This module purely exists to also support "kind of anonymous" sempahores on MacOS X (which only has named semaphores). On other OS, it is just a wrapper for the functions in [root:Netsys_posix].
Note that on OS X named semaphores have a max name length of
31 characters (including the / at the beginning), and that
Netsys_sem uses 9 characters for its own purposes, leaving
22 characters for the prefix. (On other OS this is less restricted.)
true if anonymous semaphores are supported on this
system, either natively or emulated via named semaphores.
The maximum value of a semaphore, but at most
The size of an anonymous semaphore in bytes (
The container of the semaphore is the shared memory object
A name starting with a slash. Must not contain further slashes
container prefix: The prefix shall identify the container uniquely.
Once can e.g. use the path of the shared memory object. The prefix
is used to construct names for persistent objects.
Note that containers have kernel persistence! They are not
automatically deleted when the process finishes. Call
to delete containers, or
create_container to force their
creation as fresh objects.
If the container does not exist yet, it is created. Otherwise the container is just opened.
Drop the semaphores in this container, and delete the container.
This function is a no-op if the OS supports anonymous semaphores directly (because in this case the deletion of the container will automatically destroy the semaphores).
Note that there is a general problem when a container is deleted or dropped by a process while it is still being used by another one. This will generally not generate errors, but can cause a lot of confusion, because the processes will partly access the same semaphores, and partly different semaphores.
sem_init cont mem pos pshared init_value: Initializes the memory
pos + sem_size() - 1 as anonymous semaphore.
pshared the semaphore is shared between processes.
init_value is the initial non-negative value (max is
Returns the value of the semaphore. If the value is bigger than
what can be represented as
EINVAL error is returned.
The returned value is non-negative - if the underlying POSIX function reports a negative value zero is returned instead.
Unavailable on MacOS.
Locks the semaphore (decreases the value by 1). If the semaphore
value is already zero, and
SEM_WAIT_BLOCK is given, the function
waits until another process or thread posts. If
EAGAIN is returned.
sem_wait may be interrupted by signals.