1Stdlib.Weak(3)                   OCaml library                  Stdlib.Weak(3)
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NAME

6       Stdlib.Weak - no description
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Module

9       Module   Stdlib.Weak
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Documentation

12       Module Weak
13        : (module Stdlib__Weak)
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23   Low-level functions
24       type 'a t
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27       The type of arrays of weak pointers (weak arrays).  A weak pointer is a
28       value that the garbage collector may erase whenever the  value  is  not
29       used  any more (through normal pointers) by the program.  Note that fi‐
30       nalisation functions are run before the weak pointers are  erased,  be‐
31       cause  the  finalisation  functions can make values alive again (before
32       4.03 the finalisation functions were run after).
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34       A weak pointer is said to be full if it points to a value, empty if the
35       value was erased by the GC.
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37       Notes:
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39       -Integers are not allocated and cannot be stored in weak arrays.
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41       -Weak  arrays  cannot be marshaled using output_value nor the functions
42       of the Marshal module.
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47       val create : int -> 'a t
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50       Weak.create n returns a new weak array of length n .  All the  pointers
51       are initially empty.
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54       Raises  Invalid_argument  if  n  is  not  comprised  between  zero  and
55       Obj.Ephemeron.max_ephe_length (limits included).
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59       val length : 'a t -> int
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62       Weak.length ar returns the length (number of elements) of ar .
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66       val set : 'a t -> int -> 'a option -> unit
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69       Weak.set ar n (Some el) sets the n th cell of ar to be a (full) pointer
70       to el ; Weak.set ar n None sets the n th cell of ar to empty.
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73       Raises  Invalid_argument if n is not in the range 0 to Weak.length ar -
74       1 .
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78       val get : 'a t -> int -> 'a option
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81       Weak.get ar n returns None if the n th cell of  ar  is  empty,  Some  x
82       (where x is the value) if it is full.
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85       Raises  Invalid_argument if n is not in the range 0 to Weak.length ar -
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90       val get_copy : 'a t -> int -> 'a option
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93       Weak.get_copy ar n returns None if the n th cell of ar is empty, Some x
94       (where  x is a (shallow) copy of the value) if it is full.  In addition
95       to pitfalls with mutable values, the interesting difference with get is
96       that  get_copy  does  not  prevent  the incremental GC from erasing the
97       value in its current cycle ( get may delay the erasure to the  next  GC
98       cycle).
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101       Raises  Invalid_argument if n is not in the range 0 to Weak.length ar -
102       1 .
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104       If the element is a custom block it is not copied.
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108       val check : 'a t -> int -> bool
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111       Weak.check ar n returns true if the n th cell of ar is full,  false  if
112       it is empty.  Note that even if Weak.check ar n returns true , a subse‐
113       quent Weak.get ar n can return None .
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116       Raises Invalid_argument if n is not in the range 0 to Weak.length ar  -
117       1 .
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121       val fill : 'a t -> int -> int -> 'a option -> unit
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124       Weak.fill ar ofs len el sets to el all pointers of ar from ofs to ofs +
125       len - 1 .
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128       Raises Invalid_argument if ofs and len do not designate a valid  subar‐
129       ray of ar .
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133       val blit : 'a t -> int -> 'a t -> int -> int -> unit
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136       Weak.blit  ar1  off1  ar2  off2  len  copies len weak pointers from ar1
137       (starting at off1 ) to ar2 (starting at off2  ).   It  works  correctly
138       even if ar1 and ar2 are the same.
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141       Raises Invalid_argument if off1 and len do not designate a valid subar‐
142       ray of ar1 , or if off2 and len do not designate a  valid  subarray  of
143       ar2 .
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148   Weak hash sets
149       A  weak  hash  set is a hashed set of values.  Each value may magically
150       disappear from the set when it is not used by the rest of  the  program
151       any  more.   This is normally used to share data structures without in‐
152       ducing memory leaks.  Weak hash sets  are  defined  on  values  from  a
153       Hashtbl.HashedType  module;  the  equal  relation and hash function are
154       taken from that module.  We will say that v is  an  instance  of  x  if
155       equal x v is true .
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157       The equal relation must be able to work on a shallow copy of the values
158       and give the same result as with the values themselves.
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160       Unsynchronized accesses
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162       Unsynchronized accesses to weak hash sets are a programming error.  Un‐
163       synchronized  accesses  to  a weak hash set may lead to an invalid weak
164       hash set state. Thus, concurrent accesses to weak  hash  sets  must  be
165       synchronized (for instance with a Mutex.t ).
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167       module type S = sig end
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170       The output signature of the functor Weak.Make .
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173       module Make : functor (H : Hashtbl.HashedType) -> sig end
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176       Functor  building  an  implementation  of  the weak hash set structure.
177       H.equal can't be the physical equality, since only  shallow  copies  of
178       the elements in the set are given to it.
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184OCamldoc                          2023-07-20                    Stdlib.Weak(3)