osfmk/man/semaphore_create.html

   1 <h2>semaphore_create</h2>
<hr>
<p>
<strong>Function</strong> - Create a new semaphore.
<h3>SYNOPSIS</h3>
<pre>
<strong>kern_return_t    semaphore_create</strong>
              <strong>(task_t</strong>                   <var>task</var>,
             <strong>semaphore_t</strong>        <var>*semaphore</var>,
             <strong>int</strong>                    <var>policy</var>,
             <strong>int</strong>                     <var>value</var><strong>);</strong>
</pre>
<h3>PARAMETERS</h3>
<dl>
<dt> <var>task</var>
<dd>
[in task port] The task receiving the send right of the newly created semaphore.
<p>
<dt> <var>semaphore</var>
<dd>
[out send right] The port naming the created semaphore.
<p>
<dt> <var>policy</var>
<dd>
[in scalar] The blocked thread wakeup policy for the newly created semaphore. Valid policies are:
<dl>
<p>
  <dt> SYNC_POLICY_FIFO
<dd>
a first-in-first-out policy for scheduling thread wakeup.
     <p>
  <dt> SYNC_POLICY_FIXED_PRIORITY
<dd>
a fixed priority policy for scheduling thread wakeup.
     </dl>
     <p>
<dt> <var>value</var>
<dd>
[in scalar] The initial value of the semaphore count.
</dl>
<h3>DESCRIPTION</h3>
<p>
The <strong>semaphore_create</strong> 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
<strong>semaphore_create</strong>) and exporting (via <strong>device_get_status</strong>)
semaphores for
user level access. Device driver semaphore creation is done at device
initialization time. Device drivers may support multiple semaphores.
<h3>RETURN VALUES</h3>
<dl>
  <p>
<dt> <strong>KERN_INVALID_ARGUMENT</strong>
<dd>
The task argument or the policy argument was invalid,
     or the initial value of the semaphore was invalid.
     <p>
<dt> <strong>KERN_RESOURCE_SHORTAGE</strong>
<dd>
The kernel could not allocate the semaphore.
     <p>
<dt> <strong>KERN_SUCCESS</strong>
<dd>
The semaphore was successfully created.
</dl>
<h3>RELATED INFORMATION</h3>
<p>
Functions:
<a href="semaphore_destroy.html"><strong>semaphore_destroy</strong></a>,
<a href="semaphore_signal.html"><strong>semaphore_signal</strong></a>,
<a href="semaphore_signal_all.html"><strong>semaphore_signal_all</strong></a>,
<a href="semaphore_wait.html"><strong>semaphore_wait</strong></a>,
<a href="device_get_status.html"><strong>device_get_status</strong></a>.