package ocaml-compiler
Official release of OCaml 5.3.0
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Dune Dependency
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Sources
ocaml-5.3.0.tar.gz
sha256=22c1dd9de21bf43b62d1909041fb5fad648905227bf69550a6a6bef31e654f38
doc/src/stdlib/dynarray.ml.html
Source file dynarray.ml
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(**************************************************************************) (* *) (* OCaml *) (* *) (* Gabriel Scherer, projet Partout, INRIA Paris-Saclay *) (* *) (* Copyright 2022 Institut National de Recherche en Informatique et *) (* en Automatique. *) (* *) (* All rights reserved. This file is distributed under the terms of *) (* the GNU Lesser General Public License version 2.1, with the *) (* special exception on linking described in the file LICENSE. *) (* *) (**************************************************************************) (* {2 The type ['a t]} A dynamic array is represented using a backing array [arr] and a [length]. It behaves as an array of size [length] -- the indices from [0] to [length - 1] included contain user-provided values and can be [get] and [set] -- but the length may also change in the future by adding or removing elements at the end. We use the following concepts; - capacity: the length of the backing array: [Array.length arr] - live space: the portion of the backing array with indices from [0] to [length - 1] included. - empty space: the portion of the backing array from [length] to the end of the backing array. {2 Dummies} We should not keep a user-provided value in the empty space, as this could extend its lifetime and may result in memory leaks of arbitrary size. Functions that remove elements from the dynamic array, such as [pop_last] or [truncate], must really erase the element from the backing array. To do so, we use an unsafe/magical [dummy] in the empty array. This dummy is *not* type-safe, it is not a valid value of type ['a], so we must be very careful never to return it to the user. After accessing any element of the array, we must check that it is not the dummy. In particular, this dummy must be distinct from any other value the user could provide -- we ensure this by using a dynamically-allocated mutable reference as our dummy. {2 Invariants and valid states} We enforce the invariant that [length >= 0] at all times. we rely on this invariant for optimization. The following conditions define what we call a "valid" dynarray: - valid length: [length <= Array.length arr] - no missing element in the live space: forall i, [0 <= i < length] implies [arr.(i) != dummy] - no element in the empty space: forall i, [length <= i < Array.length arr] implies [arr.(i) == dummy] Unfortunately, we cannot easily enforce validity as an invariant in presence of concurrent updates. We can thus observe dynarrays in "invalid states". Our implementation may raise exceptions or return incorrect results on observing invalid states, but of course it must preserve memory safety. {3 Dummies and flat float arrays} OCaml performs a dynamic optimization of the representation of float arrays, which is incompatible with our use of a dummy value: if we initialize an array with user-provided elements, it may get an optimized into a "flat float array", and writing our non-float dummy into it would crash. To avoid interactions between unsafe dummies and flat float arrays, we ensure that the arrays that we use are never initialized with floating point values. In that case we will always get a non-flat array, and storing float values inside those is safe (if less efficient). We call this the 'no-flat-float' invariant. {3 Marshalling dummies} There is a risk of interaction between dummies and marshalling. If we use a global dynamically-allocated dummy for the whole module, we are not robust to a user marshalling a dynarray and unmarshalling it inside another program with a different global dummy. The trick is to store the dummy that we use in the dynarray metadata record. Marshalling the dynarray will then preserve the physical equality between this dummy field and dummy elements in the array, as expected. This reasoning assumes that marshalling does not use the [No_sharing] flag. To ensure that users do not marshal dummies with [No_sharing], we use a recursive/cyclic