1StdLabels.Bytes(3) OCaml library StdLabels.Bytes(3)
2
6 StdLabels.Bytes - no description
7
9 Module StdLabels.Bytes
10
12 Module Bytes
13 : (module BytesLabels)
14 val length : bytes -> int
23 Return the length (number of bytes) of the argument.
25 val get : bytes -> int -> char
29 get s n returns the byte at index n in argument s .
32 Raises Invalid_argument if n is not a valid index in s .
35 val set : bytes -> int -> char -> unit
39 set s n c modifies s in place, replacing the byte at index n with c .
42 Raises Invalid_argument if n is not a valid index in s .
45 val create : int -> bytes
49 create n returns a new byte sequence of length n . The sequence is
52 uninitialized and contains arbitrary bytes.
53 Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
56 val make : int -> char -> bytes
60 make n c returns a new byte sequence of length n , filled with the byte
63 c .
64 Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
67 val init : int -> f:(int -> char) -> bytes
71 init n f returns a fresh byte sequence of length n , with character i
74 initialized to the result of f i (in increasing index order).
75 Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
78 val empty : bytes
82 A byte sequence of size 0.
84 val copy : bytes -> bytes
88 Return a new byte sequence that contains the same bytes as the argu‐
90 ment.
91 val of_string : string -> bytes
95 Return a new byte sequence that contains the same bytes as the given
97 string.
98 val to_string : bytes -> string
102 Return a new string that contains the same bytes as the given byte se‐
104 quence.
105 val sub : bytes -> pos:int -> len:int -> bytes
109 sub s ~pos ~len returns a new byte sequence of length len , containing
112 the subsequence of s that starts at position pos and has length len .
113 Raises Invalid_argument if pos and len do not designate a valid range
116 of s .
117 val sub_string : bytes -> pos:int -> len:int -> string
121 Same as BytesLabels.sub but return a string instead of a byte sequence.
123 val extend : bytes -> left:int -> right:int -> bytes
127 extend s ~left ~right returns a new byte sequence that contains the
130 bytes of s , with left uninitialized bytes prepended and right unini‐
131 tialized bytes appended to it. If left or right is negative, then bytes
132 are removed (instead of appended) from the corresponding side of s .
133 Since 4.05.0 in BytesLabels
136 Raises Invalid_argument if the result length is negative or longer than
139 Sys.max_string_length bytes.
140 val fill : bytes -> pos:int -> len:int -> char -> unit
144 fill s ~pos ~len c modifies s in place, replacing len characters with c
147 , starting at pos .
148 Raises Invalid_argument if pos and len do not designate a valid range
151 of s .
152 val blit : src:bytes -> src_pos:int -> dst:bytes -> dst_pos:int ->
156 len:int -> unit
157 blit ~src ~src_pos ~dst ~dst_pos ~len copies len bytes from sequence
160 src , starting at index src_pos , to sequence dst , starting at index
161 dst_pos . It works correctly even if src and dst are the same byte se‐
162 quence, and the source and destination intervals overlap.
163 Raises Invalid_argument if src_pos and len do not designate a valid
166 range of src , or if dst_pos and len do not designate a valid range of
167 dst .
168 val blit_string : src:string -> src_pos:int -> dst:bytes -> dst_pos:int
172 -> len:int -> unit
173 blit ~src ~src_pos ~dst ~dst_pos ~len copies len bytes from string src
176 , starting at index src_pos , to byte sequence dst , starting at index
177 dst_pos .
178 Since 4.05.0 in BytesLabels
181 Raises Invalid_argument if src_pos and len do not designate a valid
184 range of src , or if dst_pos and len do not designate a valid range of
185 dst .
186 val concat : sep:bytes -> bytes list -> bytes
190 concat ~sep sl concatenates the list of byte sequences sl , inserting
193 the separator byte sequence sep between each, and returns the result as
194 a new byte sequence.
