fix hang issue

Summary: It happens often on BigCache origincache simulation. Let's fail fast instead of hanging there forever.

Reviewed By: AhmedWKamal

Differential Revision: D73675903

fbshipit-source-id: b2070d6d5026a9ddb9a81df00b3f53e597569e0c

Author: jianfeng-tang

cachelib/cachebench/cache/TimeStampTicker.cpp

@@ -39,10 +39,10 @@ bool TimeStampTicker::advanceTimeStamp(uint32_t currTimeStamp) {
   auto currentBucket = currTimeStamp / bucketTicks_;
 
   if (oldBucket > currentBucket) {
-    XLOGF(ERR, "Bucket going BACKWARD from {} to {}", oldBucket, currentBucket);
     // This is an indication that our time-advancing mechanism has a bug.
-    // TODO: Once T85645217 is fixed, throw an exception.
-    return false;
+    // TODO: Fix T85645217.
+    throw std::runtime_error(folly::to<std::string>(
+        "Bucket going BACKWARD from", oldBucket, "to", currentBucket));
   }
 
   // Bucket matches. No update required.