It must be possible to set maxsem to at least 65535. This system call allocates a control block to the created semaphore, setting the initial count to isemcnt and maximum count (upper limit) to maxsem. Error is reported if it is attempted to return resources to a semaphore that would cause this maximum count to be exceeded.Ĭreates a semaphore, assigning to it a semaphore ID. To prevent too many resources from being returned to a semaphore, a maximum resource count can be set for each semaphore. A task waiting for semaphore resources is put in the semaphore queue. If the number of semaphore resources is insufficient (i.e., further reducing the semaphore resource count would cause it to be negative), a task attempting to acquire resources goes into WAITING state until the next time resources are returned. When a task (the task waiting for an event) acquires n resources, it decreases the semaphore resource count by n. When a task (the task making event notification) returns m resources, it increments the semaphore resource count by m. The ID number for the semaphore is called a semaphore ID.Ī semaphore contains a resource count indicating whether the corresponding resource exists and in what quantity, and a queue of tasks waiting to acquire the resource. A semaphore is an object identified by an ID number. Functions are provided for creating and deleting a semaphore, acquiring and returning resources corresponding to semaphores, and referencing semaphore status. A semaphore is used to realize mutual exclusion control and synchronization when using a resource. A semaphore is an object indicating the availability of a resource and its quantity as a numerical value.
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