diff --git a/Cargo.toml b/Cargo.toml
index ddb8b29..9b052c5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "colink"
-version = "0.1.21"
+version = "0.1.22"
 edition = "2021"
 description = "CoLink Rust SDK"
 license = "MIT"
diff --git a/README.md b/README.md
index 3a6b6b0..354fbec 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@ CoLink SDK helps both application adnd protocol developers access the functional
 Add this to your Cargo.toml:
 ```toml
 [dependencies]
-colink = "0.1.21"
+colink = "0.1.22"
 ```
 
 ## Getting Started
@@ -38,6 +38,9 @@ cargo run --example user_run_task http://localhost:8080 $(sed -n "1,2p" ~/.colin
 cargo run --example host_import_user <address> <host_jwt> <expiration_timestamp> # <expiration_timestamp> is optional
 ```
 ```
+cargo run --example host_import_users <address> <host_jwt> <number> <expiration_timestamp> # <expiration_timestamp> is optional
+```
+```
 cargo run --example host_import_users_and_exchange_guest_jwts <address> <host_jwt> <number> <expiration_timestamp> # <expiration_timestamp> is optional
 ```
 ```
@@ -85,6 +88,9 @@ cargo run --example user_start_protocol_operator <address> <user_jwt> <protocol_
 ```
 cargo run --example user_stop_protocol_operator <address> <user_jwt> <instance_id>
 ```
+```
+cargo run --example user_wait_task <address> <user_jwt> <target_user_id>
+```
 
 ### Protocol
 ```
diff --git a/examples/auto_confirm.rs b/examples/auto_confirm.rs
index cdb9eaa..ae3c80e 100644
--- a/examples/auto_confirm.rs
+++ b/examples/auto_confirm.rs
@@ -1,4 +1,7 @@
-use colink::{CoLink, CoLinkInternalTaskIdList, StorageEntry, SubscriptionMessage, Task};
+use colink::{
+    utils::get_path_timestamp, CoLink, CoLinkInternalTaskIdList, StorageEntry, SubscriptionMessage,
+    Task,
+};
 use prost::Message;
 use std::env;
 use tracing::debug;
@@ -37,11 +40,11 @@ async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>
             let list_entry = &res[0];
             let list: CoLinkInternalTaskIdList = Message::decode(&*list_entry.payload).unwrap();
             if list.task_ids_with_key_paths.is_empty() {
-                get_timestamp(&list_entry.key_path)
+                get_path_timestamp(&list_entry.key_path)
             } else {
                 list.task_ids_with_key_paths
                     .iter()
-                    .map(|x| get_timestamp(&x.key_path))
+                    .map(|x| get_path_timestamp(&x.key_path))
                     .min()
                     .unwrap_or(i64::MAX)
             }
@@ -75,8 +78,3 @@ async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>
         }
     }
 }
-
-fn get_timestamp(key_path: &str) -> i64 {
-    let pos = key_path.rfind('@').unwrap();
-    key_path[pos + 1..].parse().unwrap()
-}
diff --git a/examples/user_wait_task.rs b/examples/user_wait_task.rs
new file mode 100644
index 0000000..aa842fb
--- /dev/null
+++ b/examples/user_wait_task.rs
@@ -0,0 +1,37 @@
+use colink::{
+    decode_jwt_without_validation, extensions::registry::UserRecord, CoLink, Participant,
+};
+use prost::Message;
+use std::env;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>> {
+    let args = env::args().skip(1).collect::<Vec<_>>();
+    let addr = &args[0];
+    let jwt = &args[1];
+    let target_user = &args[2];
+    let user_id = decode_jwt_without_validation(jwt).unwrap().user_id;
+
+    let user = UserRecord {
+        user_id: target_user.to_string(),
+        ..Default::default()
+    };
+    let mut payload = vec![];
+    user.encode(&mut payload).unwrap();
+    let cl = CoLink::new(addr, jwt);
+    let participants = vec![Participant {
+        user_id: user_id.to_string(),
+        role: "query_from_registries".to_string(),
+    }];
+    let task_id = cl
+        .run_task("registry", target_user.as_bytes(), &participants, false)
+        .await?;
+    println!(
+        "Task {} has been created, waiting for it to finish...",
+        task_id
+    );
+    cl.wait_task(&task_id).await?;
+    println!("Task {} finished", task_id);
+
+    Ok(())
+}
diff --git a/src/extensions/policy_module.rs b/src/extensions/policy_module.rs
index 80f5468..65801c8 100644
--- a/src/extensions/policy_module.rs
+++ b/src/extensions/policy_module.rs
@@ -1,4 +1,4 @@
