Fix: add_learner() should block forever

The `Raft::add_learner()` method, when invoked with the `blocking`
parameter set to `true`, should block forever until the learner
synchronizes its logs with the leader.

In its current implementation, `add_learner()` calls the `Raft::wait()`
method, which has a default timeout of `500ms`. To achieve the desired
blocking behavior, the default timeout should be increased
significantly.

- Fix: #846

openraft/src/raft.rs

@@ -513,7 +513,7 @@ where
     ///
     /// If the node to add is already a voter or learner, it will still re-add it.
     ///
-    /// A `node` stores the network address of a node. Thus an application does not
+    /// A `node` is able to store the network address of a node. Thus an application does not
     /// need another store for mapping node-id to ip-addr when implementing the RaftNetwork.
     #[tracing::instrument(level = "debug", skip(self, id), fields(target=display(id)))]
     pub async fn add_learner(
@@ -816,6 +816,9 @@ where
 
     /// Get a handle to wait for the metrics to satisfy some condition.
     ///
+    /// If `timeout` is `None`, then it will wait forever(10 years).
+    /// If `timeout` is `Some`, then it will wait for the specified duration.
+    ///
     /// ```ignore
     /// # use std::time::Duration;
     /// # use openraft::{State, Raft};
@@ -834,7 +837,7 @@ where
     pub fn wait(&self, timeout: Option<Duration>) -> Wait<C::NodeId, C::Node> {
         let timeout = match timeout {
             Some(t) => t,
-            None => Duration::from_millis(500),
+            None => Duration::from_secs(86400 * 365 * 100),
         };
         Wait {
             timeout,

tests/tests/membership/t30_commit_joint_config.rs

@@ -1,4 +1,5 @@
 use std::sync::Arc;
+use std::time::Duration;
 
 use anyhow::Result;
 use futures::stream::StreamExt;
@@ -36,7 +37,7 @@ async fn commit_joint_config_during_0_to_012() -> Result<()> {
     // Assert all nodes are in learner state & have no entries.
     let mut log_index = 1;
 
-    router.wait_for_log(&btreeset![0], Some(log_index), None, "init node 0").await?;
+    router.wait_for_log(&btreeset![0], Some(log_index), timeout(), "init node 0").await?;
 
     // Sync some new nodes.
     router.new_raft_node(1).await;
@@ -51,7 +52,7 @@ async fn commit_joint_config_during_0_to_012() -> Result<()> {
     }
     log_index += 2;
 
-    router.wait_for_log(&btreeset![0], Some(log_index), None, "init node 0").await?;
+    router.wait_for_log(&btreeset![0], Some(log_index), timeout(), "init node 0").await?;
 
     tracing::info!(
         log_index,
@@ -76,7 +77,7 @@ async fn commit_joint_config_during_0_to_012() -> Result<()> {
         .wait_for_metrics(
             &0,
             |x| x.last_applied.index() > Some(log_index),
-            None,
+            timeout(),
             "the next joint log should not commit",
         )
         .await;
@@ -134,10 +135,14 @@ async fn commit_joint_config_during_012_to_234() -> Result<()> {
     }
     log_index += 2;
 
-    let wait_rst = router.wait_for_log(&btreeset![0], Some(log_index), None, "cluster of joint").await;
+    let wait_rst = router.wait_for_log(&btreeset![0], Some(log_index), timeout(), "cluster of joint").await;
 
     // the first step of joint should not pass because the new config can not constitute a quorum
     assert!(wait_rst.is_err());
 
     Ok(())
 }
+
+fn timeout() -> Option<Duration> {
+    Some(Duration::from_millis(1_000))
+}