Excerpts from Gregory Szorc's message of 2016-12-17 16:40:12 -0800: > It's probably not worth worrying about just yet, but with Linux PID > namespaces, multiple processes may think they have the same PID, even if that > PID maps to different values inside the kernel. > > Mozilla has encountered problems with multiple hg processes running in > separate containers and PID namespaces acquiring the same lock from a shared > filesystem simultaneously because multiple hg processes share the same PID > and hostname in different "containers."
Pid namespace breaks mercurial lock, which is a symlink with the content "host:pid". Note that chg lock is not related to correctness. Without lock, chg also behaves correctly, with the downside: 1. More redirections. 2. Spawn servers with a same config hash in parallel unnecessarily. This series resolves 1. But that's just "nice-to-have". Even if we just drop locks today, chg won't have correctness issues. > > > On Dec 16, 2016, at 17:49, Jun Wu <qu...@fb.com> wrote: > > > > # HG changeset patch > > # User Jun Wu <qu...@fb.com> > > # Date 1481938472 0 > > # Sat Dec 17 01:34:32 2016 +0000 > > # Node ID 6c9ce8399350d8287599cd802b91adf73db08759 > > # Parent 69d25b06467d65bf6d1e85d34d8fc57ec321b51d > > # Available At https://bitbucket.org/quark-zju/hg-draft > > # hg pull https://bitbucket.org/quark-zju/hg-draft -r > > 6c9ce8399350 > > chg: start server at a unique address > > > > See the previous patch for motivation. Previously, the server is started at > > a globally shared address, which requires a lock. This patch appends pid to > > the address so it becomes unique. > > > > diff --git a/contrib/chg/chg.c b/contrib/chg/chg.c > > --- a/contrib/chg/chg.c > > +++ b/contrib/chg/chg.c > > @@ -32,4 +32,5 @@ > > struct cmdserveropts { > > char sockname[UNIX_PATH_MAX]; > > + char initsockname[UNIX_PATH_MAX]; > > char redirectsockname[UNIX_PATH_MAX]; > > char lockfile[UNIX_PATH_MAX]; > > @@ -164,4 +165,8 @@ static void setcmdserveropts(struct cmds > > if (r < 0 || (size_t)r >= sizeof(opts->lockfile)) > > abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r); > > + r = snprintf(opts->initsockname, sizeof(opts->initsockname), > > + "%s.%u", opts->sockname, (unsigned)getpid()); > > + if (r < 0 || (size_t)r >= sizeof(opts->initsockname)) > > + abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r); > > } > > > > @@ -224,5 +229,5 @@ static void execcmdserver(const struct c > > "serve", > > "--cmdserver", "chgunix", > > - "--address", opts->sockname, > > + "--address", opts->initsockname, > > "--daemon-postexec", "chdir:/", > > }; > > @@ -248,5 +253,5 @@ static hgclient_t *retryconnectcmdserver > > int pst = 0; > > > > - debugmsg("try connect to %s repeatedly", opts->sockname); > > + debugmsg("try connect to %s repeatedly", opts->initsockname); > > > > unsigned int timeoutsec = 60; /* default: 60 seconds */ > > @@ -256,7 +261,13 @@ static hgclient_t *retryconnectcmdserver > > > > for (unsigned int i = 0; !timeoutsec || i < timeoutsec * 100; i++) { > > - hgclient_t *hgc = hgc_open(opts->sockname); > > - if (hgc) > > + hgclient_t *hgc = hgc_open(opts->initsockname); > > + if (hgc) { > > + debugmsg("rename %s to %s", opts->initsockname, > > + opts->sockname); > > + int r = rename(opts->initsockname, opts->sockname); > > + if (r != 0) > > + abortmsgerrno("cannot rename"); > > return hgc; > > + } > > > > if (pid > 0) { > > @@ -270,5 +281,5 @@ static hgclient_t *retryconnectcmdserver > > } > > > > - abortmsg("timed out waiting for cmdserver %s", opts->sockname); > > + abortmsg("timed out waiting for cmdserver %s", opts->initsockname); > > return NULL; > > > > @@ -313,5 +324,5 @@ static hgclient_t *connectcmdserver(stru > > unlink(opts->sockname); > > > > - debugmsg("start cmdserver at %s", opts->sockname); > > + debugmsg("start cmdserver at %s", opts->initsockname); > > > > pid_t pid = fork(); > > https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel _______________________________________________ Mercurial-devel mailing list Mercurial-devel@mercurial-scm.org https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel
