module Netmcore_condition:Condition variablessig..end
Netmcore_heap), for example in the header field of
Netmcore_array or somewhere else in heap-allocated
data structures.
In order to ensure that the condition variable is in the heap, the
special function create_condition must be used to initialize it
there. As create_condition requires a mutator as argument, this is
only possible by calling create_condition from the callback of
Netmcore_heap.modify.
Condition variables are special values, and cannot be copied or moved.
Condition variables are implemented on top of semaphores. Compared to
the pthreads version of condition variables, the user needs here to
allocate special wait_entry slots, one for each process. An entry
can be used for all condition variables a process needs to wait for.
(Actually, such entries also exist in typical pthreads implementations,
but are hidden from the user in the thread control block. We just
don't have here a place where we could allocate process-specific
shared memory.)
type
type
wait needs a wait_entry. These entries
can be used for several condition variables, so typically each process
has only one entry for each heap.type
wait_entry, for easier management. This set can e.g. be
stored side by side with the condition variable(s). It is important
that the wait_set resides in the same shared heap as the
condition variable.val dummy_condition : unit -> conditioncondition-typed variablesval dummy_wait_set : unit -> wait_setwait_set is non-functional, but can be used to put something
into wait_set-typed variablesval create_condition : Netmcore_heap.mutator -> conditioncreate m: Creates a condition variable, and
pushes it to the heap, using the mutator m.
After being pushed to the heap, the variable can be used. It is
nonsense to copy it outside the heap.
val create_wait_set : Netmcore_heap.mutator -> wait_setwait_set in the heap designated by the mutatorval alloc_wait_entry : Netmcore_heap.mutator ->
wait_set -> wait_entrywait_entryval free_wait_entry : Netmcore_heap.mutator ->
wait_set -> wait_entry -> unitwait_entryval wait : wait_entry ->
condition -> Netmcore_mutex.mutex -> unitwait we c m atomically unlocks the mutex m and suspends the
calling process on the condition variable c. The process will
restart after the condition variable c has been signalled.
The mutex m is locked again before wait returns.
At the time of calling, the wait_entry we must not be used to
manage another wait. When allocating a separate wait_entry
per process this problem does not occur.
val signal : condition -> unitsignal c restarts one of the processes waiting on the
condition variable c.val broadcast : condition -> unitbroadcast c restarts all processes waiting on the
condition variable c.val destroy_condition : condition -> unitval destroy_wait_set : wait_set -> unit