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<concept xml:lang="en" id="GUID-9D00655C-AFBA-5DF7-B11B-6B2355BDF08D"><title>Using Semaphores</title><prolog><metadata><keywords/></metadata></prolog><conbody><p>Semaphores are provided to synchronise co-operating threads. They are Kernel objects and, as such, are managed by the Kernel.</p> <p>Access to a semaphore is through an RSemaphore handle.</p> <p>The semaphores are counting semaphores, having a <codeph>TInt</codeph> count value that is incremented by calling the <codeph>Signal()</codeph> member function of the semaphore handle and decremented by calling the <codeph>Wait()</codeph> member function of the semaphore handle. A semaphore with a negative value implies that a thread must wait for the completion of some event.</p> <p>The mechanism by which a thread waits on a semaphore is part of the overall management of thread scheduling.</p> <p>For general applications, it is not common to explicitly create a semaphore; most applications are interested in making asynchronous requests to service providers. When a thread is created, a <keyword>request
        semaphore</keyword> is also created that support asynchronous requests.</p> <p>After making one or more asynchronous requests, a thread calls User::WaitForAnyRequest() to wait for one of the requests to complete or calls User::WaitForRequest() to wait for a specific request to complete. A service provider calls User::RequestComplete() to signal request completion.</p> </conbody></concept>