195 Raises Invalid_argument if the result is longer than
198 Sys.max_string_length bytes.
199 val cat : bytes -> bytes -> bytes
203 cat s1 s2 concatenates s1 and s2 and returns the result as a new byte
206 sequence.
207 Since 4.05.0 in BytesLabels
210 Raises Invalid_argument if the result is longer than
213 Sys.max_string_length bytes.
214 val iter : f:(char -> unit) -> bytes -> unit
218 iter ~f s applies function f in turn to all the bytes of s . It is
221 equivalent to f (get s 0); f (get s 1); ...; f (get s
222 (length s - 1)); () .
223 val iteri : f:(int -> char -> unit) -> bytes -> unit
227 Same as BytesLabels.iter , but the function is applied to the index of
229 the byte as first argument and the byte itself as second argument.
230 val map : f:(char -> char) -> bytes -> bytes
234 map ~f s applies function f in turn to all the bytes of s (in increas‐
237 ing index order) and stores the resulting bytes in a new sequence that
238 is returned as the result.
239 val mapi : f:(int -> char -> char) -> bytes -> bytes
243 mapi ~f s calls f with each character of s and its index (in increasing
246 index order) and stores the resulting bytes in a new sequence that is
247 returned as the result.
248 val fold_left : f:('a -> char -> 'a) -> init:'a -> bytes -> 'a
252 fold_left f x s computes f (... (f (f x (get s 0)) (get s 1)) ...) (get
255 s (n-1)) , where n is the length of s .
256 Since 4.13.0
259 val fold_right : f:(char -> 'a -> 'a) -> bytes -> init:'a -> 'a
263 fold_right f s x computes f (get s 0) (f (get s 1) ( ... (f (get s
266 (n-1)) x) ...)) , where n is the length of s .
267 Since 4.13.0
270 val for_all : f:(char -> bool) -> bytes -> bool
274 for_all p s checks if all characters in s satisfy the predicate p .
277 Since 4.13.0
280 val exists : f:(char -> bool) -> bytes -> bool
284 exists p s checks if at least one character of s satisfies the predi‐
287 cate p .
288 Since 4.13.0
291 val trim : bytes -> bytes
295 Return a copy of the argument, without leading and trailing whitespace.
297 The bytes regarded as whitespace are the ASCII characters ' ' , '\012'
298 , '\n' , '\r' , and '\t' .
299 val escaped : bytes -> bytes
303 Return a copy of the argument, with special characters represented by
305 escape sequences, following the lexical conventions of OCaml. All
306 characters outside the ASCII printable range (32..126) are escaped, as
307 well as backslash and double-quote.
308 Raises Invalid_argument if the result is longer than
311 Sys.max_string_length bytes.
312 val index : bytes -> char -> int
316 index s c returns the index of the first occurrence of byte c in s .
319 Raises Not_found if c does not occur in s .
322 val index_opt : bytes -> char -> int option
326 index_opt s c returns the index of the first occurrence of byte c in s
329 or None if c does not occur in s .
330 Since 4.05
333 val rindex : bytes -> char -> int
337 rindex s c returns the index of the last occurrence of byte c in s .
340 Raises Not_found if c does not occur in s .
343 val rindex_opt : bytes -> char -> int option
347 rindex_opt s c returns the index of the last occurrence of byte c in s
350 or None if c does not occur in s .
351 Since 4.05
354 val index_from : bytes -> int -> char -> int
358 index_from s i c returns the index of the first occurrence of byte c in
361 s after position i . index s c is equivalent to index_from s 0 c .
362 Raises Invalid_argument if i is not a valid position in s .
365 Raises Not_found if c does not occur in s after position i .
368 val index_from_opt : bytes -> int -> char -> int option
372 index_from_opt s i c returns the index of the first occurrence of byte
375 c in s after position i or None if c does not occur in s after position
376 i . index_opt s c is equivalent to index_from_opt s 0 c .
