Implement the Wine host process watchdog

This will shut down a bridge's sockets when the connected native host
process exits, to prevent dangling Wine processes.

src/wine-host/bridges/common.cpp

@@ -16,13 +16,17 @@
 
 #include "common.h"
 
+#include <iostream>
+
 #include "../editor.h"
 
 HostBridge::HostBridge(MainContext& main_context,
-                       boost::filesystem::path plugin_path)
+                       boost::filesystem::path plugin_path,
+                       pid_t parent_pid)
     : plugin_path(plugin_path),
       main_context(main_context),
       generic_logger(Logger::create_wine_stderr()),
+      parent_pid(parent_pid),
       watchdog_guard(main_context.register_watchdog(*this)) {}
 
 void HostBridge::handle_win32_events() {
@@ -37,5 +41,17 @@ void HostBridge::handle_win32_events() {
 }
 
 void HostBridge::shutdown_if_dangling() {
-    // TODO: Implement
+    // If the parent process has exited and this plugin bridge instance is
+    // outliving the process it's supposed to be connected to (because in some
+    // situations sockets won't get closed when this happens so we'd hang on
+    // `recv()`), then we'll close the sockets here so that the plugin bridge
+    // exits gracefully. This will be periodically called from `MainContext`'s
+    // watchdog thread.
+    if (!pid_running(parent_pid)) {
+        std::cerr << "WARNING: The native plugin host seems to have died."
+                  << std::endl;
+        std::cerr << "         This bridge will shut down now." << std::endl;
+
+        close_sockets();
+    }
 }

src/wine-host/bridges/common.h

@@ -32,7 +32,9 @@
  */
 class HostBridge {
    protected:
-    HostBridge(MainContext& main_context, boost::filesystem::path plugin_path);
+    HostBridge(MainContext& main_context,
+               boost::filesystem::path plugin_path,
+               pid_t parent_pid);
 
    public:
     virtual ~HostBridge(){};
@@ -127,6 +129,15 @@ class HostBridge {
     Logger generic_logger;
 
    private:
+    /**
+     * The process ID of the native plugin host we are bridging for. This should
+     * be the parent, but it might not be because of Wine's startup script,
+     * `WINELOADER`s and Wine's `start.exe` behaviour. We'll periodically check
+     * if this process is still alive, and close the sockets if it is not to
+     * prevent dangling processes.
+     */
+    const pid_t parent_pid;
+
     /**
      * A guard that, while in scope, will cause `shutdown_if_dangling()` to
      * periodically be called.

src/wine-host/bridges/group.cpp

@@ -217,13 +217,13 @@ void GroupBridge::accept_requests() {
                     case PluginType::vst2:
                         bridge = std::make_unique<Vst2Bridge>(
                             main_context, request.plugin_path,
-                            request.endpoint_base_dir);
+                            request.endpoint_base_dir, request.parent_pid);
                         break;
                     case PluginType::vst3:
 #ifdef WITH_VST3
                         bridge = std::make_unique<Vst3Bridge>(
                             main_context, request.plugin_path,
-                            request.endpoint_base_dir);
+                            request.endpoint_base_dir, request.parent_pid);
 #else
                         throw std::runtime_error(
                             "This version of yabridge has not been compiled "

src/wine-host/bridges/vst2.cpp

@@ -68,8 +68,9 @@ Vst2Bridge& get_bridge_instance(const AEffect* plugin) {
 
 Vst2Bridge::Vst2Bridge(MainContext& main_context,
                        std::string plugin_dll_path,
-                       std::string endpoint_base_dir)
+                       std::string endpoint_base_dir,
-    : HostBridge(main_context, plugin_dll_path),
+                       pid_t parent_pid)
+    : HostBridge(main_context, plugin_dll_path, parent_pid),
       logger(generic_logger),
       plugin_handle(LoadLibrary(plugin_dll_path.c_str()), FreeLibrary),
       sockets(main_context.context, endpoint_base_dir, false) {

src/wine-host/bridges/vst2.h

@@ -47,6 +47,9 @@ class Vst2Bridge : public HostBridge {
      *   to load.
      * @param endpoint_base_dir The base directory used for the socket
      *   endpoints. See `Sockets` for more information.
+     * @param parent_pid The process ID of the native plugin host this bridge is
+     *   supposed to communicate with. Used as part of our watchdog to prevent
+     *   dangling Wine processes.
      *
      * @note The object has to be constructed from the same thread that calls
      *   `main_context.run()`.
@@ -56,7 +59,8 @@ class Vst2Bridge : public HostBridge {
      */
     Vst2Bridge(MainContext& main_context,
                std::string plugin_dll_path,
-               std::string endpoint_base_dir);
+               std::string endpoint_base_dir,
+               pid_t parent_pid);
 
     bool inhibits_event_loop() override;
 

src/wine-host/bridges/vst3.cpp

@@ -89,8 +89,9 @@ InstanceInterfaces::InstanceInterfaces(
 
 Vst3Bridge::Vst3Bridge(MainContext& main_context,
                        std::string plugin_dll_path,
-                       std::string endpoint_base_dir)
+                       std::string endpoint_base_dir,
-    : HostBridge(main_context, plugin_dll_path),
+                       pid_t parent_pid)
+    : HostBridge(main_context, plugin_dll_path, parent_pid),
       logger(generic_logger),
       sockets(main_context.context, endpoint_base_dir, false) {
     std::string error;

src/wine-host/bridges/vst3.h

@@ -207,6 +207,9 @@ class Vst3Bridge : public HostBridge {
      *   load.
      * @param endpoint_base_dir The base directory used for the socket
      *   endpoints. See `Sockets` for more information.
+     * @param parent_pid The process ID of the native plugin host this bridge is
+     *   supposed to communicate with. Used as part of our watchdog to prevent
+     *   dangling Wine processes.
      *
      * @note The object has to be constructed from the same thread that calls
      *   `main_context.run()`.
@@ -216,7 +219,8 @@ class Vst3Bridge : public HostBridge {
      */
     Vst3Bridge(MainContext& main_context,
                std::string plugin_dll_path,
-               std::string endpoint_base_dir);
+               std::string endpoint_base_dir,
+               pid_t parent_pid);
 
     /**
      * For VST3 plugins we'll have to check for every object in

src/wine-host/individual-host.cpp

@@ -82,12 +82,14 @@ __cdecl
         switch (plugin_type) {
             case PluginType::vst2:
                 bridge = std::make_unique<Vst2Bridge>(
-                    main_context, plugin_location, socket_endpoint_path);
+                    main_context, plugin_location, socket_endpoint_path,
+                    parent_pid);
                 break;
             case PluginType::vst3:
 #ifdef WITH_VST3
                 bridge = std::make_unique<Vst3Bridge>(
-                    main_context, plugin_location, socket_endpoint_path);
+                    main_context, plugin_location, socket_endpoint_path,
+                    parent_pid);
 #else
                 std::cerr << "This version of yabridge has not been compiled "
                              "with VST3 support"