On Fri, 28 Sep 2018 15:31:09 +0200, Georges Racinet wrote:
> # HG changeset patch
> # User Georges Racinet <graci...@anybox.fr>
> # Date 1538059896 -7200
> # Thu Sep 27 16:51:36 2018 +0200
> # Node ID de88c09512565ed1c12e2ff9159e06ed8d762d15
> # Parent d8c9571755a64e1fc3429587dfd3949b9862eceb
> # EXP-Topic rustancestors-rfc
> rust: iterator bindings to C code
>
> In this changeset, still made of Rust code only,
> we expose the Rust iterator for instantiation and
> consumption from C code.
>
> The idea is that both the index and index_get_parents()
> will be passed from the C extension, hence avoiding a hard
> link dependency to parsers.so, so that the crate can
> still be built and tested independently.
Just a note. That means parents() can't take hidden revisions into account.
We might have to filter out hidden revisions from the initial set.
Another idea is to scan the revlog index in pure Rust. That's fairly easy
since each revlog entry is fixed sized unless data is inlined. I'm sure
there are several revlog parsers written by Mecurial folks to learn Rust.
I have one. :)
> +use std::boxed::Box;
Nit: it's included in prelude.
> +type IndexPtr = *mut c_void;
> +type IndexParentsFn = extern "C" fn(index: IndexPtr,
> + rev: ssize_t,
> + ps: *mut [c_int; 2],
> + max_rev: c_int)
> + -> c_int;
...
> +impl Graph for Index {
> + /// wrap a call to the C extern parents function
> + fn parents(&self, rev: i32) -> (i32, i32) {
> + let mut res: [c_int; 2] = [0; 2];
> + // surprisingly the call below is not unsafe, whereas calling the
> + // same extern function directly (not through a pointer) would.
> + // Maybe that depends on rustc version, though.
> + let code = (self.parents)(
Perhaps, the IndexParentsFn type has to be labeled as "unsafe fn".
> +/// Wrapping of AncestorsIterator<CIndex> constructor, for C callers.
> +///
> +/// Besides `initrevs`, `stoprev` and `inclusive`, that are converted
> +/// we receive the index and the parents function as pointers
> +#[no_mangle]
> +pub extern "C" fn rustlazyancestors_init(
> + index: IndexPtr,
> + parents: IndexParentsFn,
> + initrevslen: usize,
> + initrevs: *mut i64,
> + stoprev: i64,
> + inclusive: i64,
> +) -> *mut AncestorsIterator<Index> {
> + let v: Vec<i64> =
> + unsafe { Vec::from_raw_parts(initrevs, initrevslen, initrevslen) };
It's probably wrong to construct a Vec from a memory not allocated in Rust.
Rust uses specialized malloc() variants. IIRC, the default is jemalloc and
Vec has some other optimizations.
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