Re: [PATCH] tcp_listener_stats: always eagerly close sockets

[Eric Wong <e@yhbt.net>]

Jean Boussier <jean.boussier@gmail.com> wrote:
> Hello,
> 
> Once again apologies for not submitting the patch in an usable format.
<snip>

I was actually able to run `git am' on your raw mail just fine
w/o needing an active connection.  So whatever you did worked[1]

More inline...

<snip>

> Looking at the raindrops implementation it seems to assume
> the GC will take care of regularly closing these sockets, but
> I think it’s a bit too bold of an assumption.

Your code (and some of the Ruby code shipped w/ raindrops)
should probably be reusing sockets given our API allows it.
At the top of the tcp_listener_stats function, we have:

	rb_scan_args(argc, argv, "02", &addrs, &sock);

and then:

	sock = NIL_P(sock) ? rb_funcall(cIDSock, id_new, 0)
			: rb_io_get_io(sock);

So we only create sockets one isn't passed.

> diff --git a/ext/raindrops/linux_inet_diag.c b/ext/raindrops/linux_inet_diag.c
> index 2a2360c..b3d9a51 100644
> --- a/ext/raindrops/linux_inet_diag.c
> +++ b/ext/raindrops/linux_inet_diag.c
> @@ -634,7 +634,7 @@ static VALUE tcp_listener_stats(int argc, VALUE *argv, VALUE self)
>  	switch (TYPE(addrs)) {
>  	case T_STRING:
>  		rb_hash_aset(rv, addrs, tcp_stats(&args, addrs));
> -		return rv;
> +		goto out;

OK

> @@ -643,7 +643,7 @@ static VALUE tcp_listener_stats(int argc, VALUE *argv, VALUE self)
>  			VALUE cur = rb_ary_entry(addrs, 0);
>  
>  			rb_hash_aset(rv, cur, tcp_stats(&args, cur));
> -			return rv;
> +			goto out;

OK

>  		}
>  		for (i = 0; i < len; i++) {
>  			union any_addr check;
> @@ -659,6 +659,7 @@ static VALUE tcp_listener_stats(int argc, VALUE *argv, VALUE self)
>  		gen_bytecode_all(&args.iov[2]);
>  		break;
>  	default:
> +        rb_io_close(sock);

That needs the (argc < 2) guard like below in `out:'.  We should
never close sockets passed by the user.

Indentation is also done with hard tabs for this project (and
alignment with spaces, roughly git.git and Linux kernel style)[2].
I'll push out the patch below if it looks OK to you.

>  		rb_raise(rb_eArgError,
>  		         "addr must be an array of strings, a string, or nil");
>  	}
> @@ -671,6 +672,7 @@ static VALUE tcp_listener_stats(int argc, VALUE *argv, VALUE self)
>  	if (RHASH_SIZE(rv) > 1)
>  		rb_hash_foreach(rv, drop_placeholders, Qfalse);
>  
> +out:

OK.

>  	/* let GC deal with corner cases */
>  	if (argc < 2) rb_io_close(sock);
>  	return rv;

That 'if (argc < 2)' is important for the exception above.

This is what I'll push out:
-----8<-----
From: Jean Boussier <jean.boussier@gmail.com>
Subject: [PATCH] tcp_listener_stats: always eagerly close sockets

I just debugged an issue with our system, I was witnessing the
number of file descriptor in our process grow at an alarming rate
which I mapped to our use of raindrops to report utilisation.

For various reasons we don’t call raindrops from a Rack middleware
but have one process that monitor the socket continuously, and
share that data with the workers.

Since we call tcp_listener_stats every seconds in a process
that doesn't do much else, GC very rarely triggers if at all
 which cause `InetDiagSocket` instances to accumulate very
quickly.

Each of those instances holds a file descriptor.

Looking at the raindrops implementation it seems to assume
the GC will take care of regularly closing these sockets, but
I think it’s a bit too bold of an assumption.

