Module Netmcore_condition

module Netmcore_condition: sig .. end

Condition variables

Condition variables are here defined as values that reside in shared heaps (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.)

Since Ocamlnet-3.5, there are also special wait entries wait_entry_e which can be used to wait from within a running Unixqueue. For each such wait entry, however, a named pipe needs to be allocated.

type condition

The condition variable

type wait_entry

Each process that wants to 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_e

A special kind of wait_entry for intergration into an event loop

type wait_set

A set of 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 -> condition

A dummy condition is non-functional, but can be used to put something into condition-typed variables

val dummy_wait_set : unit -> wait_set

A dummy wait_set is non-functional, but can be used to put something into wait_set-typed variables

val create_condition : Netmcore_heap.mutator -> condition

create 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_set

Creates a wait_set in the heap designated by the mutator

val alloc_wait_entry : Netmcore_heap.mutator ->
       wait_set -> wait_entry

Allocates a wait_entry

val free_wait_entry : Netmcore_heap.mutator ->
       wait_set -> wait_entry -> unit

Frees a wait_entry

val alloc_wait_entry_e : Netmcore_heap.mutator ->
       wait_set -> string -> wait_entry_e

alloc_wait_entry_e mut set filename: Allocates a new wait entry with notification via named pipe. The filename must refer to an existing named pipe.

val free_wait_entry_e : Netmcore_heap.mutator ->
       wait_set -> wait_entry_e -> unit

Frees a wait_entry_e. The named pipe is deleted.

val wait : wait_entry ->
       condition -> Netmcore_mutex.mutex -> unit

wait 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 wait_e : ?debug_name:string ->
       wait_entry_e ->
       condition ->
       Netmcore_mutex.mutex ->
       Unixqueue.event_system ->
       (unit -> 'a Uq_engines.engine) -> 'a Uq_engines.engine

Like wait, but the suspension is done by waiting on a named pipe event (i.e. "nonblocking suspension"):

wait_e we c m esys cont atomically unlocks the mutex m and suspends the calling engine on the condition variable c. The engine will restart after the condition variable c has been signalled. The mutex m is locked again, at which time cont is called. The result of cont() is the result of wait_e.

At the time of calling, the wait_entry_e we must not be used to manage another wait_e. When allocating a separate wait_entry_e per process (or thread within the process) this problem does not occur.

val signal : condition -> unit

signal c restarts one of the processes waiting on the condition variable c.

val broadcast : condition -> unit

broadcast c restarts all processes waiting on the condition variable c.

val pipe_name : wait_entry_e -> string

Returns the name of the pipe

val destroy_condition : condition -> unit

val destroy_wait_set : wait_set -> unit

Destroys these objects

module Debug: sig .. end

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