mercurial/cffi/mpatchbuild.py

revlog: avoid opening and closing the file for each cloned revision

The previous code was flushing files after each new revision, slowing things
down.

For exemple, with this change, the evolve repository can run
`hg debugupgraderepo --run --optimize re-delta-parent` in about 3.4s instead of
4.5 seconds.

import cffi
import os

ffi = cffi.FFI()
mpatch_c = os.path.join(
    os.path.join(os.path.dirname(__file__), '..', 'mpatch.c')
)
with open(mpatch_c) as f:
    ffi.set_source(
        "mercurial.cffi._mpatch", f.read(), include_dirs=["mercurial"]
    )
ffi.cdef(
    """

struct mpatch_frag {
       int start, end, len;
       const char *data;
};

struct mpatch_flist {
       struct mpatch_frag *base, *head, *tail;
};

extern "Python" struct mpatch_flist* cffi_get_next_item(void*, ssize_t);

int mpatch_decode(const char *bin, ssize_t len, struct mpatch_flist** res);
ssize_t mpatch_calcsize(size_t len, struct mpatch_flist *l);
void mpatch_lfree(struct mpatch_flist *a);
static int mpatch_apply(char *buf, const char *orig, size_t len,
                        struct mpatch_flist *l);
struct mpatch_flist *mpatch_fold(void *bins,
                       struct mpatch_flist* (*get_next_item)(void*, ssize_t),
                       ssize_t start, ssize_t end);
"""
)

if __name__ == '__main__':
    ffi.compile()