Only join a previous command thread and restart if it has exited

* APP_CMD_INIT_WINDOW can be called when the application hasn't fully
  shutdown, and the thread is still running. Hold a lock while we're
  inside renderdoccmd() so that we know if the thread has exited or not.
* This would be easier if android had pthread_tryjoin_np()...

renderdoccmd/renderdoccmd_android.cpp

@@ -47,11 +47,26 @@ using std::istringstream;
 struct android_app *android_state;
 pthread_t cmdthread_handle = 0;
 
-struct
+struct PThreadLock
 {
-  pthread_mutex_t lock;
-  pthread_mutexattr_t attr;
-} m_DrawLock;
+  void init()
+  {
+    pthread_mutexattr_init(&mutexattr);
+    pthread_mutexattr_settype(&mutexattr, PTHREAD_MUTEX_RECURSIVE);
+    pthread_mutex_init(&mutex, &mutexattr);
+  }
+  void destroy()
+  {
+    pthread_mutex_destroy(&mutex);
+    pthread_mutexattr_destroy(&mutexattr);
+  }
+  bool trylock() { return pthread_mutex_trylock(&mutex) == 0; };
+  void lock() { pthread_mutex_lock(&mutex); }
+  void unlock() { pthread_mutex_unlock(&mutex); }
+private:
+  pthread_mutex_t mutex;
+  pthread_mutexattr_t mutexattr;
+} m_DrawLock, m_CmdLock;
 
 void Daemonise()
 {
@@ -60,7 +75,7 @@ void Daemonise()
 void DisplayGenericSplash()
 {
   // if something else is drawing and holding the lock, then bail
-  if(pthread_mutex_trylock(&m_DrawLock.lock))
+  if(!m_DrawLock.trylock())
     return;
 
   // since we're not pumping this continually and we only draw when we need to, we can just do the
@@ -275,7 +290,7 @@ void main()
 
   dlclose(libEGL);
 
-  pthread_mutex_unlock(&m_DrawLock.lock);
+  m_DrawLock.unlock();
 }
 
 WindowingData DisplayRemoteServerPreview(bool active, const rdcarray<WindowingSystem> &systems)
@@ -290,11 +305,11 @@ WindowingData DisplayRemoteServerPreview(bool active, const rdcarray<WindowingSy
     // if we're opening it, aquire the draw lock, otherwise release it.
     if(active)
     {
-      pthread_mutex_lock(&m_DrawLock.lock);
+      m_DrawLock.lock();
     }
     else
     {
-      pthread_mutex_unlock(&m_DrawLock.lock);
+      m_DrawLock.unlock();
 
       // when we release it, re-draw the splash
       DisplayGenericSplash();
@@ -314,7 +329,7 @@ void DisplayRendererPreview(IReplayController *renderer, TextureDisplay &display
 {
   ANativeWindow *connectionScreenWindow = android_state->window;
 
-  pthread_mutex_lock(&m_DrawLock.lock);
+  m_DrawLock.lock();
 
   IReplayOutput *out = renderer->CreateOutput(CreateAndroidWindowingData(connectionScreenWindow),
                                               ReplayOutputType::Texture);
@@ -331,7 +346,7 @@ void DisplayRendererPreview(IReplayController *renderer, TextureDisplay &display
     usleep(100000);
   }
 
-  pthread_mutex_unlock(&m_DrawLock.lock);
+  m_DrawLock.unlock();
 }
 
 // Returns the renderdoccmd arguments passed via am start
@@ -377,7 +392,11 @@ void *cmdthread(void *)
 {
   vector<string> args = getRenderdoccmdArgs();
   if(args.size())
+  {
+    m_CmdLock.lock();
     renderdoccmd(GlobalEnvironment(), args);
+    m_CmdLock.unlock();
+  }
 
   // activity is done and should be closed
   ANativeActivity_finish(android_state->activity);
@@ -391,11 +410,26 @@ void handle_cmd(android_app *app, int32_t cmd)
   {
     case APP_CMD_INIT_WINDOW:
     {
+      // if we already have a thread handle, see if it's still running
       if(cmdthread_handle != 0)
-        // If user resumes APK after server shutdown, restart the thread.
-        pthread_join(cmdthread_handle, NULL);
+      {
+        // if the thread isn't running anymore, we can acquire m_CmdLock. If so, we need to join the
+        // thread and start afresh. If we can't acquire the lock, the thread is still running so we
+        // leave it alone.
+        if(m_CmdLock.trylock())
+        {
+          m_CmdLock.unlock();
+          // safe to join here, thread will terminate soon if it hasn't already
+          pthread_join(cmdthread_handle, NULL);
+          cmdthread_handle = 0;
+        }
+      }
 
-      pthread_create(&cmdthread_handle, NULL, cmdthread, NULL);
+      // if we don't have a command thread, start one.
+      if(cmdthread_handle == 0)
+        pthread_create(&cmdthread_handle, NULL, cmdthread, NULL);
+
+      DisplayGenericSplash();
       break;
     }
     case APP_CMD_WINDOW_REDRAW_NEEDED:
@@ -413,9 +447,8 @@ void android_main(struct android_app *state)
   android_state = state;
   android_state->onAppCmd = handle_cmd;
 
-  pthread_mutexattr_init(&m_DrawLock.attr);
-  pthread_mutexattr_settype(&m_DrawLock.attr, PTHREAD_MUTEX_RECURSIVE);
-  pthread_mutex_init(&m_DrawLock.lock, &m_DrawLock.attr);
+  m_DrawLock.init();
+  m_CmdLock.init();
 
   ANDROID_LOG("android_main android_state->window: %p", android_state->window);
 
@@ -433,6 +466,6 @@ void android_main(struct android_app *state)
 
   ANDROID_LOG("android_main exiting");
 
-  pthread_mutex_destroy(&m_DrawLock.lock);
-  pthread_mutexattr_destroy(&m_DrawLock.attr);
+  m_DrawLock.destroy();
+  m_CmdLock.destroy();
 }