server: implement full raft client (tikv#8498)

This is the second PR extracted from tikv#6228. See also tikv#8475.

This PR adds the missing implement of raft client.

Signed-off-by: Jay Lee <BusyJayLee@gmail.com>

components/tikv_util/src/future_pool/mod.rs

@@ -17,7 +17,7 @@ use futures03::channel::oneshot::{self, Canceled};
 use prometheus::{Histogram, IntCounter, IntGauge};
 use yatp::task::future;
 
-type ThreadPool = yatp::ThreadPool<future::TaskCell>;
+pub type ThreadPool = yatp::ThreadPool<future::TaskCell>;
 
 use crate::time::Instant;
 use yatp::pool::Local;

components/tikv_util/src/lru.rs

@@ -229,6 +229,17 @@ where
             None => None,
         }
     }
+
+    #[inline]
+    pub fn get_mut(&mut self, key: &K) -> Option<&mut V> {
+        match self.map.get_mut(key) {
+            Some(v) => {
+                self.trace.maybe_promote(v.record);
+                Some(&mut v.value)
+            }
+            None => None,
+        }
+    }
 }
 
 unsafe impl<K: Send, V: Send> Send for LruCache<K, V> {}