[MERGE #4004 @obastemur] numberToString: re-cache on miss and cache more

Merge pull request #4004 from obastemur:bet_num_str_stuff

Improve numberToString cache for long running applications while adding more space to hash table cap.

```
// limit the htable size to NUMBER_TO_STRING_CACHE_SIZE and refresh the cache often
// however don't re-cache if we didn't use it much! App may not be suitable for caching.
// 4% -> NUMBER_TO_STRING_RE_CACHE_REASON_LIMIT is equal to perf loss while we cache the stuff
```

pros;

- no point holding a cache that we may never use again

cons;

- if the application is generating 100% distinct NUMBER_TO_STRING_CACHE_SIZE+1 numbers and stringify them all the time.. well, the perf could be  ~4% slower comparing to now. This is due to cache won't have any use yet we will be filling it up again and again. In order to prevent that, we will check the cache usage and do not re-cache if we didn't even use it.

Author: LouisLaf

lib/Runtime/Base/ScriptContext.cpp

@@ -74,7 +74,12 @@ namespace Js
 #ifdef FAULT_INJECTION
         disposeScriptByFaultInjectionEventHandler(nullptr),
 #endif
+
+#ifndef CC_LOW_MEMORY_TARGET
         integerStringMap(this->GeneralAllocator()),
+        integerStringMapCacheMissCount(0),
+        integerStringMapCacheUseCount(0),
+#endif
         guestArena(nullptr),
         raiseMessageToDebuggerFunctionType(nullptr),
         transitionToDebugModeIfFirstSourceFn(nullptr),
@@ -1753,23 +1758,32 @@ namespace Js
 
 // TODO: (obastemur) Could this be dynamic instead of compile time?
 #ifndef CC_LOW_MEMORY_TARGET // we don't need this on a target with low memory
+#define NUMBER_TO_STRING_CACHE_SIZE 1024
+#define NUMBER_TO_STRING_RE_CACHE_LIMIT 1024
+#define NUMBER_TO_STRING_RE_CACHE_REASON_LIMIT 48
         if (!this->integerStringMap.TryGetValue(value, &string))
         {
             // Add the string to hash table cache
-            // Don't add if table is getting too full.  We'll be holding on to
-            // too many strings, and table lookup will become too slow.
-            // TODO: Long term running app, this cache doesn't provide much value?
-            //       i.e. what is the importance of first 512 number to string calls?
-            //       a solution; count the number of times we couldn't use cache
-            //       after cache is full. If it's bigger than X ?? the discard the
-            //       previous cache?
-            if (this->integerStringMap.Count() > 512)
+            // limit the htable size to NUMBER_TO_STRING_CACHE_SIZE and refresh the cache often
+            // however don't re-cache if we didn't use it much! App may not be suitable for caching.
+            // 4% -> NUMBER_TO_STRING_RE_CACHE_REASON_LIMIT is equal to perf loss while we cache the stuff
+            if (integerStringMapCacheMissCount > NUMBER_TO_STRING_RE_CACHE_LIMIT)
+            {
+                integerStringMapCacheMissCount = 0;
+                if (integerStringMapCacheUseCount >= NUMBER_TO_STRING_RE_CACHE_REASON_LIMIT)
+                {
+                    this->integerStringMap.Clear();
+                }
+                integerStringMapCacheUseCount = 0;
+            }
+
+            if (this->integerStringMap.Count() > NUMBER_TO_STRING_CACHE_SIZE)
             {
 #endif
                 // Use recycler memory
                 string = TaggedInt::ToString(value, this);
-
 #ifndef CC_LOW_MEMORY_TARGET
+                integerStringMapCacheMissCount++;
             }
             else
             {
@@ -1781,6 +1795,10 @@ namespace Js
                 this->integerStringMap.AddNew(value, string);
             }
         }
+        else if (integerStringMapCacheUseCount < NUMBER_TO_STRING_RE_CACHE_REASON_LIMIT)
+        {
+            integerStringMapCacheUseCount++;
+        }
 #endif
 
         return string;

lib/Runtime/Base/ScriptContext.h

@@ -830,7 +830,11 @@ namespace Js
         EventHandler disposeScriptByFaultInjectionEventHandler;
 #endif
 
+#ifndef CC_LOW_MEMORY_TARGET
         JsUtil::BaseDictionary<uint, JavascriptString *, ArenaAllocator> integerStringMap;
+        uint integerStringMapCacheMissCount;
+        uint integerStringMapCacheUseCount;
+#endif
 
         double lastNumberToStringRadix10;
         double lastUtcTimeFromStr;