From 0b0e7eaf96756d60ba6b8736536bc5729a25fcbe Mon Sep 17 00:00:00 2001
From: Matthias <xmatthias@outlook.com>
Date: Tue, 16 Aug 2022 19:43:41 +0200
Subject: [PATCH] Mutex TTL Cache accesses which can be accessed by multiple
 threads

Apparently, cachetools is (intentionally) not threadsafe
when using the Caches directly.
It's therefore recommended to wrap these with an explicit lock to avoid
problems.

source: https://github.com/tkem/cachetools/issues/245

closes #7215
---
 freqtrade/exchange/exchange.py | 24 ++++++++++++++++--------
 freqtrade/optimize/hyperopt.py |  1 +
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/freqtrade/exchange/exchange.py b/freqtrade/exchange/exchange.py
index d50007dab..d74a01f8b 100644
--- a/freqtrade/exchange/exchange.py
+++ b/freqtrade/exchange/exchange.py
@@ -116,6 +116,7 @@ class Exchange:
         self._last_markets_refresh: int = 0
 
         # Cache for 10 minutes ...
+        self._cache_lock = Lock()
         self._fetch_tickers_cache: TTLCache = TTLCache(maxsize=2, ttl=60 * 10)
         # Cache values for 1800 to avoid frequent polling of the exchange for prices
         # Caching only applies to RPC methods, so prices for open trades are still
@@ -1388,12 +1389,14 @@ class Exchange:
         if not self.exchange_has('fetchBidsAsks'):
             return {}
         if cached:
-            tickers = self._fetch_tickers_cache.get('fetch_bids_asks')
+            with self._cache_lock:
+                tickers = self._fetch_tickers_cache.get('fetch_bids_asks')
             if tickers:
                 return tickers
         try:
             tickers = self._api.fetch_bids_asks(symbols)
-            self._fetch_tickers_cache['fetch_bids_asks'] = tickers
+            with self._cache_lock:
+                self._fetch_tickers_cache['fetch_bids_asks'] = tickers
             return tickers
         except ccxt.NotSupported as e:
             raise OperationalException(
@@ -1414,12 +1417,14 @@ class Exchange:
         :return: fetch_tickers result
         """
         if cached:
-            tickers = self._fetch_tickers_cache.get('fetch_tickers')
+            with self._cache_lock:
+                tickers = self._fetch_tickers_cache.get('fetch_tickers')
             if tickers:
                 return tickers
         try:
             tickers = self._api.fetch_tickers(symbols)
-            self._fetch_tickers_cache['fetch_tickers'] = tickers
+            with self._cache_lock:
+                self._fetch_tickers_cache['fetch_tickers'] = tickers
             return tickers
         except ccxt.NotSupported as e:
             raise OperationalException(
@@ -1528,7 +1533,8 @@ class Exchange:
 
         cache_rate: TTLCache = self._entry_rate_cache if side == "entry" else self._exit_rate_cache
         if not refresh:
-            rate = cache_rate.get(pair)
+            with self._cache_lock:
+                rate = cache_rate.get(pair)
             # Check if cache has been invalidated
             if rate:
                 logger.debug(f"Using cached {side} rate for {pair}.")
@@ -1573,7 +1579,8 @@ class Exchange:
 
         if rate is None:
             raise PricingError(f"{name}-Rate for {pair} was empty.")
-        cache_rate[pair] = rate
+        with self._cache_lock:
+            cache_rate[pair] = rate
 
         return rate
 
@@ -1581,8 +1588,9 @@ class Exchange:
         entry_rate = None
         exit_rate = None
         if not refresh:
-            entry_rate = self._entry_rate_cache.get(pair)
-            exit_rate = self._exit_rate_cache.get(pair)
+            with self._cache_lock:
+                entry_rate = self._entry_rate_cache.get(pair)
+                exit_rate = self._exit_rate_cache.get(pair)
             if entry_rate:
                 logger.debug(f"Using cached buy rate for {pair}.")
             if exit_rate:
diff --git a/freqtrade/optimize/hyperopt.py b/freqtrade/optimize/hyperopt.py
index 566412f29..cbcf39131 100644
--- a/freqtrade/optimize/hyperopt.py
+++ b/freqtrade/optimize/hyperopt.py
@@ -483,6 +483,7 @@ class Hyperopt:
         self.backtesting.exchange._api_async = None
         self.backtesting.exchange.loop = None  # type: ignore
         self.backtesting.exchange._loop_lock = None  # type: ignore
+        self.backtesting.exchange._cache_lock = None  # type: ignore
         # self.backtesting.exchange = None  # type: ignore
         self.backtesting.pairlists = None  # type: ignore