From 605d52f16052f8d0d52e374d73de46f8543cb056 Mon Sep 17 00:00:00 2001
From: Cameron Gutman <aicommander@gmail.com>
Date: Sat, 22 Sep 2018 20:03:41 -0700
Subject: [PATCH] Don't block in audio/video renderer callbacks while the
 renderer is being destroyed

---
 app/streaming/audio/audio.cpp | 17 +++++++++-------
 app/streaming/session.cpp     | 38 +++++++++++++++++++++--------------
 2 files changed, 33 insertions(+), 22 deletions(-)

diff --git a/app/streaming/audio/audio.cpp b/app/streaming/audio/audio.cpp
index df9d0e15..49dce3d1 100644
--- a/app/streaming/audio/audio.cpp
+++ b/app/streaming/audio/audio.cpp
@@ -120,13 +120,16 @@ void Session::arDecodeAndPlaySample(char* sampleData, int sampleLength)
                                              SAMPLES_PER_FRAME,
                                              0);
     if (samplesDecoded > 0) {
-        SDL_AtomicLock(&s_ActiveSession->m_AudioRendererLock);
-        if (s_ActiveSession->m_AudioRenderer != nullptr) {
-            s_ActiveSession->m_AudioRenderer->submitAudio(s_ActiveSession->m_OpusDecodeBuffer,
-                                                          static_cast<int>(sizeof(short) *
-                                                            samplesDecoded *
-                                                            s_ActiveSession->m_AudioConfig.channelCount));
+        // If we can't acquire the lock, that means we're being destroyed
+        // so don't even bother trying to wait.
+        if (SDL_AtomicTryLock(&s_ActiveSession->m_AudioRendererLock)) {
+            if (s_ActiveSession->m_AudioRenderer != nullptr) {
+                s_ActiveSession->m_AudioRenderer->submitAudio(s_ActiveSession->m_OpusDecodeBuffer,
+                                                              static_cast<int>(sizeof(short) *
+                                                                samplesDecoded *
+                                                                s_ActiveSession->m_AudioConfig.channelCount));
+            }
+            SDL_AtomicUnlock(&s_ActiveSession->m_AudioRendererLock);
         }
-        SDL_AtomicUnlock(&s_ActiveSession->m_AudioRendererLock);
     }
 }
diff --git a/app/streaming/session.cpp b/app/streaming/session.cpp
index a6369f0f..94b2c2d7 100644
--- a/app/streaming/session.cpp
+++ b/app/streaming/session.cpp
@@ -170,25 +170,33 @@ int Session::drSubmitDecodeUnit(PDECODE_UNIT du)
     // Use a lock since we'll be yanking this decoder out
     // from underneath the session when we initiate destruction.
     // We need to destroy the decoder on the main thread to satisfy
-    // some API constraints (like DXVA2).
+    // some API constraints (like DXVA2). If we can't acquire it,
+    // that means the decoder is about to be destroyed, so we can
+    // safely return DR_OK and wait for m_NeedsIdr to be set by
+    // the decoder reinitialization code.
 
-    SDL_AtomicLock(&s_ActiveSession->m_DecoderLock);
+    if (SDL_AtomicTryLock(&s_ActiveSession->m_DecoderLock)) {
+        if (s_ActiveSession->m_NeedsIdr) {
+            // If we reset our decoder, we'll need to request an IDR frame
+            s_ActiveSession->m_NeedsIdr = false;
+            SDL_AtomicUnlock(&s_ActiveSession->m_DecoderLock);
+            return DR_NEED_IDR;
+        }
 
-    if (s_ActiveSession->m_NeedsIdr) {
-        // If we reset our decoder, we'll need to request an IDR frame
-        s_ActiveSession->m_NeedsIdr = false;
-        SDL_AtomicUnlock(&s_ActiveSession->m_DecoderLock);
-        return DR_NEED_IDR;
-    }
-
-    IVideoDecoder* decoder = s_ActiveSession->m_VideoDecoder;
-    if (decoder != nullptr) {
-        int ret = decoder->submitDecodeUnit(du);
-        SDL_AtomicUnlock(&s_ActiveSession->m_DecoderLock);
-        return ret;
+        IVideoDecoder* decoder = s_ActiveSession->m_VideoDecoder;
+        if (decoder != nullptr) {
+            int ret = decoder->submitDecodeUnit(du);
+            SDL_AtomicUnlock(&s_ActiveSession->m_DecoderLock);
+            return ret;
+        }
+        else {
+            SDL_AtomicUnlock(&s_ActiveSession->m_DecoderLock);
+            return DR_OK;
+        }
     }
     else {
-        SDL_AtomicUnlock(&s_ActiveSession->m_DecoderLock);
+        // Decoder is going away. Ignore anything coming in until
+        // the lock is released.
         return DR_OK;
     }
 }