377 Since 4.05
380 Raises Invalid_argument if i is not a valid position in s .
383 val rindex_from : bytes -> int -> char -> int
387 rindex_from s i c returns the index of the last occurrence of byte c in
390 s before position i+1 . rindex s c is equivalent to rindex_from s
391 (length s - 1) c .
392 Raises Invalid_argument if i+1 is not a valid position in s .
395 Raises Not_found if c does not occur in s before position i+1 .
398 val rindex_from_opt : bytes -> int -> char -> int option
402 rindex_from_opt s i c returns the index of the last occurrence of byte
405 c in s before position i+1 or None if c does not occur in s before po‐
406 sition i+1 . rindex_opt s c is equivalent to rindex_from s (length s -
407 1) c .
408 Since 4.05
411 Raises Invalid_argument if i+1 is not a valid position in s .
414 val contains : bytes -> char -> bool
418 contains s c tests if byte c appears in s .
421 val contains_from : bytes -> int -> char -> bool
425 contains_from s start c tests if byte c appears in s after position
428 start . contains s c is equivalent to contains_from
429 s 0 c .
430 Raises Invalid_argument if start is not a valid position in s .
433 val rcontains_from : bytes -> int -> char -> bool
437 rcontains_from s stop c tests if byte c appears in s before position
440 stop+1 .
441 Raises Invalid_argument if stop < 0 or stop+1 is not a valid position
444 in s .
445 val uppercase_ascii : bytes -> bytes
449 Return a copy of the argument, with all lowercase letters translated to
451 uppercase, using the US-ASCII character set.
452 Since 4.05.0
455 val lowercase_ascii : bytes -> bytes
459 Return a copy of the argument, with all uppercase letters translated to
461 lowercase, using the US-ASCII character set.
462 Since 4.05.0
465 val capitalize_ascii : bytes -> bytes
469 Return a copy of the argument, with the first character set to upper‐
471 case, using the US-ASCII character set.
472 Since 4.05.0
475 val uncapitalize_ascii : bytes -> bytes
479 Return a copy of the argument, with the first character set to lower‐
481 case, using the US-ASCII character set.
482 Since 4.05.0
485 type t = bytes
488 An alias for the type of byte sequences.
491 val compare : t -> t -> int
495 The comparison function for byte sequences, with the same specification
497 as compare . Along with the type t , this function compare allows the
498 module Bytes to be passed as argument to the functors Set.Make and
499 Map.Make .
500 val equal : t -> t -> bool
504 The equality function for byte sequences.
506 Since 4.05.0
509 val starts_with : prefix:bytes -> bytes -> bool
513 starts_with ~prefix s is true if and only if s starts with prefix .
516 Since 4.13.0
519 val ends_with : suffix:bytes -> bytes -> bool
523 ends_with ~suffix s is true if and only if s ends with suffix .
526 Since 4.13.0
529 Unsafe conversions (for advanced users)
534 This section describes unsafe, low-level conversion functions between
535 bytes and string . They do not copy the internal data; used improperly,
536 they can break the immutability invariant on strings provided by the
537 -safe-string option. They are available for expert library authors, but
538 for most purposes you should use the always-correct BytesLa‐
539 bels.to_string and BytesLabels.of_string instead.
540 val unsafe_to_string : bytes -> string
542 Unsafely convert a byte sequence into a string.
544 To reason about the use of unsafe_to_string , it is convenient to con‐
546 sider an "ownership" discipline. A piece of code that manipulates some
547 data "owns" it; there are several disjoint ownership modes, including:
548 -Unique ownership: the data may be accessed and mutated
550 -Shared ownership: the data has several owners, that may only access
552 it, not mutate it.
553 Unique ownership is linear: passing the data to another piece of code
555 means giving up ownership (we cannot write the data again). A unique
556 owner may decide to make the data shared (giving up mutation rights on
557 it), but shared data may not become uniquely-owned again.