dummy that would make such marshalling loop forever. (This is not nice, but better than segfaulting later for obscure reasons.) *) (** The [Dummy] module encapsulates the low-level magic we use for dummies, providing a strongly-typed API that: - makes it explicit where dummies are used - makes it hard to mistakenly mix data using distinct dummies, which would be unsound *) module Dummy : sig (** {4 Dummies} *) type 'stamp dummy (** The type of dummies is parametrized by a ['stamp] variable, so that two dummies with different stamps cannot be confused together. *) type fresh_dummy = Fresh : 'stamp dummy -> fresh_dummy val fresh : unit -> fresh_dummy (** The type of [fresh] enforces a fresh/unknown/opaque stamp for the returned dummy, distinct from all previous stamps. *) (** {4 Values or dummies} *) type ('a, 'stamp) with_dummy (** a value of type [('a, 'stamp) with_dummy] is either a proper value of type ['a] or a dummy with stamp ['stamp]. *) val of_val : 'a -> ('a, 'stamp) with_dummy val of_dummy : 'stamp dummy -> ('a, 'stamp) with_dummy val is_dummy : ('a, 'stamp) with_dummy -> 'stamp dummy -> bool val unsafe_get : ('a, 'stamp) with_dummy -> 'a (** [unsafe_get v] can only be called safely if [is_dummy v dummy] is [false]. We could instead provide [val find : ('a, 'stamp) with_dummy -> ('a, 'stamp dummy) result] but this would involve intermediary allocations. {[match find x with | None -> ... | Some v -> ...]} can instead be written {[if Dummy.is_dummy x then ... else let v = Dummy.unsafe_get x in ...]} *) (** {4 Arrays of values or dummies} *) module Array : sig val make : int -> 'a -> dummy:'stamp dummy -> ('a, 'stamp) with_dummy array val init : int -> (int -> 'a) -> dummy:'stamp dummy -> ('a, 'stamp) with_dummy array val copy : 'a array -> dummy:'stamp dummy -> ('a, 'stamp) with_dummy array val unsafe_nocopy : 'a array -> dummy:'stamp dummy -> ('a, 'stamp) with_dummy array (** [unsafe_nocopy] assumes that the input array was created locally and will not be used anymore (in the spirit of [Bytes.unsafe_to_string]), and avoids a copy of the input array when possible. *) val blit_array : 'a array -> int -> ('a, 'stamp) with_dummy array -> int -> len:int -> unit val blit : ('a, 'stamp1) with_dummy array -> 'stamp1 dummy -> int -> ('a, 'stamp2) with_dummy array -> 'stamp2 dummy -> int -> len:int -> unit val prefix : ('a, 'stamp) with_dummy array -> int -> ('a, 'stamp) with_dummy array val extend : ('a, 'stamp) with_dummy array -> length:int -> dummy:'stamp dummy -> new_capacity:int -> ('a, 'stamp) with_dummy array end end = struct (* We want to use a cyclic value so that No_sharing marshalling fails loudly, but we want also comparison of dynarrays to work as expected, and not loop forever. Our approach is to use an object value that contains a cycle. Objects are compared by their unique id, so comparison is not structural and will not loop on the cycle, but marshalled by content, so marshalling without sharing will fail on the cycle. (It is a bit tricky to build an object that does not contain functional values where marshalling fails, see [fresh ()] below for how we do it.) *) type 'stamp dummy = < > type fresh_dummy = Fresh : 'stamp dummy -> fresh_dummy let fresh () = (* dummies and marshalling: we intentionally use a cyclic value here. *) let r = ref None in ignore (* hack: this primitive is required by the object expression below, ensure that 'make depend' notices it. *) CamlinternalOO.create_object_opt; let dummy = object val x = r end in r := Some dummy; Fresh dummy type ('a, 'stamp) with_dummy = 'a let of_val v = v let of_dummy (type a stamp) (dummy : stamp dummy) = (Obj.magic dummy : (a, stamp) with_dummy) let is_dummy v dummy = v == of_dummy dummy let unsafe_get v = v module Array = struct let make n x ~dummy = if Obj.(tag (repr x) <> double_tag) then Array.make n (of_val x) else begin let arr = Array.make n (of_dummy dummy) in Array.fill arr 0 n (of_val x); arr end let copy a ~dummy = if Obj.(tag (repr a) <> double_array_tag) then Array.copy a else begin let n = Array.length a in let arr = Array.make n (of_dummy dummy) in for i = 0 to n - 1 do Array.unsafe_set arr i (of_val (Array.unsafe_get a i)); done; arr end let unsafe_nocopy a ~dummy = if Obj.