refactor: add a syntactic sugar method

Signed-off-by: Phoeniix Zhao <Phoenix500526@163.com>

crates/xline-client/examples/lock.rs

@@ -1,23 +1,33 @@
 use anyhow::Result;
-use xline_client::{clients::Xutex, Client, ClientOptions};
+use xline_client::{
+    clients::Xutex,
+    types::kv::{Compare, CompareResult, PutRequest, TxnOp},
+    Client, ClientOptions,
+};
 
 #[tokio::main]
 async fn main() -> Result<()> {
     // the name and address of all curp members
     let curp_members = ["10.0.0.1:2379", "10.0.0.2:2379", "10.0.0.3:2379"];
 
-    let client = Client::connect(curp_members, ClientOptions::default())
-        .await?
-        .lock_client();
+    let client = Client::connect(curp_members, ClientOptions::default()).await?;
 
-    let mut xutex = Xutex::new(client, "lock-test", None, None).await?;
+    let lock_client = client.lock_client();
+    let kv_client = client.kv_client();
+
+    let mut xutex = Xutex::new(lock_client, "lock-test", None, None).await?;
     // when the `xutex_guard` drop, the lock will be unlocked.
     let xutex_guard = xutex.lock().await?;
 
-    println!(
-        "lock key: {:?}",
-        String::from_utf8_lossy(xutex_guard.key().as_bytes())
-    );
+    let txn_req = xutex_guard
+        .txn_check_locked_key()
+        .when([Compare::value("key2", CompareResult::Equal, "value2")])
+        .and_then([TxnOp::put(
+            PutRequest::new("key2", "value3").with_prev_kv(true),
+        )])
+        .or_else(&[]);
+
+    let _resp = kv_client.txn(txn_req).await?;
 
     Ok(())
 }

crates/xline-client/src/clients/lock.rs

@@ -17,6 +17,7 @@ use crate::{
     error::{Result, XlineClientError},
     lease_gen::LeaseIdGenerator,
     types::{
+        kv::TxnRequest as KvTxnRequest,
         lease::{LeaseGrantRequest, LeaseKeepAliveRequest},
         watch::WatchRequest,
     },
@@ -82,6 +83,24 @@ impl XutexGuard {
     pub fn key(&self) -> &str {
         self.key.as_str()
     }
+
+    /// Return a `TxnRequest` which will perform the success ops when the locked key is exist.
+    /// This method is syntactic sugar
+    #[inline]
+    #[must_use]
+    pub fn txn_check_locked_key(&self) -> KvTxnRequest {
+        let mut txn_request = KvTxnRequest::new();
+        #[allow(clippy::as_conversions)]
+        let cmp = Compare {
+            result: CompareResult::Greater as i32,
+            target: CompareTarget::Create as i32,
+            key: self.key().into(),
+            range_end: Vec::new(),
+            target_union: Some(TargetUnion::CreateRevision(0)),
+        };
+        txn_request.inner.compare.push(cmp);
+        txn_request
+    }
 }
 
 #[async_trait]
@@ -263,6 +282,16 @@ impl Xutex {
     /// ```
     #[inline]
     pub async fn lock(&mut self) -> Result<AsyncDropper<XutexGuard>> {
+        if self
+            .session
+            .keep_alive
+            .as_ref()
+            .is_some_and(JoinHandle::is_finished)
+        {
+            return Err(XlineClientError::LeaseError(String::from(
+                "Lock renew task exists unexpectedly",
+            )));
+        }
         let resp = self.try_acquire().await?;
         #[allow(clippy::indexing_slicing)]
         if let Some(Response::ResponseRange(ref lock_owner)) = resp.responses[1].response {