On 09/13/2017 07:15 PM, Michael Haggerty wrote:
> [...]
> * `mmap()` the whole file rather than `read()`ing it.
> [...]
Apparently this doesn't work on Windows, because the `snapshot` is
keeping the `packed-refs` file open too long, so the new file can't be
renamed on top of it.
I didn't realize that this is even allowed, but TIL that you can close a
file while keeping it mmapped. Does that technique work on Windows? If
so, I'll change v2 to do it as sketched below.
Michael
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 8235ac8506..95c1cd2a27 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -35,11 +35,8 @@ struct snapshot {
*/
struct packed_ref_store *refs;
- /*
- * The file descriptor of the `packed-refs` file (open in
- * read-only mode), or -1 if it is not open.
- */
- int fd;
+ /* Is the `packed-refs` file currently mmapped? */
+ int mmapped;
/*
* The contents of the `packed-refs` file. If the file was
@@ -135,12 +132,11 @@ static void acquire_snapshot(struct snapshot
*snapshot)
*/
static void clear_snapshot_buffer(struct snapshot *snapshot)
{
- if (snapshot->fd >= 0) {
+ if (snapshot->mmapped) {
if (munmap(snapshot->buf, snapshot->eof - snapshot->buf))
die_errno("error ummapping packed-refs file %s",
snapshot->refs->path);
- close(snapshot->fd);
- snapshot->fd = -1;
+ snapshot->mmapped = 0;
} else {
free(snapshot->buf);
}
@@ -525,6 +521,7 @@ static const char *find_reference_location(struct
snapshot *snapshot,
static struct snapshot *create_snapshot(struct packed_ref_store *refs)
{
struct snapshot *snapshot = xcalloc(1, sizeof(*snapshot));
+ int fd;
struct stat st;
size_t size;
int sorted = 0;
@@ -533,8 +530,8 @@ static struct snapshot *create_snapshot(struct
packed_ref_store *refs)
acquire_snapshot(snapshot);
snapshot->peeled = PEELED_NONE;
- snapshot->fd = open(refs->path, O_RDONLY);
- if (snapshot->fd < 0) {
+ fd = open(refs->path, O_RDONLY);
+ if (fd < 0) {
if (errno == ENOENT) {
/*
* This is OK; it just means that no
@@ -549,15 +546,16 @@ static struct snapshot *create_snapshot(struct
packed_ref_store *refs)
}
}
- stat_validity_update(&snapshot->validity, snapshot->fd);
+ stat_validity_update(&snapshot->validity, fd);
- if (fstat(snapshot->fd, &st) < 0)
+ if (fstat(fd, &st) < 0)
die_errno("couldn't stat %s", refs->path);
size = xsize_t(st.st_size);
- snapshot->buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE,
- snapshot->fd, 0);
+ snapshot->buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
snapshot->eof = snapshot->buf + size;
+ snapshot->mmapped = 1;
+ close(fd);
/* If the file has a header line, process it: */
if (snapshot->buf < snapshot->eof && *snapshot->buf == '#') {