(tag (repr a) <> double_array_tag) then a else copy a ~dummy let init n f ~dummy = let arr = Array.make n (of_dummy dummy) in for i = 0 to n - 1 do Array.unsafe_set arr i (of_val (f i)) done; arr let blit_array src src_pos dst dst_pos ~len = if Obj.(tag (repr src) <> double_array_tag) then Array.blit src src_pos dst dst_pos len else begin for i = 0 to len - 1 do dst.(dst_pos + i) <- of_val src.(src_pos + i) done; end let blit src src_dummy src_pos dst dst_dummy dst_pos ~len = if src_dummy == dst_dummy then Array.blit src src_pos dst dst_pos len else begin if len < 0 || src_pos < 0 || src_pos + len < 0 (* overflow check *) || src_pos + len > Array.length src || dst_pos < 0 || dst_pos + len < 0 (* overflow check *) || dst_pos + len > Array.length dst then begin (* We assume that the caller has already checked this and will raise a proper error. The check here is only for memory safety, it should not be reached and it is okay if the error is uninformative. *) assert false; end; (* We failed the check [src_dummy == dst_dummy] above, so we know that in fact [src != dst] -- two dynarrays with distinct dummies cannot share the same backing arrays. *) assert (src != dst); (* In particular, the source and destination arrays cannot overlap, so we can always copy in ascending order without risking overwriting an element needed later. *) for i = 0 to len - 1 do Array.unsafe_set dst (dst_pos + i) (Array.unsafe_get src (src_pos + i)); done end let prefix arr n = (* Note: the safety of the [Array.sub] call below, with respect to our 'no-flat-float' invariant, relies on the fact that [Array.sub] checks the tag of the input array, not whether the elements themselves are float. To avoid relying on this undocumented property we could use [Array.make length dummy] and then set values in a loop, but this would result in [caml_modify] rather than [caml_initialize]. *) Array.sub arr 0 n let extend arr ~length ~dummy ~new_capacity = (* 'no-flat-float' invariant: we initialise the array with our non-float dummy to get a non-flat array. *) let new_arr = Array.make new_capacity (of_dummy dummy) in Array.blit arr 0 new_arr 0 length; new_arr end end type 'a t = Pack : ('a, 'stamp) t_ -> 'a t [@@unboxed] and ('a, 'stamp) t_ = { mutable length : int; mutable arr : ('a, 'stamp) Dummy.with_dummy array; dummy : 'stamp Dummy.dummy; } let global_dummy = Dummy.fresh () (* We need to ensure that dummies are never exposed to the user as values of type ['a]. Including the dummy in the dynarray metadata is necessary for marshalling to behave correctly, but there is no obligation to create a fresh dummy for each new dynarray, we can use a global dummy. On the other hand, unmarshalling may precisely return a dynarray with another dummy: we cannot assume that all dynarrays use this global dummy. The existential hiding of the dummy ['stamp] parameter helps us to avoid this assumption. *) module Error = struct let[@inline never] index_out_of_bounds f ~i ~length = if length = 0 then Printf.ksprintf invalid_arg "Dynarray.%s: index %d out of bounds (empty dynarray)" f i else Printf.ksprintf invalid_arg "Dynarray.%s: index %d out of bounds (0..%d)" f i (length - 1) let[@inline never] negative_length_requested f n = Printf.ksprintf invalid_arg "Dynarray.%s: negative length %d requested" f n let[@inline never] negative_capacity_requested f n = Printf.ksprintf invalid_arg "Dynarray.%s: negative capacity %d requested" f n let[@inline never] requested_length_out_of_bounds f requested_length = Printf.ksprintf invalid_arg "Dynarray.%s: cannot grow to requested length %d (max_array_length is %d)" f requested_length Sys.max_array_length (* When observing an invalid state ([missing_element], [invalid_length]), we do not give the name of the calling function in the error message, as the error is related to invalid operations performed earlier, and not to the callsite of the function itself. *) let invalid_state_description = "Invalid dynarray (unsynchronized concurrent length change)" let[@inline never] missing_element ~i ~length = Printf.ksprintf invalid_arg "%s: missing element at position %d < length %d" invalid_state_description i length let[@inline never] invalid_length ~length ~capacity = Printf.ksprintf invalid_arg "%s: length %d > capacity %d" invalid_state_description length capacity let[@inline never] length_change_during_iteration f ~expected ~observed = Printf.ksprintf invalid_arg "Dynarray.