Use separate libusb contexts to avoid thread safety issues

Unfortunately, it appears that using libusb's synchronous transfer API
from several threads causes nasty race conditions in event handling and
can lead to deadlocks, despite the fact that libusb's synchronous API
is documented to be perfectly fine to use from several threads (only
the manual polling functionality is supposed to require special
precautions).

Since usbdk was the only real reason for using a single libusb context
and since usbdk (currently) has so many issues with Dolphin, I think
dropping support for it in order to fix other backends is acceptable.

1 files changed, 7 insertions, 6 deletions

diff --git a/Source/Core/InputCommon/GCAdapter.cpp b/Source/Core/InputCommon/GCAdapter.cpp
index 493d8003f2..f54f85393c 100644
--- a/Source/Core/InputCommon/GCAdapter.cpp
+++ b/Source/Core/InputCommon/GCAdapter.cpp
@@ -72,6 +72,8 @@ static bool s_libusb_hotplug_enabled = false;
 static libusb_hotplug_callback_handle s_hotplug_handle;
 #endif
 
+static LibusbUtils::Context s_libusb_context;
+
 static u8 s_endpoint_in = 0;
 static u8 s_endpoint_out = 0;
 
@@ -147,7 +149,6 @@ static int HotplugCallback(libusb_context* ctx, libusb_device* dev, libusb_hotpl
 
 static void ScanThreadFunc()
 {
-  auto& context = LibusbUtils::GetContext();
   Common::SetCurrentThreadName("GC Adapter Scanning Thread");
   NOTICE_LOG(SERIALINTERFACE, "GC Adapter scanning thread started");
 
@@ -158,7 +159,7 @@ static void ScanThreadFunc()
   if (s_libusb_hotplug_enabled)
   {
     if (libusb_hotplug_register_callback(
-            context,
+            s_libusb_context,
             (libusb_hotplug_event)(LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED |
                                    LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT),
             LIBUSB_HOTPLUG_ENUMERATE, 0x057e, 0x0337, LIBUSB_HOTPLUG_MATCH_ANY, HotplugCallback,
@@ -212,7 +213,7 @@ void StartScanThread()
 {
   if (s_adapter_detect_thread_running.IsSet())
     return;
-  if (!LibusbUtils::GetContext().IsValid())
+  if (!s_libusb_context.IsValid())
     return;
   s_adapter_detect_thread_running.Set(true);
   s_adapter_detect_thread = std::thread(ScanThreadFunc);
@@ -240,7 +241,7 @@ static void Setup()
     s_controller_rumble[i] = 0;
   }
 
-  LibusbUtils::GetContext().GetDeviceList([](libusb_device* device) {
+  s_libusb_context.GetDeviceList([](libusb_device* device) {
     if (CheckDeviceAccess(device))
     {
       // Only connect to a single adapter in case the user has multiple connected
@@ -364,8 +365,8 @@ void Shutdown()
 {
   StopScanThread();
 #if defined(LIBUSB_API_VERSION) && LIBUSB_API_VERSION >= 0x01000102
-  if (LibusbUtils::GetContext().IsValid() && s_libusb_hotplug_enabled)
-    libusb_hotplug_deregister_callback(LibusbUtils::GetContext(), s_hotplug_handle);
+  if (s_libusb_context.IsValid() && s_libusb_hotplug_enabled)
+    libusb_hotplug_deregister_callback(s_libusb_context, s_hotplug_handle);
 #endif
   Reset();