api/joystick: reduce mutex contention

Don't look for changes in hotplug joysticks by freezing up polling for
joysticks' axis and button.

Issue: #267

2 files changed, 18 insertions, 7 deletions

diff --git a/opentrack/win32-joystick.cpp b/opentrack/win32-joystick.cpp
index 29a51a43..0bd6bfda 100644
--- a/opentrack/win32-joystick.cpp
+++ b/opentrack/win32-joystick.cpp
@@ -33,9 +33,10 @@ win32_joy_ctx& win32_joy_ctx::make()
 
 void win32_joy_ctx::poll(fn f)
 {
+    refresh(false);
+    
     QMutexLocker l(&mtx);
     
-    refresh(false);
     for (auto& j : joys())
     {
         j.second->poll(f);
@@ -44,10 +45,10 @@ void win32_joy_ctx::poll(fn f)
 
 bool win32_joy_ctx::poll_axis(const QString &guid, int axes[])
 {
-    QMutexLocker l(&mtx);
-    
     refresh(false);
     
+    QMutexLocker l(&mtx);
+    
     auto iter = joys().find(guid);
     
     if (iter == joys().end() || iter->second->joy_handle == nullptr)
@@ -134,12 +135,14 @@ void win32_joy_ctx::refresh(bool first)
 {
     if (!first)
     {
+        QMutexLocker l(&mtx);
+        
         if (timer_joylist.elapsed_ms() < joylist_refresh_ms)
             return;
         timer_joylist.start();
     }
     
-    enum_state st(joys(), first);
+    enum_state st(joys(), first, mtx);
 }
 
 QString win32_joy_ctx::guid_to_string(const GUID guid)
@@ -210,11 +213,16 @@ bool win32_joy_ctx::joy::poll(fn f)
     return true;
 }
 
-win32_joy_ctx::enum_state::enum_state(std::unordered_map<QString, std::shared_ptr<joy> > &joys, bool first) : joys(joys), first(first)
+win32_joy_ctx::enum_state::enum_state(std::unordered_map<QString, std::shared_ptr<joy> > &joys, bool first, QMutex& mtx) : first(first)
 {
     HRESULT hr;
     LPDIRECTINPUT8 di = dinput_handle();
     
+    {
+        QMutexLocker l(&mtx);
+        this->joys = joys;
+    }
+    
     if(FAILED(hr = di->EnumDevices(DI8DEVCLASS_GAMECTRL,
                                    EnumJoysticksCallback,
                                    this,
@@ -231,6 +239,9 @@ win32_joy_ctx::enum_state::enum_state(std::unordered_map<QString, std::shared_pt
         else
             it++;
     }
+    
+    QMutexLocker l(&mtx);
+    joys = this->joys;
 }
 
 win32_joy_ctx::enum_state::EnumJoysticksCallback(const DIDEVICEINSTANCE *pdidInstance, void *pContext)
diff --git a/opentrack/win32-joystick.hpp b/opentrack/win32-joystick.hpp
index 334b617a..3f47d170 100644
--- a/opentrack/win32-joystick.hpp
+++ b/opentrack/win32-joystick.hpp
@@ -100,14 +100,14 @@ private:
 
     class enum_state
     {
-        std::unordered_map<QString, std::shared_ptr<joy>>& joys;
+        std::unordered_map<QString, std::shared_ptr<joy>> joys;
         bool first;
         
         std::vector<QString> all;
         static BOOL CALLBACK EnumJoysticksCallback(const DIDEVICEINSTANCE* pdidInstance, VOID* pContext);
         static BOOL CALLBACK EnumObjectsCallback(const DIDEVICEOBJECTINSTANCE* pdidoi, VOID* ctx);
     public:
-        enum_state(std::unordered_map<QString, std::shared_ptr<joy>>& joys, bool first);
+        enum_state(std::unordered_map<QString, std::shared_ptr<joy>>& joys, bool first, QMutex &mtx);
     };
 };