558 unsafe_to_string s can only be used when the caller owns the byte se‐
561 quence s -- either uniquely or as shared immutable data. The caller
562 gives up ownership of s , and gains ownership of the returned string.
563 There are two valid use-cases that respect this ownership discipline:
565 1. Creating a string by initializing and mutating a byte sequence that
567 is never changed after initialization is performed.
568 let string_init len f : string =
571 let s = Bytes.create len in
572 for i = 0 to len - 1 do Bytes.set s i (f i) done;
573 Bytes.unsafe_to_string s
574 This function is safe because the byte sequence s will never be ac‐
577 cessed or mutated after unsafe_to_string is called. The string_init
578 code gives up ownership of s , and returns the ownership of the result‐
579 ing string to its caller.
580 Note that it would be unsafe if s was passed as an additional parameter
582 to the function f as it could escape this way and be mutated in the fu‐
583 ture -- string_init would give up ownership of s to pass it to f , and
584 could not call unsafe_to_string safely.
585 We have provided the String.init , String.map and String.mapi functions
587 to cover most cases of building new strings. You should prefer those
588 over to_string or unsafe_to_string whenever applicable.
589 2. Temporarily giving ownership of a byte sequence to a function that
591 expects a uniquely owned string and returns ownership back, so that we
592 can mutate the sequence again after the call ended.
593 let bytes_length (s : bytes) =
596 String.length (Bytes.unsafe_to_string s)
597 In this use-case, we do not promise that s will never be mutated after
600 the call to bytes_length s . The String.length function temporarily
601 borrows unique ownership of the byte sequence (and sees it as a string
602 ), but returns this ownership back to the caller, which may assume that
603 s is still a valid byte sequence after the call. Note that this is only
604 correct because we know that String.length does not capture its argu‐
605 ment -- it could escape by a side-channel such as a memoization combi‐
606 nator.
607 The caller may not mutate s while the string is borrowed (it has tempo‐
609 rarily given up ownership). This affects concurrent programs, but also
610 higher-order functions: if String.length returned a closure to be
611 called later, s should not be mutated until this closure is fully ap‐
612 plied and returns ownership.
613 val unsafe_of_string : string -> bytes
617 Unsafely convert a shared string to a byte sequence that should not be
619 mutated.
620 The same ownership discipline that makes unsafe_to_string correct ap‐
622 plies to unsafe_of_string : you may use it if you were the owner of the
623 string value, and you will own the return bytes in the same mode.
624 In practice, unique ownership of string values is extremely difficult
626 to reason about correctly. You should always assume strings are shared,
627 never uniquely owned.
628 For example, string literals are implicitly shared by the compiler, so
630 you never uniquely own them.
631 let incorrect = Bytes.unsafe_of_string "hello"
634 let s = Bytes.of_string "hello"
635 The first declaration is incorrect, because the string literal "hello"
638 could be shared by the compiler with other parts of the program, and
639 mutating incorrect is a bug. You must always use the second version,
640 which performs a copy and is thus correct.
641 Assuming unique ownership of strings that are not string literals, but
643 are (partly) built from string literals, is also incorrect. For exam‐
644 ple, mutating unsafe_of_string ("foo" ^ s) could mutate the shared
645 string "foo" -- assuming a rope-like representation of strings. More
646 generally, functions operating on strings will assume shared ownership,
647 they do not preserve unique ownership. It is thus incorrect to assume
648 unique ownership of the result of unsafe_of_string .
649 The only case we have reasonable confidence is safe is if the produced
651 bytes is shared -- used as an immutable byte sequence. This is possibly
652 useful for incremental migration of low-level programs that manipulate
653 immutable sequences of bytes (for example Marshal.from_bytes ) and pre‐
654 viously used the string type for this purpose.
655 val split_on_char : sep:char -> bytes -> bytes list
659 split_on_char sep s returns the list of all (possibly empty) subse‐
662 quences of s that are delimited by the sep character.
663 The function's output is specified by the following invariants:
665 -The list is not empty.
668 -Concatenating its elements using sep as a separator returns a byte se‐
670 quence equal to the input ( Bytes.concat (Bytes.make 1 sep)
671 (Bytes.split_on_char sep s) = s ).
672 -No byte sequence in the result contains the sep character.
674 Since 4.13.0
678 Iterators
683 val to_seq : t -> char Seq.t
684 Iterate on the string, in increasing index order. Modifications of the
686 string during iteration will be reflected in the sequence.
687 Since 4.07
690 val to_seqi : t -> (int * char) Seq.t
694 Iterate on the string, in increasing order, yielding indices along
696 chars
697 Since 4.07
700 val of_seq : char Seq.t -> t
704 Create a string from the generator
706 Since 4.07
709 UTF codecs and validations
714 UTF-8
715 val get_utf_8_uchar : t -> int -> Uchar.utf_decode
716 get_utf_8_uchar b i decodes an UTF-8 character at index i in b .
719 val set_utf_8_uchar : t -> int -> Uchar.t -> int
723 set_utf_8_uchar b i u UTF-8 encodes u at index i in b and returns the
726 number of bytes n that were written starting at i . If n is 0 there was
727 not enough space to encode u at i and b was left untouched. Otherwise a
728 new character can be encoded at i + n .
729 val is_valid_utf_8 : t -> bool
733 is_valid_utf_8 b is true if and only if b contains valid UTF-8 data.
736 UTF-16BE
741 val get_utf_16be_uchar : t -> int -> Uchar.utf_decode
742 get_utf_16be_uchar b i decodes an UTF-16BE character at index i in b .
745 val set_utf_16be_uchar : t -> int -> Uchar.t -> int
749 set_utf_16be_uchar b i u UTF-16BE encodes u at index i in b and returns
752 the number of bytes n that were written starting at i . If n is 0 there
753 was not enough space to encode u at i and b was left untouched. Other‐
754 wise a new character can be encoded at i + n .
755 val is_valid_utf_16be : t -> bool
759 is_valid_utf_16be b is true if and only if b contains valid UTF-16BE
762 data.
763 UTF-16LE
768 val get_utf_16le_uchar : t -> int -> Uchar.utf_decode
769 get_utf_16le_uchar b i decodes an UTF-16LE character at index i in b .
772 val set_utf_16le_uchar : t -> int -> Uchar.t -> int
776 set_utf_16le_uchar b i u UTF-16LE encodes u at index i in b and returns
779 the number of bytes n that were written starting at i . If n is 0 there
780 was not enough space to encode u at i and b was left untouched. Other‐
781 wise a new character can be encoded at i + n .
782 val is_valid_utf_16le : t -> bool
786 is_valid_utf_16le b is true if and only if b contains valid UTF-16LE
789 data.
790 Binary encoding/decoding of integers
795 The functions in this section binary encode and decode integers to and
796 from byte sequences.
797 All following functions raise Invalid_argument if the space needed at
799 index i to decode or encode the integer is not available.
800 Little-endian (resp. big-endian) encoding means that least (resp. most)
802 significant bytes are stored first. Big-endian is also known as net‐
803 work byte order. Native-endian encoding is either little-endian or
804 big-endian depending on Sys.big_endian .
805 32-bit and 64-bit integers are represented by the int32 and int64
807 types, which can be interpreted either as signed or unsigned numbers.
808 8-bit and 16-bit integers are represented by the int type, which has
810 more bits than the binary encoding. These extra bits are handled as
811 follows:
812 -Functions that decode signed (resp. unsigned) 8-bit or 16-bit integers
814 represented by int values sign-extend (resp. zero-extend) their result.
815 -Functions that encode 8-bit or 16-bit integers represented by int val‐
817 ues truncate their input to their least significant bytes.
818 val get_uint8 : bytes -> int -> int
821 get_uint8 b i is b 's unsigned 8-bit integer starting at byte index i .
