4 files changed, 154 insertions, 12 deletions

diff --git a/al/source.cpp b/al/source.cpp
index 54705e6a..60a9a782 100644
--- a/al/source.cpp
+++ b/al/source.cpp
@@ -486,6 +486,50 @@ inline bool SourceShouldUpdate(ALsource *source, ALCcontext *context)
 }
 
 
+VoiceChange *GetVoiceChangers(ALCcontext *ctx, size_t count)
+{
+    VoiceChange *tail{ctx->mVoiceChangeTail};
+    if UNLIKELY(!count) return tail;
+
+    if(tail == ctx->mCurrentVoiceChange.load(std::memory_order_acquire))
+    {
+        ctx->allocVoiceChanges(count);
+        tail = ctx->mVoiceChangeTail;
+    }
+    else if(count > 1)
+    {
+        VoiceChange *head{tail->mNext.load(std::memory_order_acquire)};
+        size_t avail{1};
+        for(;avail < count;++avail)
+        {
+            if(head == ctx->mCurrentVoiceChange.load(std::memory_order_acquire))
+                break;
+            head = head->mNext.load(std::memory_order_acquire);
+        }
+        if(avail < count)
+        {
+            ctx->allocVoiceChanges(count - avail);
+            tail = ctx->mVoiceChangeTail;
+        }
+    }
+
+    VoiceChange *head{tail};
+    for(size_t avail{1};avail < count;++avail)
+        head = head->mNext.load(std::memory_order_relaxed);
+    ctx->mVoiceChangeTail = head->mNext.exchange(nullptr, std::memory_order_relaxed);
+
+    return tail;
+}
+
+void SendVoiceChangers(ALCcontext *ctx, VoiceChange *tail)
+{
+    VoiceChange *oldhead{ctx->mCurrentVoiceChange.load(std::memory_order_acquire)};
+    while(VoiceChange *next{oldhead->mNext.load(std::memory_order_relaxed)})
+        oldhead = next;
+    oldhead->mNext.store(tail, std::memory_order_release);
+}
+
+
 bool EnsureSources(ALCcontext *context, size_t needed)
 {
     size_t count{std::accumulate(context->mSourceList.cbegin(), context->mSourceList.cend(),
@@ -541,20 +585,16 @@ void FreeSource(ALCcontext *context, ALsource *source)
 
     if(IsPlayingOrPaused(source))
     {
-        ALCdevice *device{context->mDevice.get()};
-        BackendLockGuard _{*device->Backend};
         if(ALvoice *voice{GetSourceVoice(source, context)})
         {
-            voice->mCurrentBuffer.store(nullptr, std::memory_order_relaxed);
-            voice->mLoopBuffer.store(nullptr, std::memory_order_relaxed);
-            voice->mSourceID.store(0u, std::memory_order_relaxed);
-            std::atomic_thread_fence(std::memory_order_release);
-            /* Don't set the voice to stopping if it was already stopped or
-             * stopping.
-             */
-            ALvoice::State oldvstate{ALvoice::Playing};
-            voice->mPlayState.compare_exchange_strong(oldvstate, ALvoice::Stopping,
-                std::memory_order_acq_rel, std::memory_order_acquire);
+            VoiceChange *vchg{GetVoiceChangers(context, 1)};
+
+            voice->mPendingStop.store(true, std::memory_order_relaxed);
+            vchg->mVoice = voice;
+            vchg->mSourceID = id;
+            vchg->mState = AL_STOPPED;
+
+            SendVoiceChangers(context, vchg);
         }
     }
 
diff --git a/alc/alc.cpp b/alc/alc.cpp
index 5752fe17..46e930ad 100644
--- a/alc/alc.cpp
+++ b/alc/alc.cpp
@@ -1642,6 +1642,24 @@ void ALCcontext::processUpdates()
 }
 
 
+void ALCcontext::allocVoiceChanges(size_t addcount)
+{
+    constexpr size_t clustersize{128};
+    /* Convert element count to cluster count. */
+    addcount = (addcount+(clustersize-1)) / clustersize;
+    while(addcount)
+    {
+        VoiceChangeCluster cluster{new VoiceChange[clustersize]};
+        for(size_t i{1};i < clustersize;++i)
+            cluster[i-1].mNext.store(std::addressof(cluster[i]), std::memory_order_relaxed);
+        cluster[clustersize-1].mNext.store(mVoiceChangeTail, std::memory_order_relaxed);
+        mVoiceChangeCluster.emplace_back(std::move(cluster));
+        mVoiceChangeTail = mVoiceChangeCluster.back().get();
+        --addcount;
+    }
+}
+
+
 /* alcSetError
  *
  * Stores the latest ALC device error
@@ -2568,6 +2586,14 @@ void ALCcontext::init()
     }
     mActiveAuxSlots.store(auxslots, std::memory_order_relaxed);
 
