Take locks before signaling thread condition variables (#2636)

src/mbgl/tile/tile_cache.cpp

@@ -53,6 +53,8 @@ void TileCache::deferredRelease(std::unique_ptr<Tile>&& tile) {
     // last one and the destruction actually occurs here on this thread.
     std::function<void()> func{[tile_{CaptureWrapper<Tile>{std::move(tile)}}, this]() mutable {
         tile_.item = {};
+
+        std::lock_guard<std::mutex> counterLock(deferredSignalLock);
         deferredDeletionsPending--;
         deferredSignal.notify_all();
     }};

src/mbgl/tile/tile_cache.hpp

@@ -50,10 +50,9 @@ private:
     std::map<OverscaledTileID, std::unique_ptr<Tile>> tiles;
     std::list<OverscaledTileID> orderedKeys;
     TaggedScheduler threadPool;
-    std::atomic<size_t> deferredDeletionsPending{0};
+    size_t deferredDeletionsPending{0};
     std::mutex deferredSignalLock;
     std::condition_variable deferredSignal;
-
     size_t size;
 };
 

src/mbgl/util/thread_pool.cpp

@@ -130,6 +130,8 @@ void ThreadedSchedulerBase::schedule(const util::SimpleIdentity tag, std::functi
         taskCount++;
     }
 
+    // Take the worker lock before notifying to prevent threads from waiting while we try to wake them
+    std::lock_guard<std::mutex> workerLock(workerMutex);
     cvAvailable.notify_one();
 }