From e704c261cbcbf5448b9bba1c99bcbc33fea8f556 Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Mon, 18 Aug 2025 16:35:33 -0400
Subject: [PATCH] Use a pipe instead of an eventfd

---
 src/main.cpp | 45 +++++++++++++++++++++++++--------------------
 1 file changed, 25 insertions(+), 20 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index ba11aa7..785a680 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -12,7 +12,6 @@
 #include <netdb.h>
 #include <netinet/tcp.h>
 #include <sys/epoll.h>
-#include <sys/eventfd.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <sys/un.h>
@@ -21,7 +20,7 @@
 #include <vector>
 
 std::atomic<int> activeConnections{0};
-int shutdown_eventfd = -1;
+int shutdown_pipe[2] = {-1, -1};
 
 #ifndef __has_feature
 #define __has_feature(x) 0
@@ -29,11 +28,11 @@ int shutdown_eventfd = -1;
 
 void signal_handler(int sig) {
   if (sig == SIGTERM || sig == SIGINT) {
-    if (shutdown_eventfd != -1) {
+    if (shutdown_pipe[1] != -1) {
       char val = 1;
       // write() is async-signal-safe per POSIX - safe to use in signal handler
       // Write single byte to avoid partial write complexity
-      while (write(shutdown_eventfd, &val, 1) == -1) {
+      while (write(shutdown_pipe[1], &val, 1) == -1) {
         if (errno != EINTR) {
           abort(); // graceful shutdown didn't work. Let's go ungraceful.
         }
@@ -266,10 +265,15 @@ int main(int argc, char *argv[]) {
             << config->subscription.keepalive_interval.count() << " seconds"
             << std::endl;
 
-  // Create shutdown eventfd for graceful shutdown
-  shutdown_eventfd = eventfd(0, EFD_CLOEXEC);
-  if (shutdown_eventfd == -1) {
-    perror("eventfd");
+  // Create shutdown pipe for graceful shutdown
+  if (pipe(shutdown_pipe) == -1) {
+    perror("pipe");
+    abort();
+  }
+  // Set both ends to close-on-exec
+  if (fcntl(shutdown_pipe[0], F_SETFD, FD_CLOEXEC) == -1 ||
+      fcntl(shutdown_pipe[1], F_SETFD, FD_CLOEXEC) == -1) {
+    perror("fcntl FD_CLOEXEC");
     abort();
   }
 
@@ -285,11 +289,11 @@ int main(int argc, char *argv[]) {
     perror("epoll_create");
     abort();
   }
-  // Add shutdown eventfd to network thread epoll
+  // Add shutdown pipe read end to network thread epoll
   struct epoll_event shutdown_event;
   shutdown_event.events = EPOLLIN;
-  shutdown_event.data.fd = shutdown_eventfd;
-  if (epoll_ctl(network_epollfd, EPOLL_CTL_ADD, shutdown_eventfd,
+  shutdown_event.data.fd = shutdown_pipe[0];
+  if (epoll_ctl(network_epollfd, EPOLL_CTL_ADD, shutdown_pipe[0],
                 &shutdown_event) == -1) {
     perror("epoll_ctl add shutdown event");
     abort();
@@ -323,8 +327,8 @@ int main(int argc, char *argv[]) {
 
             for (int i = 0; i < eventCount; ++i) {
               // Check for shutdown event
-              if (events[i].data.fd == shutdown_eventfd) {
-                // Don't read eventfd - all threads need to see shutdown signal
+              if (events[i].data.fd == shutdown_pipe[0]) {
+                // Don't read pipe - all threads need to see shutdown signal
                 return;
               }
 
@@ -383,10 +387,10 @@ int main(int argc, char *argv[]) {
     abort();
   }
 
-  // Add shutdown eventfd to accept epoll
-  if (epoll_ctl(accept_epollfd, EPOLL_CTL_ADD, shutdown_eventfd,
+  // Add shutdown pipe read end to accept epoll
+  if (epoll_ctl(accept_epollfd, EPOLL_CTL_ADD, shutdown_pipe[0],
                 &shutdown_event) == -1) {
-    perror("epoll_ctl shutdown eventfd");
+    perror("epoll_ctl shutdown pipe");
     abort();
   }
 
@@ -409,7 +413,7 @@ int main(int argc, char *argv[]) {
                          ("accept-" + std::to_string(acceptThreadId)).c_str());
 
       for (;;) {
-        struct epoll_event events[2]; // listen socket + shutdown eventfd
+        struct epoll_event events[2]; // listen socket + shutdown pipe
         int ready = epoll_wait(accept_epollfd, events, 2, -1 /* no timeout */);
 
         if (ready == -1) {
@@ -420,8 +424,8 @@ int main(int argc, char *argv[]) {
         }
 
         for (int i = 0; i < ready; ++i) {
-          if (events[i].data.fd == shutdown_eventfd) {
-            // Don't read eventfd - all threads need to see shutdown signal
+          if (events[i].data.fd == shutdown_pipe[0]) {
+            // Don't read pipe - all threads need to see shutdown signal
             return;
           }
 
@@ -483,7 +487,8 @@ int main(int argc, char *argv[]) {
   }
 
   // Cleanup
-  close(shutdown_eventfd);
+  close(shutdown_pipe[0]);
+  close(shutdown_pipe[1]);
   close(accept_epollfd);
   close(network_epollfd);
   close(sockfd);