From 2777bf4046487a40444b5fb101857700181fac6b Mon Sep 17 00:00:00 2001
From: Tyler Karaszewski <tyler@expensify.com>
Date: Tue, 7 Apr 2026 16:47:36 -0700
Subject: [PATCH 1/3] Check liveness before returning socket

---
 libstuff/SSocketPool.cpp | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/libstuff/SSocketPool.cpp b/libstuff/SSocketPool.cpp
index 1fae5ebfc..4518db4a9 100644
--- a/libstuff/SSocketPool.cpp
+++ b/libstuff/SSocketPool.cpp
@@ -51,16 +51,26 @@ void SSocketPool::_timeoutThreadFunc()
 unique_ptr<STCPManager::Socket> SSocketPool::getSocket()
 {
     {
-        // If there's an existing socket, return it.
         lock_guard<mutex> lock(_poolMutex);
-        if (_sockets.size()) {
-            pair<chrono::steady_clock::time_point, unique_ptr<STCPManager::Socket>> s = move(_sockets.front());
+        while (_sockets.size()) {
+            auto s = move(_sockets.front());
             _sockets.pop_front();
-            return move(s.second);
+
+            // Verify the socket is still alive before returning it.
+            if (s.second->state.load() == STCPManager::Socket::CONNECTED) {
+                struct pollfd pfd = {s.second->s, POLLIN | POLLOUT, 0};
+                int ret = poll(&pfd, 1, 0);
+                if (ret >= 0 && !(pfd.revents & (POLLERR | POLLHUP | POLLNVAL))) {
+                    return move(s.second);
+                }
+            }
+
+            // Socket is dead, discard it (destructor closes fd).
+            SINFO("[SOCKET] Discarding stale socket from pool for host '" << host << "'.");
         }
     }
 
-    // If we get here, we need to create a socket to return. No need to hold the lock, so it goes out of scope.
+    // No live pooled socket available, create a new one. No need to hold the lock, so it goes out of scope.
     try {
         // TODO: Allow S_socket to take a parsed address instead of redoing all the parsing each time.
         return unique_ptr<STCPManager::Socket>(new STCPManager::Socket(host));

From 191a544bb862b50a87f782ada96073a6a1ced6e8 Mon Sep 17 00:00:00 2001
From: Tyler Karaszewski <tyler@expensify.com>
Date: Tue, 7 Apr 2026 16:48:34 -0700
Subject: [PATCH 2/3] Only hold lock around popping socket

---
 libstuff/SSocketPool.cpp | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/libstuff/SSocketPool.cpp b/libstuff/SSocketPool.cpp
index 4518db4a9..3e385d7b7 100644
--- a/libstuff/SSocketPool.cpp
+++ b/libstuff/SSocketPool.cpp
@@ -50,24 +50,28 @@ void SSocketPool::_timeoutThreadFunc()
 
 unique_ptr<STCPManager::Socket> SSocketPool::getSocket()
 {
-    {
-        lock_guard<mutex> lock(_poolMutex);
-        while (_sockets.size()) {
-            auto s = move(_sockets.front());
+    while (true) {
+        unique_ptr<STCPManager::Socket> socket;
+        {
+            lock_guard<mutex> lock(_poolMutex);
+            if (_sockets.empty()) {
+                break;
+            }
+            socket = move(_sockets.front().second);
             _sockets.pop_front();
+        }
 
-            // Verify the socket is still alive before returning it.
-            if (s.second->state.load() == STCPManager::Socket::CONNECTED) {
-                struct pollfd pfd = {s.second->s, POLLIN | POLLOUT, 0};
-                int ret = poll(&pfd, 1, 0);
-                if (ret >= 0 && !(pfd.revents & (POLLERR | POLLHUP | POLLNVAL))) {
-                    return move(s.second);
-                }
+        // Verify the socket is still alive before returning it.
+        if (socket->state.load() == STCPManager::Socket::CONNECTED) {
+            struct pollfd pfd = {socket->s, POLLIN | POLLOUT, 0};
+            int ret = poll(&pfd, 1, 0);
+            if (ret >= 0 && !(pfd.revents & (POLLERR | POLLHUP | POLLNVAL))) {
+                return socket;
             }
-
-            // Socket is dead, discard it (destructor closes fd).
-            SINFO("[SOCKET] Discarding stale socket from pool for host '" << host << "'.");
         }
+
+        // Socket is dead, discard it (destructor closes fd).
+        SINFO("[SOCKET] Discarding stale socket from pool for host '" << host << "'.");
     }
 
     // No live pooled socket available, create a new one. No need to hold the lock, so it goes out of scope.

From 81ca7fc939162c9a6ea893493de8402b6944c897 Mon Sep 17 00:00:00 2001
From: Tyler Karaszewski <tyler@expensify.com>
Date: Tue, 7 Apr 2026 16:59:11 -0700
Subject: [PATCH 3/3] Dont' skip verification on connecting sockets

---
 libstuff/SSocketPool.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstuff/SSocketPool.cpp b/libstuff/SSocketPool.cpp
index 3e385d7b7..114a2ae2c 100644
--- a/libstuff/SSocketPool.cpp
+++ b/libstuff/SSocketPool.cpp
@@ -62,7 +62,7 @@ unique_ptr<STCPManager::Socket> SSocketPool::getSocket()
         }
 
         // Verify the socket is still alive before returning it.
-        if (socket->state.load() == STCPManager::Socket::CONNECTED) {
+        if (socket->state.load() != STCPManager::Socket::CLOSED) {
             struct pollfd pfd = {socket->s, POLLIN | POLLOUT, 0};
             int ret = poll(&pfd, 1, 0);
             if (ret >= 0 && !(pfd.revents & (POLLERR | POLLHUP | POLLNVAL))) {