-use crate::colink_proto::*;
+use crate::{colink_proto::*, utils::get_path_timestamp};
 pub use colink_policy_module_proto::*;
 use prost::Message;
 mod colink_policy_module_proto {
@@ -19,7 +19,7 @@ impl crate::application::CoLink {
         {
             Ok(res) => (
                 prost::Message::decode(&*res[0].payload)?,
-                get_timestamp(&res[0].key_path),
+                get_path_timestamp(&res[0].key_path),
             ),
             Err(_) => (Default::default(), 0),
         };
@@ -30,7 +30,7 @@ impl crate::application::CoLink {
         settings.enable = true;
         let mut payload = vec![];
         settings.encode(&mut payload).unwrap();
-        let timestamp = get_timestamp(
+        let timestamp = get_path_timestamp(
             &self
                 .update_entry("_policy_module:settings", &payload)
                 .await?,
@@ -58,7 +58,7 @@ impl crate::application::CoLink {
         settings.enable = false;
         let mut payload = vec![];
         settings.encode(&mut payload).unwrap();
-        let timestamp = get_timestamp(
+        let timestamp = get_path_timestamp(
             &self
                 .update_entry("_policy_module:settings", &payload)
                 .await?,
@@ -88,7 +88,7 @@ impl crate::application::CoLink {
         settings.rules.push(rule);
         let mut payload = vec![];
         settings.encode(&mut payload).unwrap();
-        let timestamp = get_timestamp(
+        let timestamp = get_path_timestamp(
             &self
                 .update_entry("_policy_module:settings", &payload)
                 .await?,
@@ -109,7 +109,7 @@ impl crate::application::CoLink {
         settings.rules.retain(|x| x.rule_id != rule_id);
         let mut payload = vec![];
         settings.encode(&mut payload).unwrap();
-        let timestamp = get_timestamp(
+        let timestamp = get_path_timestamp(
             &self
                 .update_entry("_policy_module:settings", &payload)
                 .await?,
@@ -136,7 +136,7 @@ impl crate::application::CoLink {
                 if applied_settings_timestamp >= timestamp {
                     return Ok(());
                 }
-                get_timestamp(&res[0].key_path) + 1
+                get_path_timestamp(&res[0].key_path) + 1
             }
             Err(_) => 0,
         };
@@ -157,8 +157,3 @@ impl crate::application::CoLink {
         Ok(())
     }
 }
-
-fn get_timestamp(key_path: &str) -> i64 {
-    let pos = key_path.rfind('@').unwrap();
-    key_path[pos + 1..].parse().unwrap()
-}
diff --git a/src/extensions/registry.rs b/src/extensions/registry.rs
index f8553ac..35c3572 100644
--- a/src/extensions/registry.rs
+++ b/src/extensions/registry.rs
@@ -1,5 +1,5 @@
 use crate::colink_proto::*;
-pub use colink_registry_proto::{Registries, Registry};
+pub use colink_registry_proto::{Registries, Registry, UserRecord};
 use prost::Message;
 mod colink_registry_proto {
     include!(concat!(env!("OUT_DIR"), "/colink_registry.rs"));
diff --git a/src/extensions/wait_task.rs b/src/extensions/wait_task.rs
index d7a78d4..61fef12 100644
--- a/src/extensions/wait_task.rs
+++ b/src/extensions/wait_task.rs
@@ -1,4 +1,4 @@
-use crate::colink_proto::*;
+use crate::{colink_proto::*, utils::get_path_timestamp};
 use prost::Message;
 use tracing::debug;
 
@@ -19,7 +19,7 @@ impl crate::application::CoLink {
                 if task.status == "finished" {
                     return Ok(());
                 }
-                get_timestamp(&res[0].key_path) + 1
+                get_path_timestamp(&res[0].key_path) + 1
             }
             Err(_) => 0,
         };
@@ -40,8 +40,3 @@ impl crate::application::CoLink {
         Ok(())
     }
 }
-
-fn get_timestamp(key_path: &str) -> i64 {
-    let pos = key_path.rfind('@').unwrap();
-    key_path[pos + 1..].parse().unwrap()
-}
diff --git a/src/lib.rs b/src/lib.rs
index dcd5f3a..f597140 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -12,3 +12,4 @@ pub use protocol::{
     CoLinkProtocol, ProtocolEntry, _colink_parse_args, _protocol_start, async_trait,
 };
 pub mod extensions;
+pub mod utils;
diff --git a/src/protocol.rs b/src/protocol.rs
index e1013fb..4324908 100644
--- a/src/protocol.rs
