Move the observed feature collection to the threaded part now that it can be done safely.

src/misc.h

@@ -400,7 +400,7 @@ inline uint64_t mul_hi64(uint64_t a, uint64_t b) {
 // This bitset can be accessed concurrently, provided
 // the concurrent accesses are performed on distinct
 // instances of underlying type. That means the cuncurrent
-// accesses need to be spaced by at least 
+// accesses need to be spaced by at least
 // bits_per_bucket bits.
 // But at least best_concurrent_access_stride bits
 // is recommended to prevent false sharing.
@@ -418,6 +418,11 @@ public:
     constexpr static uint64_t num_buckets = (num_bits + bits_per_bucket - 1) / bits_per_bucket;
     constexpr static uint64_t best_concurrent_access_stride = 8 * cache_line_size;
 
+    LargeBitset()
+    {
+        std::fill(std::begin(bits), std::end(bits), 0);
+    }
+
     void set(uint64_t idx)
     {
         const uint64_t bucket = idx / bits_per_bucket;