[ew: don't close user-passed sockets on exception]

Acked-by: Eric Wong <e@80x24.org>
---
Range-diff:
1:  6a93833 ! 1:  9b9909b tcp_listener_stats: always eagerly close sockets
    @@ Commit message
         the GC will take care of regularly closing these sockets, but
         I think it’s a bit too bold of an assumption.
     
    +    [ew: don't close user-passed sockets on exception]
    +
    +    Acked-by: Eric Wong <e@80x24.org>
    +
      ## ext/raindrops/linux_inet_diag.c ##
     @@ ext/raindrops/linux_inet_diag.c: static VALUE tcp_listener_stats(int argc, VALUE *argv, VALUE self)
      	switch (TYPE(addrs)) {
    @@ ext/raindrops/linux_inet_diag.c: static VALUE tcp_listener_stats(int argc, VALUE
      		gen_bytecode_all(&args.iov[2]);
      		break;
      	default:
    -+        rb_io_close(sock);
    ++		if (argc < 2) rb_io_close(sock);
      		rb_raise(rb_eArgError,
      		         "addr must be an array of strings, a string, or nil");
      	}

 ext/raindrops/linux_inet_diag.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/ext/raindrops/linux_inet_diag.c b/ext/raindrops/linux_inet_diag.c
index 2d4f503..e4050cb 100644
--- a/ext/raindrops/linux_inet_diag.c
+++ b/ext/raindrops/linux_inet_diag.c
@@ -636,7 +636,7 @@ static VALUE tcp_listener_stats(int argc, VALUE *argv, VALUE self)
 	switch (TYPE(addrs)) {
 	case T_STRING:
 		rb_hash_aset(rv, addrs, tcp_stats(&args, addrs));
-		return rv;
+		goto out;
 	case T_ARRAY: {
 		long i;
 		long len = RARRAY_LEN(addrs);
@@ -645,7 +645,7 @@ static VALUE tcp_listener_stats(int argc, VALUE *argv, VALUE self)
 			VALUE cur = rb_ary_entry(addrs, 0);
 
 			rb_hash_aset(rv, cur, tcp_stats(&args, cur));
-			return rv;
+			goto out;
 		}
 		for (i = 0; i < len; i++) {
 			union any_addr check;
@@ -661,6 +661,7 @@ static VALUE tcp_listener_stats(int argc, VALUE *argv, VALUE self)
 		gen_bytecode_all(&args.iov[2]);
 		break;
 	default:
+		if (argc < 2) rb_io_close(sock);
 		rb_raise(rb_eArgError,
 		         "addr must be an array of strings, a string, or nil");
 	}
@@ -673,6 +674,7 @@ static VALUE tcp_listener_stats(int argc, VALUE *argv, VALUE self)
 	if (RHASH_SIZE(rv) > 1)
 		rb_hash_foreach(rv, drop_placeholders, Qfalse);
 
+out:
 	/* let GC deal with corner cases */
 	rb_str_resize(buf, 0);
 	if (argc < 2) rb_io_close(sock);

[1] Fwiw, the mail submission port is open on yhbt.net and you
    can use `git send-email' with it:
    git send-email \
	--smtp-domain=yhbt.net \
	--smtp-debug=1 \
	--smtp-encryption=tls \
	--smtp-server-port=587 \
	--smtp-server=yhbt.net \
	--to raindrops-public@yhbt.net \
	--suppress-cc=all /path/to/patches

     If you prefer pull requests, format messages with the
     "git request-pull" command so they're easy to search for[3].
     Sorry, but using a proprietary+centralized hosting service
     owned by a convicted monopolist puts me in a bad mood,
     especially when I'm to blame for their success given my
     involvement in git.git.  repo.or.cz and Sourcehut are
     100% Free Software if you don't feel like self-hosting.

[2] yes, tabs were roughly ~16% faster for `git grep'
    https://lore.kerne.org/git/20071018024553.GA5186@coredump.intra.peff.net/

[3] There are automated bots and search queries that can search
    for these in mail archives.  While none are currently in use
    for this project, https://yhbt.net/raindrops.git will
    probably feature it in the nearish future.