824 Since 4.08
827 val get_int8 : bytes -> int -> int
831 get_int8 b i is b 's signed 8-bit integer starting at byte index i .
834 Since 4.08
837 val get_uint16_ne : bytes -> int -> int
841 get_uint16_ne b i is b 's native-endian unsigned 16-bit integer start‐
844 ing at byte index i .
845 Since 4.08
848 val get_uint16_be : bytes -> int -> int
852 get_uint16_be b i is b 's big-endian unsigned 16-bit integer starting
855 at byte index i .
856 Since 4.08
859 val get_uint16_le : bytes -> int -> int
863 get_uint16_le b i is b 's little-endian unsigned 16-bit integer start‐
866 ing at byte index i .
867 Since 4.08
870 val get_int16_ne : bytes -> int -> int
874 get_int16_ne b i is b 's native-endian signed 16-bit integer starting
877 at byte index i .
878 Since 4.08
881 val get_int16_be : bytes -> int -> int
885 get_int16_be b i is b 's big-endian signed 16-bit integer starting at
888 byte index i .
889 Since 4.08
892 val get_int16_le : bytes -> int -> int
896 get_int16_le b i is b 's little-endian signed 16-bit integer starting
899 at byte index i .
900 Since 4.08
903 val get_int32_ne : bytes -> int -> int32
907 get_int32_ne b i is b 's native-endian 32-bit integer starting at byte
910 index i .
911 Since 4.08
914 val get_int32_be : bytes -> int -> int32
918 get_int32_be b i is b 's big-endian 32-bit integer starting at byte in‐
921 dex i .
922 Since 4.08
925 val get_int32_le : bytes -> int -> int32
929 get_int32_le b i is b 's little-endian 32-bit integer starting at byte
932 index i .
933 Since 4.08
936 val get_int64_ne : bytes -> int -> int64
940 get_int64_ne b i is b 's native-endian 64-bit integer starting at byte
943 index i .
944 Since 4.08
947 val get_int64_be : bytes -> int -> int64
951 get_int64_be b i is b 's big-endian 64-bit integer starting at byte in‐
954 dex i .
955 Since 4.08
958 val get_int64_le : bytes -> int -> int64
962 get_int64_le b i is b 's little-endian 64-bit integer starting at byte
965 index i .
966 Since 4.08
969 val set_uint8 : bytes -> int -> int -> unit
973 set_uint8 b i v sets b 's unsigned 8-bit integer starting at byte index
976 i to v .
977 Since 4.08
980 val set_int8 : bytes -> int -> int -> unit
984 set_int8 b i v sets b 's signed 8-bit integer starting at byte index i
987 to v .
988 Since 4.08
991 val set_uint16_ne : bytes -> int -> int -> unit
995 set_uint16_ne b i v sets b 's native-endian unsigned 16-bit integer
998 starting at byte index i to v .
999 Since 4.08
1002 val set_uint16_be : bytes -> int -> int -> unit
1006 set_uint16_be b i v sets b 's big-endian unsigned 16-bit integer start‐
1009 ing at byte index i to v .
1010 Since 4.08
1013 val set_uint16_le : bytes -> int -> int -> unit
1017 set_uint16_le b i v sets b 's little-endian unsigned 16-bit integer
1020 starting at byte index i to v .
1021 Since 4.08
1024 val set_int16_ne : bytes -> int -> int -> unit
1028 set_int16_ne b i v sets b 's native-endian signed 16-bit integer start‐
1031 ing at byte index i to v .
1032 Since 4.08
1035 val set_int16_be : bytes -> int -> int -> unit
1039 set_int16_be b i v sets b 's big-endian signed 16-bit integer starting
1042 at byte index i to v .
1043 Since 4.08
1046 val set_int16_le : bytes -> int -> int -> unit
1050 set_int16_le b i v sets b 's little-endian signed 16-bit integer start‐
1053 ing at byte index i to v .
