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IPC Keys

System V IPC keys are integer values represented using the data type key_t. The IPC get calls translate a key into the corresponding integer IPC identifier. These calls guarantee that if we create a new IPC object, then that object will have a unique identifier, and that if we specify the key of an existing object, then we’ll always obtain the (same) identifier for that object. (Internally, the kernel maintains data structures mapping keys to identifiers for each IPC mechanism, as described in Section 45.5.)

So, how do we provide a unique key—one that guarantees that we won’t accidentally obtain the identifier of an existing IPC object used by some other application? There are three possibilities:


  

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