osfmk/man/semaphore_create.html
Function - Create a new semaphore.
**kern\_return\_t semaphore\_create**** (task\_t **task,** semaphore\_t **\*semaphore,** int **policy,** int **value** );**
task[in task port] The task receiving the send right of the newly created semaphore.
semaphore[out send right] The port naming the created semaphore.
policy[in scalar] The blocked thread wakeup policy for the newly created semaphore. Valid policies are:
SYNC_POLICY_FIFOa first-in-first-out policy for scheduling thread wakeup.
SYNC_POLICY_FIXED_PRIORITYa fixed priority policy for scheduling thread wakeup.
value[in scalar] The initial value of the semaphore count.
The semaphore_create function creates a new semaphore, associates the created semaphore with the specified task, and returns a send right naming the new semaphore. In order to support a robust producer/consumer communication service, Interrupt Service Routines (ISR) must be able to signal semaphores. The semaphore synchronizer service is designed to allow user-level device drivers to perform signal operations, eliminating the need for event counters. Device drivers which utilize semaphores are responsible for creating (via semaphore_create ) and exporting (via device_get_status ) semaphores for user level access. Device driver semaphore creation is done at device initialization time. Device drivers may support multiple semaphores.
KERN_INVALID_ARGUMENT The task argument or the policy argument was invalid, or the initial value of the semaphore was invalid.
KERN_RESOURCE_SHORTAGE The kernel could not allocate the semaphore.
KERN_SUCCESS The semaphore was successfully created.
Functions: semaphore_destroy, semaphore_signal, semaphore_signal_all, semaphore_wait, device_get_status.