_lwp_park() can be used to synchronize access to resources among multiple light-weight processes. It causes the calling LWP to wait interruptably in the kernel, until one of the following conditions is met:
•
The abstime argument is non-NULL, and the absolute UTC time it specifies has passed.
•
The LWP receives a directed signal posted using _lwp_kill(), or is elected to handle a signal on behalf of its containing process.
•
The LWP is awoken by another LWP in the same process that has made a call to _lwp_wakeup().
•
The LWP is awoken by another LWP in the same process that has made a call to _lwp_unpark() or _lwp_unpark_all().
The preferred method to awaken an LWP sleeping as a result of a call to
_lwp_park() is to make a call to
_lwp_unpark(), or
_lwp_unpark_all(). The
_lwp_wakeup() system call is a more general facility, and requires more resources to execute.
The optional
hint argument specifies the address of object upon which the LWP is synchronizing. When the
hint value is matched between calls to
_lwp_park() and
_lwp_unpark() or
_lwp_unpark_all(), it may reduce the time necessary for the system to resume execution of waiting LWPs.
The
unpark and
unparkhint arguments can be used to fold a park operation and unpark operation into a single system call. If
unpark is non-zero, the system will behave as if the following call had been made before the calling thread begins to wait:
_lwp_unpark(unpark, unparkhint);