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real-time stats for preforking Rack servers
   commit e2dfea8b2c74d94b66efc00c2ccab3df7af750a5 (patch)
   parent d08f1f3 aggregate/last_data_recv: support Socket#accept{,_nonblock}
     tree 3bf30114684d7d33661e1eb761b21ae11286b7d3
   author Jean Boussier <jean.boussier@gmail.com>  2023-09-26 21:40:00 +0000
committer Eric Wong <bofh@yhbt.net>                2023-12-29 17:46:58 +0000

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

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>
 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)
+		if (argc < 2) rb_io_close(sock);
 		         "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);
 	/* let GC deal with corner cases */
 	rb_str_resize(buf, 0);
 	if (argc < 2) rb_io_close(sock);

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