%s: a length change from %d to %d occurred during iteration" f expected observed (* When an [Empty] element is observed unexpectedly at index [i], it may be either an out-of-bounds access or an invalid-state situation depending on whether [i <= length]. *) let[@inline never] unexpected_empty_element f ~i ~length = if i < length then missing_element ~i ~length else index_out_of_bounds f ~i ~length let[@inline never] empty_dynarray f = Printf.ksprintf invalid_arg "Dynarray.%s: empty array" f end (* Detecting iterator invalidation. See {!iter} below for a detailed usage example. *) let check_same_length f (Pack a) ~length = let length_a = a.length in if length <> length_a then Error.length_change_during_iteration f ~expected:length ~observed:length_a (** Careful unsafe access. *) (* Postcondition on non-exceptional return: [length <= Array.length arr] *) let[@inline always] check_valid_length length arr = let capacity = Array.length arr in if length > capacity then Error.invalid_length ~length ~capacity (* Precondition: [0 <= i < length <= Array.length arr] This precondition is typically guaranteed by knowing [0 <= i < length] and calling [check_valid_length length arr].*) let[@inline always] unsafe_get arr ~dummy ~i ~length = let v = Array.unsafe_get arr i in if Dummy.is_dummy v dummy then Error.missing_element ~i ~length else Dummy.unsafe_get v (** {1:dynarrays Dynamic arrays} *) let create () = let Dummy.Fresh dummy = global_dummy in Pack { length = 0; arr = [| |]; dummy = dummy; } let make n x = if n < 0 then Error.negative_length_requested "make" n; let Dummy.Fresh dummy = global_dummy in let arr = Dummy.Array.make n x ~dummy in Pack { length = n; arr; dummy; } let init (type a) n (f : int -> a) : a t = if n < 0 then Error.negative_length_requested "init" n; let Dummy.Fresh dummy = global_dummy in let arr = Dummy.Array.init ~dummy n f in Pack { length = n; arr; dummy; } let get (type a) (Pack a : a t) i = (* This implementation will propagate an [Invalid_argument] exception from array lookup if the index is out of the backing array, instead of using our own [Error.index_out_of_bounds]. This is allowed by our specification, and more efficient -- no need to check that [length a <= capacity a] in the fast path. *) let v = a.arr.(i) in if Dummy.is_dummy v a.dummy then Error.unexpected_empty_element "get" ~i ~length:a.length else Dummy.unsafe_get v let set (Pack a) i x = let {arr; length; _} = a in if i >= length then Error.index_out_of_bounds "set" ~i ~length else arr.(i) <- Dummy.of_val x let length (Pack a) = a.length let is_empty (Pack a) = (a.length = 0) let copy (type a) (Pack {length; arr; dummy} : a t) : a t = check_valid_length length arr; (* use [length] as the new capacity to make this an O(length) operation. *) let arr = Dummy.Array.prefix arr length in Pack { length; arr; dummy } let get_last (Pack a) = let {arr; length; dummy} = a in check_valid_length length arr; (* We know [length <= capacity a]. *) if length = 0 then Error.empty_dynarray "get_last"; (* We know [length > 0]. *) unsafe_get arr ~dummy ~i:(length - 1) ~length let find_last (Pack a) = let {arr; length; dummy} = a in check_valid_length length arr; (* We know [length <= capacity a]. *) if length = 0 then None else (* We know [length > 0]. *) Some (unsafe_get arr ~dummy ~i:(length - 1) ~length) (** {1:removing Removing elements} *) let pop_last (Pack a) = let {arr; length; dummy} = a in check_valid_length length arr; (* We know [length <= capacity a]. *) if length = 0 then raise Not_found; let last = length - 1 in (* We know [length > 0] so [last >= 0]. *) let v = unsafe_get arr ~dummy ~i:last ~length in Array.unsafe_set arr last (Dummy.of_dummy dummy); a.length <- last; v let pop_last_opt a = match pop_last a with | exception Not_found -> None | x -> Some x let remove_last (Pack a) = let last = a.length - 1 in if last >= 0 then begin a.length <- last; a.arr.