1054 Since 4.08
1057 val set_int32_ne : bytes -> int -> int32 -> unit
1061 set_int32_ne b i v sets b 's native-endian 32-bit integer starting at
1064 byte index i to v .
1065 Since 4.08
1068 val set_int32_be : bytes -> int -> int32 -> unit
1072 set_int32_be b i v sets b 's big-endian 32-bit integer starting at byte
1075 index i to v .
1076 Since 4.08
1079 val set_int32_le : bytes -> int -> int32 -> unit
1083 set_int32_le b i v sets b 's little-endian 32-bit integer starting at
1086 byte index i to v .
1087 Since 4.08
1090 val set_int64_ne : bytes -> int -> int64 -> unit
1094 set_int64_ne b i v sets b 's native-endian 64-bit integer starting at
1097 byte index i to v .
1098 Since 4.08
1101 val set_int64_be : bytes -> int -> int64 -> unit
1105 set_int64_be b i v sets b 's big-endian 64-bit integer starting at byte
1108 index i to v .
1109 Since 4.08
1112 val set_int64_le : bytes -> int -> int64 -> unit
1116 set_int64_le b i v sets b 's little-endian 64-bit integer starting at
1119 byte index i to v .
1120 Since 4.08
1123 Byte sequences and concurrency safety
1128 Care must be taken when concurrently accessing byte sequences from mul‐
1129 tiple domains: accessing a byte sequence will never crash a program,
1130 but unsynchronized accesses might yield surprising (non-sequen‐
1131 tially-consistent) results.
1132 Atomicity
1135 Every byte sequence operation that accesses more than one byte is not
1136 atomic. This includes iteration and scanning.
1137 For example, consider the following program:
1139 let size = 100_000_000
1140 let b = Bytes.make size ' '
1141 let update b f () =
1142 Bytes.iteri (fun i x -> Bytes.set b i (Char.chr (f (Char.code x)))) b
1143 let d1 = Domain.spawn (update b (fun x -> x + 1))
1144 let d2 = Domain.spawn (update b (fun x -> 2 * x + 1))
1145 let () = Domain.join d1; Domain.join d2
1146 the bytes sequence b may contain a non-deterministic mixture of '!' ,
1148 'A' , 'B' , and 'C' values.
1149 After executing this code, each byte of the sequence b is either '!' ,
1151 'A' , 'B' , or 'C' . If atomicity is required, then the user must im‐
1152 plement their own synchronization (for example, using Mutex.t ).
1153 Data races
1156 If two domains only access disjoint parts of a byte sequence, then the
1157 observed behaviour is the equivalent to some sequential interleaving of
1158 the operations from the two domains.
1159 A data race is said to occur when two domains access the same byte
1161 without synchronization and at least one of the accesses is a write.
1162 In the absence of data races, the observed behaviour is equivalent to
1163 some sequential interleaving of the operations from different domains.
1164 Whenever possible, data races should be avoided by using synchroniza‐
1166 tion to mediate the accesses to the elements of the sequence.
1167 Indeed, in the presence of data races, programs will not crash but the
1169 observed behaviour may not be equivalent to any sequential interleaving
1170 of operations from different domains. Nevertheless, even in the pres‐
1171 ence of data races, a read operation will return the value of some
1172 prior write to that location.
1173 Mixed-size accesses
1176 Another subtle point is that if a data race involves mixed-size writes
1177 and reads to the same location, the order in which those writes and
1178 reads are observed by domains is not specified. For instance, the fol‐
1179 lowing code write sequentially a 32-bit integer and a char to the same
1180 index
1181 let b = Bytes.make 10 '\000'
1182 let d1 = Domain.spawn (fun () -> Bytes.set_int32_ne b 0 100; b.[0] <- 'd' )
1183 In this situation, a domain that observes the write of 'd' to b. 0 is
1186 not guaranteed to also observe the write to indices 1 , 2 , or 3 .
1187OCamldoc 2023-07-20 StdLabels.Bytes(3)