+    allocVoiceChanges(1);
+    {
+        VoiceChange *cur{mVoiceChangeTail};
+        while(VoiceChange *next{cur->mNext.load(std::memory_order_relaxed)})
+            cur = next;
+        mCurrentVoiceChange.store(cur, std::memory_order_relaxed);
+    }
+
     mExtensionList = alExtList;
 
 
diff --git a/alc/alcontext.h b/alc/alcontext.h
index ba3942f5..59fda1a7 100644
--- a/alc/alcontext.h
+++ b/alc/alcontext.h
@@ -56,6 +56,17 @@ struct ALcontextProps {
 };
 
 
+struct VoiceChange {
+    ALvoice *mVoice{nullptr};
+    ALuint mSourceID{0};
+    ALenum mState{0};
+
+    std::atomic<VoiceChange*> mNext{nullptr};
+
+    DEF_NEWDEL(VoiceChange)
+};
+
+
 struct SourceSubList {
     uint64_t FreeMask{~0_u64};
     ALsource *Sources{nullptr}; /* 64 */
@@ -128,6 +139,24 @@ struct ALCcontext : public al::intrusive_ref<ALCcontext> {
     std::atomic<ALvoiceProps*> mFreeVoiceProps{nullptr};
     std::atomic<ALeffectslotProps*> mFreeEffectslotProps{nullptr};
 
+    /* Asynchronous voice change actions are processed as a linked list of
+     * VoiceChange objects by the mixer, which is atomically appended to.
+     * However, to avoid allocating each object individually, they're allocated
+     * in clusters that are stored in a vector for easy automatic cleanup.
+     */
+    using VoiceChangeCluster = std::unique_ptr<VoiceChange[]>;
+    al::vector<VoiceChangeCluster> mVoiceChangeCluster;
+
+    /* The voice change tail is the beginning of the "free" elements, up to and
+     * *excluding* the current. If tail==current, there's no free elements and
+     * new ones need to be allocated. The current voice change is the element
+     * last processed, and any after are pending.
+     */
+    VoiceChange *mVoiceChangeTail{};
+    std::atomic<VoiceChange*> mCurrentVoiceChange{};
+
+    void allocVoiceChanges(size_t addcount);
+
     al::vector<ALvoice> mVoices;
 
     using ALeffectslotArray = al::FlexArray<ALeffectslot*>;
diff --git a/alc/alu.cpp b/alc/alu.cpp
index 36d4174a..748338ab 100644
--- a/alc/alu.cpp
+++ b/alc/alu.cpp
@@ -1605,9 +1605,56 @@ void CalcSourceParams(ALvoice *voice, ALCcontext *context, bool force)
 }
 
 
+void SendSourceStateEvent(ALCcontext *context, ALuint id, ALenum state)
+{
+    RingBuffer *ring{context->mAsyncEvents.get()};
+    auto evt_vec = ring->getWriteVector();
+    if(evt_vec.first.len < 1) return;
+
+    AsyncEvent *evt{new (evt_vec.first.buf) AsyncEvent{EventType_SourceStateChange}};
+    evt->u.srcstate.id = id;
+    evt->u.srcstate.state = state;
+
+    ring->writeAdvance(1);
+}
+
+void ProcessVoiceChanges(ALCcontext *ctx)
+{
+    VoiceChange *cur{ctx->mCurrentVoiceChange.load(std::memory_order_acquire)};
+    VoiceChange *next{cur->mNext.load(std::memory_order_acquire)};
+    if(!next) return;
+
+    const ALbitfieldSOFT enabledevt{ctx->mEnabledEvts.load(std::memory_order_acquire)};
+    do {
+        cur = next;
+
+        bool success{false};
+        ALvoice *voice{cur->mVoice};
+        if(cur->mState == AL_INITIAL || cur->mState == AL_STOPPED)
+        {
+            if(voice)
+            {
+                voice->mCurrentBuffer.store(nullptr, std::memory_order_relaxed);
+                voice->mLoopBuffer.store(nullptr, std::memory_order_relaxed);
+                voice->mSourceID.exchange(0u, std::memory_order_relaxed);
+                ALvoice::State oldvstate{ALvoice::Playing};
+                success = voice->mPlayState.compare_exchange_strong(oldvstate, ALvoice::Stopping,
+                    std::memory_order_relaxed, std::memory_order_acquire);
+                voice->mPendingStop.store(false, std::memory_order_release);
+            }
+            success |= (cur->mState == AL_INITIAL);
+        }
+        if(success && (enabledevt&EventType_SourceStateChange))
+            SendSourceStateEvent(ctx, cur->mSourceID, cur->mState);
+    } while((next=cur->mNext.load(std::memory_order_acquire)));
+    ctx->mCurrentVoiceChange.store(cur, std::memory_order_release);
+}
+
 void ProcessParamUpdates(ALCcontext *ctx, const ALeffectslotArray &slots,
     const al::span<ALvoice> voices)
 {
+    ProcessVoiceChanges(ctx);
+
     IncrementRef(ctx->mUpdateCount);
     if LIKELY(!ctx->mHoldUpdates.load(std::memory_order_acquire))
     {