(last) <- Dummy.of_dummy a.dummy; end let truncate (Pack a) n = if n < 0 then Error.negative_length_requested "truncate" n; let {arr; length; dummy} = a in if length <= n then () else begin a.length <- n; Array.fill arr n (length - n) (Dummy.of_dummy dummy) end let clear a = truncate a 0 (** {1:capacity Backing array and capacity} *) let capacity (Pack a) = Array.length a.arr let next_capacity n = let n' = (* For large values of n, we use 1.5 as our growth factor. For smaller values of n, we grow more aggressively to avoid reallocating too much when accumulating elements into an empty array. The constants "512 words" and "8 words" below are taken from https://github.com/facebook/folly/blob/ c06c0f41d91daf1a6a5f3fc1cd465302ac260459/folly/FBVector.h#L1128-L1157 *) if n <= 512 then n * 2 else n + n / 2 in (* jump directly from 0 to 8 *) min (max 8 n') Sys.max_array_length let ensure_capacity (Pack a) capacity_request = let arr = a.arr in let cur_capacity = Array.length arr in if capacity_request < 0 then Error.negative_capacity_requested "ensure_capacity" capacity_request else if cur_capacity >= capacity_request then (* This is the fast path, the code up to here must do as little as possible. (This is why we don't use [let {arr; length} = a] as usual, the length is not needed in the fast path.)*) () else begin if capacity_request > Sys.max_array_length then Error.requested_length_out_of_bounds "ensure_capacity" capacity_request; let new_capacity = (* We use either the next exponential-growth strategy, or the requested strategy, whichever is bigger. Compared to only using the exponential-growth strategy, this lets us use less memory by avoiding any overshoot whenever the capacity request is noticeably larger than the current capacity. Compared to only using the requested capacity, this avoids losing the amortized guarantee: we allocated "exponentially or more", so the amortization holds. In particular, notice that repeated calls to [ensure_capacity a (length a + 1)] will have amortized-linear rather than quadratic complexity. *) max (next_capacity cur_capacity) capacity_request in assert (new_capacity > 0); let new_arr = Dummy.Array.extend arr ~length:a.length ~dummy:a.dummy ~new_capacity in a.arr <- new_arr; (* postcondition: *) assert (0 <= capacity_request); assert (capacity_request <= Array.length new_arr); end let ensure_extra_capacity a extra_capacity_request = ensure_capacity a (length a + extra_capacity_request) let fit_capacity (Pack a) = if Array.length a.arr = a.length then () else a.arr <- Dummy.Array.prefix a.arr a.length let set_capacity (Pack a) n = if n < 0 then Error.negative_capacity_requested "set_capacity" n; let arr = a.arr in let cur_capacity = Array.length arr in if n < cur_capacity then begin a.length <- min a.length n; a.arr <- Dummy.Array.prefix arr n; end else if n > cur_capacity then begin a.arr <- Dummy.Array.extend arr ~length:a.length ~dummy:a.dummy ~new_capacity:n; end let reset (Pack a) = a.length <- 0; a.arr <- [||] (** {1:adding Adding elements} *) (* We chose an implementation of [add_last a x] that behaves correctly in presence of asynchronous / re-entrant code execution around allocations and poll points: if another thread or a callback gets executed on allocation, we add the element at the new end of the dynamic array. (We do not give the same guarantees in presence of concurrent parallel updates, which are much more expensive to protect against.) *) (* [add_last_if_room a v] only writes the value if there is room, and returns [false] otherwise. *) let[@inline] add_last_if_room (Pack a) v = let {arr; length; _} = a in (* we know [0 <= length] *) if length >= Array.length arr then false else begin (* we know [0 <= length < Array.length arr] *) a.length <- length + 1; Array.unsafe_set arr length (Dummy.of_val v); true end let add_last a x = if add_last_if_room a x then () else begin (* slow path *) let rec grow_and_add a x = ensure_extra_capacity a 1; if not (add_last_if_room a x) then grow_and_add a x in grow_and_add a x end let rec append_list a li = match li with | [] -> () | x :: xs -> add_last a x; append_list a xs let append_iter a iter b = iter (fun x -> add_last a x) b let append_seq a seq = Seq.iter (fun x -> add_last a x) seq (* blitting *) let blit_assume_room (Pack src) src_pos src_length (Pack dst) dst_pos dst_length blit_length = (* The caller of [blit_assume_room] typically calls [ensure_capacity] right before. This could run asynchronous code. We want to fail reliably on any asynchronous length change, as it may invalidate the source and target ranges provided by the user. So we double-check that the lengths have not changed. *) let src_arr = src.arr in let dst_arr = dst.arr in check_same_length "blit" (Pack src) ~length:src_length; check_same_length "blit" (Pack dst) ~length:dst_length; if dst_pos + blit_length > dst_length then begin dst.length <- dst_pos + blit_length; end; (* note: [src] and [dst] may be equal when self-blitting, so [src.length] may have been mutated here. *) Dummy.Array.blit src_arr src.dummy src_pos dst_arr dst.dummy dst_pos ~len:blit_length let blit ~src ~src_pos ~dst ~dst_pos ~len = let src_length = length src in let dst_length = length dst in if len < 0 then Printf.ksprintf invalid_arg "Dynarray.blit: invalid blit length (%d)" len; if src_pos < 0 || src_pos + len > src_length then Printf.ksprintf invalid_arg "Dynarray.blit: invalid source region (%d..%d) \ in source dynarray of length %d" src_pos (src_pos + len) src_length; if dst_pos < 0 || dst_pos > dst_length then Printf.ksprintf invalid_arg "Dynarray.blit: invalid target region (%d..%d) \ in target dynarray of length %d" dst_pos (dst_pos + len) dst_length; ensure_capacity dst (dst_pos + len); blit_assume_room src src_pos src_length dst dst_pos dst_length len (* append_array: same [..._if_room] and loop logic as [add_last]. *) let append_array_if_room (Pack a) b = let {arr; length = length_a; _} = a in let length_b = Array.length b in if length_a + length_b > Array.length arr then false else begin (* Note: we intentionally update the length *before* filling the elements. This "reserve before fill" approach provides better behavior than "fill then notify" in presence of reentrant modifications (which may occur on [blit] below): - If some code asynchronously adds new elements after this length update, they will go after the space we just reserved, and in particular no addition will be lost. If instead we updated the length after the loop, any asynchronous addition during the loop could be erased or erase one of our additions, silently, without warning the user. - If some code asynchronously iterates on the dynarray, or removes elements, or otherwise tries to access the reserved-but-not-yet-filled space, it will get a clean "missing element" error. This is worse than with the fill-then-notify approach where the new elements would only become visible (to iterators, for removal, etc.) altogether at the end of loop. To summarise, "reserve before fill" is better on add-add races, and "fill then notify" is better on add-remove or add-iterate races. But the key difference is the failure mode: reserve-before fails on add-remove or add-iterate races with a clean error, while notify-after fails on add-add races with silently disappearing data. *) a.length <- length_a + length_b; Dummy.Array.blit_array b 0 arr length_a ~len:length_b; true end let append_array a b = if append_array_if_room a b then () else begin (* slow path *) let rec grow_and_append a b = ensure_extra_capacity a (Array.length b); if not (append_array_if_room a b) then grow_and_append a b in grow_and_append a b end (* append: same [..._if_room] and loop logic as [add_last]. *) (* It is a programming error to mutate the length of [b] during a call to [append a b]. To detect this mistake we keep track of the length of [b] throughout the computation and check it that does not change. *) let append_if_room (Pack a) b ~length_b = let {arr = arr_a; length = length_a; _} = a in if length_a + length_b > Array.length arr_a then false else begin (* blit [0..length_b-1] into [length_a..length_a+length_b-1]. *) blit_assume_room b 0 length_b (Pack a) length_a length_a length_b; check_same_length "append" b ~length:length_b; true end let append a b = let length_b = length b in if append_if_room a b ~length_b then () else begin (* slow path *) let rec grow_and_append a b ~length_b = ensure_extra_capacity a length_b; (* Eliding the [check_same_length] call below would be wrong in the case where [a] and [b] are aliases of each other, we would get into an infinite loop instead of failing. We could push the call to [append_if_room] itself, but we prefer to keep it in the slow path. *) check_same_length "append" b ~length:length_b; if not (append_if_room a b ~length_b) then grow_and_append a b ~length_b in grow_and_append a b ~length_b end (** {1:iteration Iteration} *) (* The implementation choice that we made for iterators is the one that maximizes efficiency by avoiding repeated bound checking: we check the length of the dynamic array once at the beginning, and