fix(niri): reconnect IPC and stop per-event throttling to prevent freeze

The niri IPC worker slept 1ms per event and never reconnected. Under an
event burst the per-event cap back-pressures the socket, niri fills its
send buffer and drops the stream; read_line then returns false, the
detached thread exits and the module freezes permanently.

Remove the per-event sleep so events drain as fast as they arrive, and
wrap the socket setup and read loop in a reconnect loop that backs off
and re-establishes the stream on drop. A running_ flag lets the thread
exit cleanly on teardown.

Fixes #5117.

include/modules/niri/backend.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <atomic>
 #include <list>
 #include <mutex>
 #include <string>
@@ -18,6 +19,7 @@ class EventHandler {
 class IPC {
  public:
   IPC();
+  ~IPC();
 
   void registerForIPC(const std::string& ev, EventHandler* ev_handler);
   void unregisterForIPC(EventHandler* handler);
@@ -45,6 +47,8 @@ class IPC {
   util::JsonParser parser_;
   std::mutex callbackMutex_;
   std::list<std::pair<std::string, EventHandler*>> callbacks_;
+
+  std::atomic<bool> running_{true};
 };
 
 inline std::unique_ptr<IPC> gIPC;

src/modules/niri/backend.cpp

@@ -23,6 +23,8 @@ namespace waybar::modules::niri {
 
 IPC::IPC() { startIPC(); }
 
+IPC::~IPC() { running_ = false; }
+
 int IPC::connectToSocket() {
   const char* socket_path = getenv("NIRI_SOCKET");
 
@@ -55,11 +57,21 @@ int IPC::connectToSocket() {
 void IPC::startIPC() {
   // will start IPC and relay events to parseIPC
 
-  int socketfd = connectToSocket();
-
-  std::thread([this, socketfd]() {
+  std::thread([this]() {
     spdlog::info("Niri IPC starting");
 
+    // Reconnect loop: if the event stream drops we back off briefly and
+    // re-establish the socket instead of leaving the module frozen forever.
+    while (running_) {
+      int socketfd;
+      try {
+        socketfd = connectToSocket();
+      } catch (std::exception& e) {
+        spdlog::error("Niri IPC: failed to connect: {}", e.what());
+        std::this_thread::sleep_for(std::chrono::seconds(2));
+        continue;
+      }
+
       auto unix_istream = Gio::UnixInputStream::create(socketfd, true);
       auto unix_ostream = Gio::UnixOutputStream::create(socketfd, false);
       auto istream = Gio::DataInputStream::create(unix_istream);
@@ -67,16 +79,20 @@ void IPC::startIPC() {
 
       if (!ostream->put_string("\"EventStream\"\n") || !ostream->flush()) {
         spdlog::error("Niri IPC: failed to start event stream");
-      return;
+        std::this_thread::sleep_for(std::chrono::seconds(2));
+        continue;
       }
 
       std::string line;
       if (!istream->read_line(line) || line != R"({"Ok":"Handled"})") {
         spdlog::error("Niri IPC: failed to start event stream");
-      return;
+        std::this_thread::sleep_for(std::chrono::seconds(2));
+        continue;
       }
 
-    while (istream->read_line(line)) {
+      // Drain events as fast as they arrive; throttling here back-pressures the
+      // socket, fills niri's send buffer and makes niri drop the stream.
+      while (running_ && istream->read_line(line)) {
         spdlog::debug("Niri IPC: received {}", line);
 
         try {
@@ -86,9 +102,15 @@ void IPC::startIPC() {
         } catch (...) {
           throw;
         }
-
-      std::this_thread::sleep_for(std::chrono::milliseconds(1));
       }
+
+      if (!running_) break;
+
+      spdlog::warn("Niri IPC: event stream closed, reconnecting");
+      std::this_thread::sleep_for(std::chrono::seconds(2));
+    }
+
+    spdlog::info("Niri IPC stopping");
   }).detach();
 }
 
@@ -196,12 +218,12 @@ void IPC::parseIPC(const std::string& line) {
       for (auto& win : windows_) {
         win["is_focused"] = focused && win["id"].asUInt64() == id;
       }
-    } else if (const auto &payload = ev["WindowLayoutsChanged"]) {
-      const auto &values = payload["changes"];
-      for (const auto &changed : values) {
+    } else if (const auto& payload = ev["WindowLayoutsChanged"]) {
+      const auto& values = payload["changes"];
+      for (const auto& changed : values) {
         const auto id = changed[0].asUInt64();
-        const auto &change = changed[1];
-        for (auto &win : windows_) {
+        const auto& change = changed[1];
+        for (auto& win : windows_) {
           if (win["id"].asUInt64() == id) {
             win["layout"] = change;
             break;