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Module Pfs_condition


module Pfs_condition: sig .. end
Condition variables


A variant of Netmcore_condition (of Ocamlnet): It is possible to wait asynchronously for a condition. In order to do so, each waiter creates a named pipe. If the variable is signalled, a byte is written to the pipe, which wakes the waiter up.

From Netmcore_condition:

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.)

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_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 -> string -> wait_set
Creates a wait_set in the heap designated by the mutator.

The string argument is a prefix for the named pipe (e.g. "/tmp/myconditions-").

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 pipe_file : wait_entry -> string
The name of the named pipe
val wait_e : wait_entry ->
condition ->
Netmcore_mutex.mutex -> Unixqueue.event_system -> unit Uq_engines.engine
wait_e we c m esys 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 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 (or thread within the process) this problem does not occur.

Another important restriction: There must be at most one active wait_e per process or thread.

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 destroy_condition : condition -> unit
val destroy_wait_set : wait_set -> unit
Destroys these objects

Serializer


type ser 
Shared part of the serializer
val serializer_heap : Netmcore.res_id -> ser Netmcore_ref.sref
serializer_heap pool: initializes a shared structure for use with serializer. The structure needs/must only to be initialized in one of the processes using the serializer.
val serializer : ser Netmcore_ref.sref ->
Unixqueue.event_system -> string -> 'a Uq_engines.serializer_t
serializer heap esys: Creates a serializer that works across processes. The returned object exists in all processes using the serializer.

Serializer over sets of int


class type ['a] int64_serializer_t = object .. end
type int64_ser 
Shared part of the serializer
val int64_serializer_heap : Netmcore.res_id -> int -> int64_ser Netmcore_ref.sref
int_serializer_heap pool n: initializes a shared structure for use with int_serializer. The structure needs/must only to be initialized in one of the processes using the serializer. The value n is the expected value of the number of blocking callers, n >= 1. Higher values of n consume more memory and reduce the likeliness that two callers have to synchronize with each other.
val int64_serializer : int64_ser Netmcore_ref.sref ->
Unixqueue.event_system -> string -> 'a int64_serializer_t
int_serializer heap esys: Creates a serializer that works across processes. The returned object exists in all processes using the serializer.
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