+++ b/src/protocol.rs
@@ -1,4 +1,4 @@
-use crate::application::*;
+use crate::{application::*, utils::get_path_timestamp};
 pub use async_trait::async_trait;
 use futures_lite::stream::StreamExt;
 use lapin::{
@@ -7,7 +7,11 @@ use lapin::{
     Connection, ConnectionProperties,
 };
 use prost::Message;
-use std::{collections::HashMap, sync::mpsc::channel, thread};
+use std::{
+    collections::{HashMap, HashSet},
+    sync::{mpsc::channel, Arc, Mutex},
+    thread,
+};
 use structopt::StructOpt;
 use tracing::{debug, error};
 
@@ -71,11 +75,11 @@ impl CoLinkProtocol {
                         let list: CoLinkInternalTaskIdList =
                             Message::decode(&*list_entry.payload).unwrap();
                         if list.task_ids_with_key_paths.is_empty() {
-                            get_timestamp(&list_entry.key_path)
+                            get_path_timestamp(&list_entry.key_path)
                         } else {
                             list.task_ids_with_key_paths
                                 .iter()
-                                .map(|x| get_timestamp(&x.key_path))
+                                .map(|x| get_path_timestamp(&x.key_path))
                                 .min()
                                 .unwrap_or(i64::MAX)
                         }
@@ -151,19 +155,16 @@ impl CoLinkProtocol {
     }
 }
 
-fn get_timestamp(key_path: &str) -> i64 {
-    let pos = key_path.rfind('@').unwrap();
-    key_path[pos + 1..].parse().unwrap()
-}
-
 pub fn _protocol_start(
     cl: CoLink,
     user_funcs: HashMap<String, Box<dyn ProtocolEntry + Send + Sync>>,
 ) -> Result<(), Error> {
     let mut operator_funcs: HashMap<String, Box<dyn ProtocolEntry + Send + Sync>> = HashMap::new();
-    let mut protocols = vec![];
+    let mut protocols = HashSet::new();
+    let failed_protocols = Arc::new(Mutex::new(HashSet::new()));
     for (protocol_and_role, user_func) in user_funcs {
         let cl = cl.clone();
+        let failed_protocols = failed_protocols.clone();
         if protocol_and_role.ends_with(":@init") {
             let protocol_name = protocol_and_role[..protocol_and_role.len() - 6].to_string();
             tokio::runtime::Builder::new_multi_thread()
@@ -181,19 +182,27 @@ pub fn _protocol_start(
                             .start(cl_clone, Default::default(), Default::default())
                             .await
                         {
-                            Ok(_) => {}
-                            Err(e) => error!("{}: {}.", protocol_and_role, e),
+                            Ok(_) => {
+                                cl.update_entry(&is_initialized_key, &[1]).await?;
+                            }
+                            Err(e) => {
+                                error!("{}: {}.", protocol_and_role, e);
+                                failed_protocols.lock().unwrap().insert(protocol_name);
+                            }
                         }
-                        cl.update_entry(&is_initialized_key, &[1]).await?;
                     }
                     cl.unlock(lock).await?;
                     Ok::<(), Box<dyn std::error::Error + Send + Sync + 'static>>(())
                 })?;
         } else {
-            protocols.push(protocol_and_role[..protocol_and_role.rfind(':').unwrap()].to_string());
+            protocols
+                .insert(protocol_and_role[..protocol_and_role.rfind(':').unwrap()].to_string());
             operator_funcs.insert(protocol_and_role, user_func);
         }
     }
+    for failed_protocol in &*failed_protocols.lock().unwrap() {
+        protocols.remove(failed_protocol);
+    }
     let cl_clone = cl.clone();
     tokio::runtime::Builder::new_multi_thread()
         .enable_all()
@@ -259,6 +268,7 @@ pub struct CommandLineArgs {
 }
 
 pub fn _colink_parse_args() -> CoLink {
+    tracing_subscriber::fmt::init();
     let CommandLineArgs {
         addr,
         jwt,
diff --git a/src/utils.rs b/src/utils.rs
new file mode 100644
index 0000000..5beb6f0
--- /dev/null
+++ b/src/utils.rs
@@ -0,0 +1,4 @@
+pub fn get_path_timestamp(key_path: &str) -> i64 {
+    let pos = key_path.rfind('@').unwrap();
+    key_path[pos + 1..].parse().unwrap()
+}