use unit64_t for numElements in HHWheelTimer

Summary: Some compiler will complain about this when calling std::min with a size_t and a uint64_t. So use unit64_t for numElements in HHWheelTimer.

Reviewed By: mzlee

Differential Revision: D3116346

fb-gh-sync-id: 67a9eebf4f9e8fe0e732a7292af55122be04163b
fbshipit-source-id: 67a9eebf4f9e8fe0e732a7292af55122be04163b

folly/io/async/HHWheelTimer.cpp

@@ -229,8 +229,8 @@ size_t HHWheelTimer::cancelAll() {
   size_t count = 0;
 
   if (count_ != 0) {
-    const size_t numElements = WHEEL_BUCKETS * WHEEL_SIZE;
-    size_t maxBuckets = std::min(numElements, count_);
+    const uint64_t numElements = WHEEL_BUCKETS * WHEEL_SIZE;
+    auto maxBuckets = std::min(numElements, count_);
     auto buckets = folly::make_unique<CallbackList[]>(maxBuckets);
     size_t countBuckets = 0;
     for (auto& tick : buckets_) {