Add sync::Barrier (#18)

https://github.com/orgs/rust-micro/projects/2?pane=issue&itemId=38103275

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
+## 0.2.4 - 2023-10-29
+
+- add Barrier type, which implements a barrier for sync based on Redis
+
 ## 0.2.3 - 2023-10-29
 
 - add RwLock Type, which implements a reader-writer lock based on Redis

src/redis/barrier.rs

@@ -0,0 +1,314 @@
+/// The waiting script.
+/// Is is used to indicate, if there is a thread waiting for the barrier.
+/// Returns 1 if #num thread waiting >= #num threads that should wait. Otherwise 0.
+/// If the thread is the leader, it returns 2.
+/// Needs to be used n a loop to update expiration time to signal your wait.
+///
+/// Takes 4 arguments:
+/// 1. The key of the barrier.
+/// 2. The id of the barrier itself.
+/// 3. The number of threads that should wait for the barrier.
+/// 4. The timeout in seconds.
+const WAITING_SCRIPT: &str = r#"
+redis.call("set", ARGV[1] .. ":waiting:" .. ARGV[2], 1, "EX", ARGV[4])
+
+local leader_id = redis.call("get", ARGV[1] .. ":leader")
+if leader_id then
+    if leader_id == ARGV[2] then
+        return 2
+    end
+    return 1
+end
+
+local count = 0
+local cursor = "0"
+
+repeat
+    local res = redis.call("scan", cursor, "MATCH", ARGV[1] .. ":waiting:*", "COUNT", ARGV[3] + 1)
+    if next(res[2]) ~= nil then
+        count = count + #res[2]
+    end
+    cursor = res[1]
+until cursor == "0"
+
+if count < tonumber(ARGV[3]) then
+    return 0
+end
+
+if not leader_id then
+    if redis.call("set", ARGV[1] .. ":leader" , ARGV[2], "EX", ARGV[4], "NX") then
+        return 2
+    end
+end
+
+return 1
+"#;
+
+/// The reset script.
+/// It is used to reset the barrier, so you can reuse it.
+/// Essentially it deletes all keys that are used by the barrier.
+///
+/// Takes 1 Argument:
+/// 1. The key of the value to lock.
+/// 2. The uuid of the barrier.
+/// 3. The number of threads that should wait for the barrier.
+const RESET_SCRIPT: &str = r#"
+redis.call("del", ARGV[1] .. ":waiting:" .. ARGV[2])
+
+local count = 0
+local cursor = "0"
+
+repeat
+    local res = redis.call("scan", cursor, "MATCH", ARGV[1] .. ":waiting:*", "COUNT", ARGV[3] + 1)
+    if next(res[2]) ~= nil then
+        count = count + #res[2]
+    end
+    cursor = res[1]
+until cursor == "0"
+
+-- if it is the last barrier, delete the leader and uuids key
+if count == 0 then
+    redis.call("del", ARGV[1] .. ":leader")
+    redis.call("del", ARGV[1] .. ":uuids")
+end
+"#;
+
+/// The uuid script.
+/// It is used to generate a uuid for the barrier.
+/// It is a very simple counter that is stored in Redis and returns all numbers only once.
+///
+/// Takes 1 Argument:
+/// 1. The key of the value to lock.
+const UUID_SCRIPT: &str = r#"
+redis.call("incr", ARGV[1] .. ":uuids")
+local val = redis.call("get", ARGV[1] .. ":uuids")
+return val
+"#;
+
+pub struct Barrier {
+    uuid: usize,
+    num: usize,
+    key: String,
+    _client: redis::Client,
+    conn: Option<redis::Connection>,
+}
+
+#[derive(PartialEq)]
+enum RedisBarrierStatus {
+    Waiting,
+    Leader,
+    Done,
+}
+
+impl From<u8> for RedisBarrierStatus {
+    fn from(val: u8) -> Self {
+        match val {
+            0 => RedisBarrierStatus::Waiting,
+            1 => RedisBarrierStatus::Done,
+            2 => RedisBarrierStatus::Leader,
+            _ => panic!("Invalid RedisBarrierStatus"),
+        }
+    }
+}
+
+/// A `BarrierWaitResult` is returned by [`Barrier::wait()`] when all systems
+/// in the [`Barrier`] have rendezvoused.
+///
+/// # Examples
+///
+/// ```
+/// use dtypes::redis::Barrier;
+///
+/// let client = redis::Client::open("redis://localhost:6379").unwrap();
+/// let mut  barrier = Barrier::new(1, "barrier_doc_test", client);
+/// let barrier_wait_result = barrier.wait();
+/// ```
+pub struct BarrierWaitResult(bool);
+
+impl BarrierWaitResult {
+    /// Returns `true` if this thread is the "leader thread" for the call to
+    /// [`Barrier::wait()`].
+    ///
+    /// Only one thread will have `true` returned from their result, all other
+    /// threads will have `false` returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use dtypes::redis::Barrier;
+    ///
+    /// let client = redis::Client::open("redis://localhost:6379").unwrap();
+    /// let mut  barrier = Barrier::new(1, "barrier_doc_test", client);
+    /// let barrier_wait_result = barrier.wait();
+    /// println!("{:?}", barrier_wait_result.is_leader());
+    /// ```
+    pub fn is_leader(&self) -> bool {
+        self.0
+    }
+}
+
+enum BarrierError {
+    RedisError(redis::RedisError),
+}
+
+impl Barrier {
+    pub fn new(num: usize, key: &str, client: redis::Client) -> Self {
+        let mut conn = client.get_connection().unwrap();
+
+        let uuid = redis::Script::new(UUID_SCRIPT)
+            .arg(&key)
+            .arg(&num)
+            .invoke::<usize>(&mut conn)
+            .expect("Failed to create barrier");
+
+        Barrier {
+            uuid: uuid,
+            num,
+            key: key.to_string(),
+            _client: client,
+            conn: Some(conn),
+        }
+    }
+
+    /// Blocks the current thread until all threads have rendezvoused here.
+    ///
+    /// Barriers are re-usable after all threads have rendezvoused once, and can
+    /// be used continuously.
