![]() Threads in other processes can open a handle to an existing semaphore object by specifying its name in a call to the OpenSemaphore function. The creating thread can also specify a name for the semaphore object. The initial count must be neither less than zero nor greater than the maximum value. The creating thread specifies the initial count and the maximum value of the count for the object. When the count is zero-indicating that the window limit has been reached-the wait function blocks execution of the window-creation code.Ī thread uses the CreateSemaphore or CreateSemaphoreEx function to create a semaphore object. The application specifies the semaphore object in call to one of the wait functions before each window is created. 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. For example, an application might place a limit on the number of windows that it creates. It acts as a gate that limits the number of threads sharing the resource to a specified maximum number. The semaphore object is useful in controlling a shared resource that can support a limited number of users. The state of a semaphore is set to signaled when its count is greater than zero, and nonsignaled when its count is zero. ![]() When the count reaches zero, no more threads can successfully wait for the semaphore object state to become signaled. The count is decremented each time a thread completes a wait for the semaphore object and incremented each time a thread releases the semaphore. Fifth would be the the ReturnLength, for example if you could recieve the name of the sempahore with this function, this parameter could hold the need buffer size after the first call with an incorrect SemaphoreInformationLength.A semaphore object is a synchronization object that maintains a count between zero and a specified maximum value. ![]() Fourth paramwter is the sizeof the struct. Thee third parameter is an pointer to an struct, wich revieces the informations. NtQuerySemaphore is easy too, first parameter is the handle to the semaphore, second the information class you want to retrive (in our case SemaphoreBasicInformation = 0x0). ![]() You dont need to use LoadLibrary, because every process has ntdll.dll loaded. Then getting the address of NtQuerySemaphore in the ntdll.dll. Okay lets get to the code, its pretty straight forward, first defining some structs you can get from. If NtQuerySemaphore fails (Status != STATUS_SUCCESS) you might want to look up the error code here. For example (nearly) all native api function, these exported by ntdll and not documented well by microsoft, return NTSTATUS, and dont use a functions simliar to get Set/GetLastError (). The code is easy, when you understand the syntax of the native api. I ommited a few thing because these would make the code even longer. Here the solution using Native Api, documented by.
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