Add Ctypes_memory.keep_alive function
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Expose this function as Ctypes.keep_alive, and add documentation to the Ctypes.mli for it. In addition, remove the old `use_value` completely: from ctypes_roots.c, from cstubs_memory_stubs.ml. Add `Cstubs_internal.keep_alive` and change code-gen to use this instead of old `use_value`.
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Related to: #571 |
yallop
requested changes
Jul 29, 2024
| @@ -198,6 +198,24 @@ val allocate_n : ?finalise:('a ptr -> unit) -> 'a typ -> count:int -> 'a ptr | |||
| memory is allocated with libc's [calloc] and is guaranteed to be | |||
| zero-filled. *) | |||
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| val keep_alive : 'a -> unit | |||
| (** Inserting [keep_alive x;] in a sequence of expressions ensures that | |||
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Suggested change
| (** Inserting [keep_alive x;] in a sequence of expressions ensures that | |
| (** Inserting [keep_alive x] in a sequence of expressions ensures that |
| @@ -198,6 +198,24 @@ val allocate_n : ?finalise:('a ptr -> unit) -> 'a typ -> count:int -> 'a ptr | |||
| memory is allocated with libc's [calloc] and is guaranteed to be | |||
| zero-filled. *) | |||
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| val keep_alive : 'a -> unit | |||
| (** Inserting [keep_alive x;] in a sequence of expressions ensures that | |||
| the garbage collector will not collect [x] until after that [keep_alive] | |||
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| the garbage collector will not collect [x] until after that [keep_alive] | |
| the garbage collector will not collect [x] until [keep_alive] |
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| let strchr = Foreign.foreign "strchr" (ptr char @-> char @-> returning (ptr char)) in | ||
| let p = CArray.of_string "abc" in | ||
| let q = strchr (CArray.start p) 'a' in | ||
| let () = Gc.compact () in | ||
| let () = Printf.printf "%c\n" !@q in | ||
| keep_alive p; | ||
| ]} | ||
| Without the [keep_alive p] at the bottom, [p] could be collected during the | ||
| [Gc.compact ()] call, which would make [q] an invalid pointer into the | ||
| now-collected [p], leading to undefined behavior. *) |
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This is a nice example, but I think it would be even stronger without the call to Gc.compact, because most programs don't call Gc functions.
| let q = strchr (CArray.start p) 'a' in | ||
| let () = Gc.compact () in | ||
| let () = Printf.printf "%c\n" !@q in | ||
| keep_alive p; |
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| keep_alive p; | |
| keep_alive p |
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| (* To avoid a dependence on Ctypes_memory, we redefine keep_alive here. *) | ||
| let keep_alive x = ignore (Sys.opaque_identity x) in | ||
| Gc.finalise (fun _ -> keep_alive src) ba; ba |
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| (* To avoid a dependence on Ctypes_memory, we redefine keep_alive here. *) | |
| let keep_alive x = ignore (Sys.opaque_identity x) in | |
| Gc.finalise (fun _ -> keep_alive src) ba; ba | |
| Gc.finalise (fun _ -> ignore (Sys.opaque_identity src)) ba; ba |
| @@ -1,6 +1,6 @@ | |||
| (lang dune 2.9) | |||
| (name ctypes) | |||
| (version 0.22.0) | |||
| (version 0.23.0) | |||
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There's no need to change the version
| let () = Printf.printf "%c\n" !@q in | ||
| keep_alive p; | ||
| ]} | ||
| Without the [keep_alive p] at the bottom, [p] could be collected during the |
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Suggested change
| Without the [keep_alive p] at the bottom, [p] could be collected during the | |
| Without [keep_alive p], [p] could be collected during the |
| keep_alive p; | ||
| ]} | ||
| Without the [keep_alive p] at the bottom, [p] could be collected during the | ||
| [Gc.compact ()] call, which would make [q] an invalid pointer into the |
There was a problem hiding this comment.
Suggested change
| [Gc.compact ()] call, which would make [q] an invalid pointer into the | |
| [Gc.compact ()] call, making [q] an invalid pointer into the |
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Expose this function as Ctypes.keep_alive, and add documentation to the Ctypes.mli for it. In addition, remove the old
use_valuecompletely: from ctypes_roots.c, from cstubs_memory_stubs.ml.Add
Cstubs_internal.keep_aliveand change code-gen to use this instead of olduse_value.