+    ///
+    /// A single (arbitrary) thread will receive a [`BarrierWaitResult`] that
+    /// returns `true` from [`BarrierWaitResult::is_leader()`] when returning
+    /// from this function, and all other threads will receive a result that
+    /// will return `false` from [`BarrierWaitResult::is_leader()`].
+    ///
+    /// The barrier needs to be mutable, because it guarantees that the barrier is only used once in thread.
+    /// If you want to synchronize threads, you need to create a new barrier for each thread, so it has its own uuid.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use dtypes::redis::Barrier;
+    /// use std::thread;
+    ///
+    /// let n = 10;
+    /// let mut handles = Vec::with_capacity(n);
+    /// let client = redis::Client::open("redis://localhost:6379").unwrap();
+    /// for _ in 0..n {
+    ///     // The same messages will be printed together.
+    ///     // You will NOT see any interleaving.
+    ///     let mut barrier = Barrier::new(n, "barrier_doc_test2", client.clone());
+    ///     handles.push(thread::spawn(move|| {
+    ///         println!("before wait");
+    ///         barrier.wait();
+    ///         println!("after wait");
+    ///     }));
+    /// }
+    /// // Wait for other threads to finish.
+    /// for handle in handles {
+    ///     handle.join().unwrap();
+    /// }
+    /// ```
+    pub fn wait(&mut self) -> BarrierWaitResult {
+        let mut conn = self.conn.take().unwrap();
+        let timeout = 2;
+
+        let mut status = RedisBarrierStatus::Waiting;
+        while status == RedisBarrierStatus::Waiting {
+            status = redis::Script::new(WAITING_SCRIPT)
+                .arg(&self.key)
+                .arg(self.uuid)
+                .arg(self.num)
+                .arg(timeout)
+                .invoke::<u8>(&mut conn)
+                .expect("Failed to wait for barrier")
+                .into();
+        }
+        self.conn = Some(conn);
+
+        if status == RedisBarrierStatus::Leader {
+            BarrierWaitResult(true)
+        } else {
+            BarrierWaitResult(false)
+        }
+    }
+}
+
+impl Drop for Barrier {
+    fn drop(&mut self) {
+        let mut conn = self.conn.take().unwrap();
+        redis::Script::new(RESET_SCRIPT)
+            .arg(&self.key)
+            .arg(self.uuid)
+            .arg(self.num)
+            .invoke::<()>(&mut conn)
+            .expect("Failed to reset barrier");
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::thread;
+    use std::thread::sleep;
+
+    #[test]
+    fn test_barrier_leader() {
+        let client = redis::Client::open("redis://localhost:6379").unwrap();
+        let mut barrier = Barrier::new(1, "barrier_test_leader", client);
+        let barrier_wait_result = barrier.wait();
+        assert!(barrier_wait_result.is_leader());
+    }
+
+    #[test]
+    fn test_barrier_not_leader() {
+        let client = redis::Client::open("redis://localhost:6379").unwrap();
+
+        let mut barrier = Barrier::new(2, "barrier_test_notleader", client.clone());
+
+        let h1 = thread::spawn(move || {
+            let mut barrier = Barrier::new(2, "barrier_test_notleader", client);
+            let barrier_wait_result = barrier.wait();
+            assert!(!barrier_wait_result.is_leader());
+        });
+
+        let h2 = thread::spawn(move || {
+            sleep(std::time::Duration::from_millis(1000));
+            let barrier_wait_result = barrier.wait();
+            assert!(barrier_wait_result.is_leader());
+        });
+
+        h1.join().unwrap();
+        h2.join().unwrap();
+    }
+
+    #[test]
+    fn test_barrier_slow_check() {
+        let n = 10;
+        let mut handles = Vec::with_capacity(n);
+        let client = redis::Client::open("redis://localhost:6379").unwrap();
+        for _ in 0..n {
+            // The same messages will be printed together.
+            // You will NOT see any interleaving.
+            let mut barrier = Barrier::new(n, "barrier_doc_test2", client.clone());
+            handles.push(thread::spawn(move || barrier.wait().is_leader()));
+        }
+        // Wait for other threads to finish.
+        assert_eq!(
+            handles
+                .into_iter()
+                .map(|h| h.join().unwrap())
+                .map(|x| if x { 1 } else { 0 })
+                .sum::<i32>(),
+            1
+        );
+    }
+
+    #[test]
+    fn test_barrier_reuse() {
+        let client = redis::Client::open("redis://localhost:6379").unwrap();
+
+        let mut barrier = Barrier::new(1, "barrier_test_reuse", client.clone());
+        barrier.wait();
+        let mut barrier = Barrier::new(1, "barrier_test_reuse", client.clone());
+        barrier.wait();
+    }
+}

src/redis/mod.rs

@@ -41,6 +41,7 @@
 //!
 //! It is possible to implement your own complex types by implementing the [BackedType](crate::BackedType) trait.
 //! But it should not be needed as long as your type implements some or all of the various [Ops](https://doc.rust-lang.org/std/ops/index.html) traits.
+mod barrier;
 mod bool_type;
 mod clock;
 mod generic;
@@ -53,6 +54,7 @@ mod string;
 
 pub(crate) use helper::apply_operator;
 
+pub use barrier::{Barrier, BarrierWaitResult};
 pub use bool_type::TBool as Dbool;
 pub use clock::ClockOrdered;
 pub use generic::Generic;