The ObtainSemaphore() function can be used to get an exclusive lock on a semaphore. If another task currently has an exclusive or shared lock(s) on the semaphore, your task will be put to sleep until all locks on the the semaphore are released. Semaphore Nesting. ------------------ SignalSemaphores have nesting. That is, if your task already owns the semaphore, it will get a second ownership of that semaphore. This simplifies the writing of routines that must own the semaphore but do not know if the caller has obtained it yet. To obtain a semaphore use: struct SignalSemaphore *semaphore; ObtainSemaphore(semaphore); To get an exclusive lock on a public semaphore, the following code should be used: UBYTE *name; struct SignalSemaphore *semaphore; Forbid(); /* Make sure the semaphore will not go away if found. */ if (semaphore=FindSemaphore(name)) ObtainSemaphore(semaphore); Permit(); The value of semaphore is NULL if the semaphore does not exist. This is only needed if the semaphore has a chance of going away at any time (i.e., the semaphore is public and might be removed by some other program). If there is a guarantee that the semaphore will not disappear, the semaphore address could be cached, and all that would be needed is a call to the ObtainSemaphore() function.
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