then only operate on that portion of the dynarray, ignoring elements added in the meantime. The specification states that it is a programming error to mutate the length of the array during iteration. We check for this and raise an error on size change. Note that we may still miss some transient state changes that cancel each other and leave the length unchanged at the next check. *) let iter_ f k a = let Pack {arr; length; dummy} = a in (* [check_valid_length length arr] is used for memory safety, it guarantees that the backing array has capacity at least [length], allowing unsafe array access. [check_same_length] is used for correctness, it lets the function fail more often if we discover the programming error of mutating the length during iteration. We could, naively, call [check_same_length] at each iteration of the loop (before or after, or both). However, notice that this is not necessary to detect the removal of elements from [a]: if elements have been removed by the time the [for] loop reaches them, then [unsafe_get] will itself fail with an [Invalid_argument] exception. We only need to detect the addition of new elements to [a] during iteration, and for this it is enough to call [check_same_length] once at the end. Calling [check_same_length] more often could catch more programming errors, but the only errors that we miss with this optimization are those that keep the array size constant -- additions and deletions that cancel each other. We consider this an acceptable tradeoff. *) check_valid_length length arr; for i = 0 to length - 1 do k (unsafe_get arr ~dummy ~i ~length); done; check_same_length f a ~length let iter k a = iter_ "iter" k a let iteri k a = let Pack {arr; length; dummy} = a in check_valid_length length arr; for i = 0 to length - 1 do k i (unsafe_get arr ~i ~dummy ~length); done; check_same_length "iteri" a ~length let map f a = let Pack {arr = arr_in; length; dummy} = a in check_valid_length length arr_in; let arr_out = Array.make length (Dummy.of_dummy dummy) in for i = 0 to length - 1 do Array.unsafe_set arr_out i (Dummy.of_val (f (unsafe_get arr_in ~dummy ~i ~length))) done; let res = Pack { length; arr = arr_out; dummy; } in check_same_length "map" a ~length; res let mapi f a = let Pack {arr = arr_in; length; dummy} = a in check_valid_length length arr_in; let arr_out = Array.make length (Dummy.of_dummy dummy) in for i = 0 to length - 1 do Array.unsafe_set arr_out i (Dummy.of_val (f i (unsafe_get arr_in ~dummy ~i ~length))) done; let res = Pack { length; arr = arr_out; dummy; } in check_same_length "mapi" a ~length; res let fold_left f acc a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let r = ref acc in for i = 0 to length - 1 do let v = unsafe_get arr ~dummy ~i ~length in r := f !r v; done; check_same_length "fold_left" a ~length; !r let fold_right f a acc = let Pack {arr; length; dummy} = a in check_valid_length length arr; let r = ref acc in for i = length - 1 downto 0 do let v = unsafe_get arr ~dummy ~i ~length in r := f v !r; done; check_same_length "fold_right" a ~length; !r let exists p a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let rec loop p arr dummy i length = if i = length then false else p (unsafe_get arr ~dummy ~i ~length) || loop p arr dummy (i + 1) length in let res = loop p arr dummy 0 length in check_same_length "exists" a ~length; res let for_all p a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let rec loop p arr dummy i length = if i = length then true else p (unsafe_get arr ~dummy ~i ~length) && loop p arr dummy (i + 1) length in let res = loop p arr dummy 0 length in check_same_length "for_all" a ~length; res let filter f a = let b = create () in iter_ "filter" (fun x -> if f x then add_last b x) a; b let filter_map f a = let b = create () in iter_ "filter_map" (fun x -> match f x with | None -> () | Some y -> add_last b y ) a; b let mem x a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let rec loop i = if i = length then false else if Stdlib.compare (unsafe_get arr ~dummy ~i ~length) x = 0 then true else loop (succ i) in let res = loop 0 in check_same_length "mem" a ~length; res let memq x a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let rec loop i = if i = length then false else if (unsafe_get arr ~dummy ~i ~length) == x then true else loop (succ i) in let res = loop 0 in check_same_length "memq" a ~length; res let find_opt p a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let rec loop i = if i = length then None else let x = unsafe_get arr ~dummy ~i ~length in if p x then Some x else loop (succ i) in let res = loop 0 in check_same_length "find_opt" a ~length; res let find_index p a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let rec loop i = if i = length then None else let x = unsafe_get arr ~dummy ~i ~length in if p x then Some i else loop (succ i) in let res = loop 0 in check_same_length "find_index" a ~length; res let find_map p a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let rec loop i = if i = length then None else match p (unsafe_get arr ~dummy ~i ~length) with | None -> loop (succ i) | Some _ as r -> r in let res = loop 0 in check_same_length "find_map" a ~length; res let find_mapi p a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let rec loop i = if i = length then None else match p i (unsafe_get arr ~dummy ~i ~length) with | None -> loop (succ i) | Some _ as r -> r in let res = loop 0 in check_same_length "find_mapi" a ~length; res let equal eq a1 a2 = let Pack {arr = arr1; length = length; dummy = dum1} = a1 in let Pack {arr = arr2; length = len2; dummy = dum2} = a2 in if length <> len2 then false else begin check_valid_length length arr1; check_valid_length length arr2; let rec loop i = if i = length then true else eq (unsafe_get arr1 ~dummy:dum1 ~i ~length) (unsafe_get arr2 ~dummy:dum2 ~i ~length) && loop (i + 1) in let r = loop 0 in check_same_length "equal" a1 ~length; check_same_length "equal" a2 ~length; r end let compare cmp a1 a2 = let Pack {arr = arr1; length = length; dummy = dum1} = a1 in let Pack {arr = arr2; length = len2; dummy = dum2} = a2 in if length <> len2 then length - len2 else begin check_valid_length length arr1; check_valid_length length arr2; let rec loop i = if i = length then 0 else let c = cmp (unsafe_get arr1 ~dummy:dum1 ~i ~length) (unsafe_get arr2 ~dummy:dum2 ~i ~length) in if c <> 0 then c else loop (i + 1) in let r = loop 0 in check_same_length "compare" a1 ~length; check_same_length "compare" a2 ~length; r end (** {1:conversions Conversions to other data structures} *) (* The eager [to_*] conversion functions behave similarly to iterators in presence of updates during computation. The [*_reentrant] functions obey their more permissive specification, which tolerates any concurrent update. *) let of_array a = let length = Array.length a in let Dummy.Fresh dummy = global_dummy in let arr = Dummy.Array.copy a ~dummy in Pack { length; arr; dummy; } let to_array a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let res = Array.init length (fun i -> unsafe_get arr ~dummy ~i ~length ) in check_same_length "to_array" a ~length; res let of_list li = let a = Array.of_list li in let length = Array.length a in let Dummy.Fresh dummy = global_dummy in let arr = Dummy.Array.unsafe_nocopy a ~dummy in Pack { length; arr; dummy; } let to_list a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let l = ref [] in for i = length - 1 downto 0 do l := unsafe_get arr ~dummy ~i ~length :: !l done; check_same_length "to_list" a ~length; !l let of_seq seq = let init = create() in append_seq init seq; init let to_seq a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let rec aux i = fun () -> check_same_length "to_seq" a ~length; if i >= length then Seq.Nil else begin let v = unsafe_get arr ~dummy ~i ~length in Seq.Cons (v, aux (i + 1)) end in aux 0 let to_seq_reentrant a = let rec aux i = fun () -> if i >= length a then Seq.Nil else begin let v = get a i in Seq.Cons (v, aux (i + 1)) end in aux 0 let to_seq_rev a = let Pack {arr; length; dummy} = a in check_valid_length length arr; let rec aux i = fun () -> check_same_length "to_seq_rev" a ~length; if i < 0 then Seq.Nil else begin let v = unsafe_get arr ~dummy ~i ~length in Seq.Cons (v, aux (i - 1)) end in aux (length - 1) let to_seq_rev_reentrant a = let rec aux i = fun () -> if i < 0 then Seq.Nil else if i >= length a then (* If some elements have been removed in the meantime, we skip those elements and continue with the new end of the array. *) aux (length a - 1) () else begin let v = get a i in Seq.Cons (v, aux (i - 1)) end in aux (length a - 1)
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