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.

8 files changed, 16 insertions, 26 deletions

diff --git a/Source/Core/Core/IOS/USB/Bluetooth/BTReal.cpp b/Source/Core/Core/IOS/USB/Bluetooth/BTReal.cpp
index 7ccd5c4fac..b4322681d7 100644
--- a/Source/Core/Core/IOS/USB/Bluetooth/BTReal.cpp
+++ b/Source/Core/Core/IOS/USB/Bluetooth/BTReal.cpp
@@ -28,7 +28,6 @@
 #include "Core/Core.h"
 #include "Core/HW/Memmap.h"
 #include "Core/IOS/Device.h"
-#include "Core/LibusbUtils.h"
 #include "VideoCommon/OnScreenDisplay.h"
 
 namespace IOS::HLE::Device
@@ -75,11 +74,10 @@ BluetoothReal::~BluetoothReal()
 
 IPCCommandResult BluetoothReal::Open(const OpenRequest& request)
 {
-  auto& context = LibusbUtils::GetContext();
-  if (!context.IsValid())
+  if (!m_context.IsValid())
     return GetDefaultReply(IPC_EACCES);
 
-  context.GetDeviceList([this](libusb_device* device) {
+  m_context.GetDeviceList([this](libusb_device* device) {
     libusb_device_descriptor device_descriptor;
     libusb_get_device_descriptor(device, &device_descriptor);
     auto config_descriptor = LibusbUtils::MakeConfigDescriptor(device);
diff --git a/Source/Core/Core/IOS/USB/Bluetooth/BTReal.h b/Source/Core/Core/IOS/USB/Bluetooth/BTReal.h
index 5070cbee75..a1986638ea 100644
--- a/Source/Core/Core/IOS/USB/Bluetooth/BTReal.h
+++ b/Source/Core/Core/IOS/USB/Bluetooth/BTReal.h
@@ -19,6 +19,7 @@
 #include "Core/IOS/USB/Bluetooth/BTBase.h"
 #include "Core/IOS/USB/Bluetooth/hci.h"
 #include "Core/IOS/USB/USBV0.h"
+#include "Core/LibusbUtils.h"
 
 class PointerWrap;
 struct libusb_device;
@@ -70,6 +71,7 @@ private:
   std::atomic<SyncButtonState> m_sync_button_state{SyncButtonState::Unpressed};
   Common::Timer m_sync_button_held_timer;
 
+  LibusbUtils::Context m_context;
   libusb_device* m_device = nullptr;
   libusb_device_handle* m_handle = nullptr;
 
diff --git a/Source/Core/Core/IOS/USB/Host.cpp b/Source/Core/Core/IOS/USB/Host.cpp
index 15308d2b4e..710d26919c 100644
--- a/Source/Core/Core/IOS/USB/Host.cpp
+++ b/Source/Core/Core/IOS/USB/Host.cpp
@@ -24,7 +24,6 @@
 #include "Core/Core.h"
 #include "Core/IOS/USB/Common.h"
 #include "Core/IOS/USB/LibusbDevice.h"
-#include "Core/LibusbUtils.h"
 
 namespace IOS::HLE::Device
 {
@@ -121,10 +120,9 @@ bool USBHost::AddNewDevices(std::set<u64>& new_devices, DeviceChangeHooks& hooks
   if (SConfig::GetInstance().m_usb_passthrough_devices.empty())
     return true;
 
-  auto& context = LibusbUtils::GetContext();
-  if (context.IsValid())
+  if (m_context.IsValid())
   {
-    context.GetDeviceList([&](libusb_device* device) {
+    m_context.GetDeviceList([&](libusb_device* device) {
       libusb_device_descriptor descriptor;
       libusb_get_device_descriptor(device, &descriptor);
       const std::pair<u16, u16> vid_pid = {descriptor.idVendor, descriptor.idProduct};
diff --git a/Source/Core/Core/IOS/USB/Host.h b/Source/Core/Core/IOS/USB/Host.h
index 40e42193d2..d1d0864097 100644
--- a/Source/Core/Core/IOS/USB/Host.h
+++ b/Source/Core/Core/IOS/USB/Host.h
@@ -20,6 +20,7 @@
 #include "Core/IOS/Device.h"
 #include "Core/IOS/IOS.h"
 #include "Core/IOS/USB/Common.h"
+#include "Core/LibusbUtils.h"
 
 class PointerWrap;
 
@@ -71,5 +72,6 @@ private:
   std::thread m_scan_thread;
   Common::Event m_first_scan_complete_event;
   bool m_has_initialised = false;
+  LibusbUtils::Context m_context;
 };
 }  // namespace IOS::HLE::Device
diff --git a/Source/Core/Core/LibusbUtils.cpp b/Source/Core/Core/LibusbUtils.cpp
index 2ee7838c33..a4083e2d06 100644
--- a/Source/Core/Core/LibusbUtils.cpp
+++ b/Source/Core/Core/LibusbUtils.cpp
@@ -109,12 +109,6 @@ bool Context::GetDeviceList(GetDeviceListCallback callback)
   return m_impl->GetDeviceList(std::move(callback));
 }
 
-Context& GetContext()
-{
-  static Context s_context;
-  return s_context;
-}
-
 ConfigDescriptor MakeConfigDescriptor(libusb_device* device, u8 config_num)
 {
 #if defined(__LIBUSB__)
diff --git a/Source/Core/Core/LibusbUtils.h b/Source/Core/Core/LibusbUtils.h
index ded3bd9940..487ba99060 100644
--- a/Source/Core/Core/LibusbUtils.h
+++ b/Source/Core/Core/LibusbUtils.h
@@ -38,11 +38,6 @@ private:
   std::unique_ptr<Impl> m_impl;
 };
 
-// Use this to get a libusb context. Do *not* use any other context
-// because some libusb backends such as UsbDk only work properly with a single context.
-// Additionally, device lists must be retrieved using GetDeviceList for thread safety reasons.
-Context& GetContext();
-
 using ConfigDescriptor = UniquePtr<libusb_config_descriptor>;
 ConfigDescriptor MakeConfigDescriptor(libusb_device* device, u8 config_num = 0);
 }  // namespace LibusbUtils
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();
 
diff --git a/Source/Core/UICommon/USBUtils.cpp b/Source/Core/UICommon/USBUtils.cpp
index 42cf815a12..fe7ad51344 100644
--- a/Source/Core/UICommon/USBUtils.cpp
+++ b/Source/Core/UICommon/USBUtils.cpp
@@ -35,7 +35,7 @@ std::map<std::pair<u16, u16>, std::string> GetInsertedDevices()
   std::map<std::pair<u16, u16>, std::string> devices;
 
 #ifdef __LIBUSB__
-  auto& context = LibusbUtils::GetContext();
+  LibusbUtils::Context context;
   if (!context.IsValid())
     return devices;