From 6ba9302b91f366fb401e0300dd231f7c63208038 Mon Sep 17 00:00:00 2001
From: Anton Kirilov <antonvkirilov@gmail.com>
Date: Sat, 11 Jan 2025 21:20:18 +0000
Subject: [PATCH] H2O: Track connection load across the worker threads

---
 frameworks/C/h2o/src/event_loop.c | 29 +++++++++++++++++++++++++++++
 frameworks/C/h2o/src/event_loop.h |  5 +++++
 2 files changed, 34 insertions(+)

diff --git a/frameworks/C/h2o/src/event_loop.c b/frameworks/C/h2o/src/event_loop.c
index d5e138348de..5e49f246d60 100644
--- a/frameworks/C/h2o/src/event_loop.c
+++ b/frameworks/C/h2o/src/event_loop.c
@@ -32,13 +32,16 @@
 #include <netinet/tcp.h>
 #include <openssl/ssl.h>
 #include <sys/socket.h>
+#include <sys/syscall.h>
 #include <sys/types.h>
 
 #include "error.h"
 #include "event_loop.h"
 #include "global_data.h"
 #include "thread.h"
+#include "utility.h"
 
+#define CONN_NUM_SAMPLE_PERIOD 2500
 #define DEFAULT_TCP_FASTOPEN_QUEUE_LEN 4096
 
 static void accept_connection(h2o_socket_t *listener, const char *err);
@@ -72,6 +75,7 @@ static void accept_connection(h2o_socket_t *listener, const char *err)
 				if (!sock)
 					break;
 
+				ctx->event_loop.accepted_conn_num++;
 				ctx->event_loop.conn_num++;
 				sock->on_close.cb = on_close_connection;
 				sock->on_close.data = &ctx->event_loop.conn_num;
@@ -277,11 +281,36 @@ static void start_accept_polling(const config_t *config,
 
 void event_loop(struct thread_context_t *ctx)
 {
+	uint64_t last_sample = 0;
+
 	while (!ctx->shutdown || ctx->event_loop.conn_num) {
 		h2o_evloop_run(ctx->event_loop.h2o_ctx.loop, INT32_MAX);
 		process_messages(&ctx->global_thread_data->h2o_receiver,
 		                 &ctx->event_loop.local_messages);
+
+		const uint64_t now = h2o_now(ctx->event_loop.h2o_ctx.loop);
+
+		if (now - last_sample > CONN_NUM_SAMPLE_PERIOD || last_sample > now) {
+			const size_t i = ctx->event_loop.conn_num_sample_idx;
+
+			ctx->event_loop.conn_num_sample[i] = ctx->event_loop.conn_num;
+			ctx->event_loop.conn_num_sample_idx =
+				(i + 1) % ARRAY_SIZE(ctx->event_loop.conn_num_sample);
+			last_sample = now;
+		}
 	}
+
+	flockfile(stdout);
+	printf("Thread %ld statistics:\nAccepted connections: %zu\nConnection number samples: %zu",
+	       syscall(SYS_gettid),
+	       ctx->event_loop.accepted_conn_num,
+	       *ctx->event_loop.conn_num_sample);
+
+	for (size_t i = 1; i < ARRAY_SIZE(ctx->event_loop.conn_num_sample); i++)
+		printf(",%zu", ctx->event_loop.conn_num_sample[i]);
+
+	putc_unlocked('\n', stdout);
+	funlockfile(stdout);
 }
 
 void free_event_loop(event_loop_t *event_loop, h2o_multithread_receiver_t *h2o_receiver)
diff --git a/frameworks/C/h2o/src/event_loop.h b/frameworks/C/h2o/src/event_loop.h
index cff091154c7..41a1f3b920f 100644
--- a/frameworks/C/h2o/src/event_loop.h
+++ b/frameworks/C/h2o/src/event_loop.h
@@ -27,6 +27,8 @@
 
 #include "global_data.h"
 
+#define CONN_NUM_SAMPLES 512
+
 typedef enum {
 	SHUTDOWN,
 	TASK
@@ -41,6 +43,9 @@ typedef struct {
 	h2o_accept_ctx_t h2o_accept_ctx;
 	h2o_context_t h2o_ctx;
 	h2o_linklist_t local_messages;
+	size_t accepted_conn_num;
+	size_t conn_num_sample[CONN_NUM_SAMPLES];
+	size_t conn_num_sample_idx;
 } event_loop_t;
 
 typedef struct {