On Tue, Apr 1, 2014 at 11:58 AM, Michael Haggerty <mhagger@xxxxxxxxxxxx> wrote:
> Add a new option flag, LOCK_SEPARATE_STAGING_FILE, that can be passed
> to hold_lock_file_for_update() or hold_lock_file_for_append() to use a
> staging file that is independent of the lock file.
>
> Add a new function activate_staging_file() that activates the contents
> that have been written to the staging file without releasing the lock.
>
> This functionality can be used to ensure that changes to two files are
> seen by other processes in one order even if correctness requires the
> locks to be released in another order.
>
> Signed-off-by: Michael Haggerty <mhagger@xxxxxxxxxxxx>
> ---
> diff --git a/lockfile.c b/lockfile.c
> index c06e134..336b914 100644
> --- a/lockfile.c
> +++ b/lockfile.c
> @@ -271,19 +325,54 @@ int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
> return fd;
> }
>
> -int close_lock_file(struct lock_file *lk)
> +static int close_staging_file(struct lock_file *lk)
> {
> int fd = lk->fd;
> +
> lk->fd = -1;
> return close(fd);
> }
>
> -int commit_lock_file(struct lock_file *lk)
> +int close_lock_file(struct lock_file *lk)
> {
> - if (lk->fd >= 0 && close_lock_file(lk))
> - return -1;
> - if (rename(lk->staging_filename.buf, lk->filename.buf))
> + assert(!(lk->flags & LOCK_FLAGS_SEPARATE_STAGING_FILE));
> + return close_staging_file(lk);
> +}
> +
> +int activate_staging_file(struct lock_file *lk)
> +{
> + int err;
> +
> + assert(lk->flags & LOCK_FLAGS_SEPARATE_STAGING_FILE);
> + assert(lk->fd >= 0);
> + assert(lk->staging_filename.len);
> +
> + if (close_staging_file(lk))
> return -1;
> +
> + err = rename(lk->staging_filename.buf, lk->filename.buf);
> + strbuf_setlen(&lk->staging_filename, 0);
strbuf_reset()?
> +
> + return err;
> +}
> +
> +int commit_lock_file(struct lock_file *lk)
> +{
> + if (lk->flags & LOCK_FLAGS_SEPARATE_STAGING_FILE) {
> + if (lk->staging_filename.len) {
> + assert(lk->fd >= 0);
> + if (activate_staging_file(lk))
> + return -1;
> + }
> + strbuf_addbuf(&lk->staging_filename, &lk->filename);
> + strbuf_addstr(&lk->staging_filename, ".lock");
> + unlink_or_warn(lk->staging_filename.buf);
> + } else {
> + if (lk->fd >= 0 && close_lock_file(lk))
> + return -1;
> + if (rename(lk->staging_filename.buf, lk->filename.buf))
> + return -1;
> + }
> reset_lock_file(lk);
> return 0;
> }
> @@ -318,10 +407,21 @@ int commit_locked_index(struct lock_file *lk)
>
> void rollback_lock_file(struct lock_file *lk)
> {
> - if (lk->filename.len) {
> - if (lk->fd >= 0)
> - close_lock_file(lk);
> - unlink_or_warn(lk->staging_filename.buf);
> - reset_lock_file(lk);
> + if (!lk->filename.len)
> + return;
> +
> + if (lk->fd >= 0)
> + close_staging_file(lk);
> +
> + if (lk->flags & LOCK_FLAGS_SEPARATE_STAGING_FILE) {
> + if (lk->staging_filename.len) {
> + unlink_or_warn(lk->staging_filename.buf);
> + strbuf_setlen(&lk->staging_filename, 0);
strbuf_reset()?
> + }
> + strbuf_addbuf(&lk->staging_filename, &lk->filename);
> + strbuf_addstr(&lk->staging_filename, ".lock");
> }
> +
> + unlink_or_warn(lk->staging_filename.buf);
> + reset_lock_file(lk);
> }
> --
> 1.9.0
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