module Weak: sig .. end
Arrays of weak pointers and hash tables of weak pointers.
Low-level functions
type 'a t
The type of arrays of weak pointers (weak arrays). A weak
pointer is a value that the garbage collector may erase whenever
the value is not used any more (through normal pointers) by the
program. Note that finalisation functions are run after the
weak pointers are erased.
A weak pointer is said to be full if it points to a value,
empty if the value was erased by the GC.
Notes:
- Integers are not allocated and cannot be stored in weak arrays.
- Weak arrays cannot be marshaled using
Pervasives.output_value
nor the functions of the Marshal module.
val create : int -> 'a t
Weak.create n returns a new weak array of length
n.
All the pointers are initially empty. Raise
Invalid_argument
if
n is negative or greater than
Sys.max_array_length-1.
val length : 'a t -> int
Weak.length ar returns the length (number of elements) of
ar.
val set : 'a t -> int -> 'a option -> unit
Weak.set ar n (Some el) sets the
nth cell of
ar to be a
(full) pointer to
el;
Weak.set ar n None sets the
nth
cell of
ar to empty.
Raise
Invalid_argument "Weak.set" if
n is not in the range
0 to
Weak.length a - 1.
val get : 'a t -> int -> 'a option
Weak.get ar n returns None if the
nth cell of
ar is
empty,
Some x (where
x is the value) if it is full.
Raise
Invalid_argument "Weak.get" if
n is not in the range
0 to
Weak.length a - 1.
val get_copy : 'a t -> int -> 'a option
Weak.get_copy ar n returns None if the
nth cell of
ar is
empty,
Some x (where
x is a (shallow) copy of the value) if
it is full.
In addition to pitfalls with mutable values, the interesting
difference with
get is that
get_copy does not prevent
the incremental GC from erasing the value in its current cycle
(
get may delay the erasure to the next GC cycle).
Raise
Invalid_argument "Weak.get" if
n is not in the range
0 to
Weak.length a - 1.
val check : 'a t -> int -> bool
Weak.check ar n returns
true if the
nth cell of
ar is
full,
false if it is empty. Note that even if
Weak.check ar n
returns
true, a subsequent
Weak.get ar n can return
None.
val fill : 'a t -> int -> int -> 'a option -> unit
Weak.fill ar ofs len el sets to el all pointers of ar from
ofs to ofs + len - 1. Raise Invalid_argument "Weak.fill"
if ofs and len do not designate a valid subarray of a.
val blit : 'a t -> int -> 'a t -> int -> int -> unit
Weak.blit ar1 off1 ar2 off2 len copies len weak pointers
from ar1 (starting at off1) to ar2 (starting at off2).
It works correctly even if ar1 and ar2 are the same.
Raise Invalid_argument "Weak.blit" if off1 and len do
not designate a valid subarray of ar1, or if off2 and len
do not designate a valid subarray of ar2.
Weak hash tables
A weak hash table is a hashed set of values. Each value may
magically disappear from the set when it is not used by the
rest of the program any more. This is normally used to share
data structures without inducing memory leaks.
Weak hash tables are defined on values from a
Hashtbl.HashedType
module; the
equal relation and
hash function are taken from that
module. We will say that
v is an instance of
x if
equal x v
is
true.
The
equal relation must be able to work on a shallow copy of
the values and give the same result as with the values themselves.
module type S = sig .. end
The output signature of the functor
Weak.Make.
module Make:
Functor building an implementation of the weak hash table structure.