From 61507ec1fa61fe134547a7eac9541375c6215b33 Mon Sep 17 00:00:00 2001
From: David Blajda <blajda@hotmail.com>
Date: Thu, 20 Dec 2018 00:09:49 +0000
Subject: Replace channel based barrier with shared future based barrier

---
 src/sync/barrier.rs | 143 +++++++++++-----------------------------------------
 src/sync/waiter.rs  |  12 ++---
 2 files changed, 36 insertions(+), 119 deletions(-)

(limited to 'src/sync')

diff --git a/src/sync/barrier.rs b/src/sync/barrier.rs
index 7e53b12..c0f21b8 100644
--- a/src/sync/barrier.rs
+++ b/src/sync/barrier.rs
@@ -1,130 +1,47 @@
 use super::waiter::Waiter;
-use futures::sync::mpsc;
-use futures::sync::oneshot;
 use futures::prelude::*;
+use std::sync::{Arc, Mutex};
+use futures::future::{Shared, SharedError};
 
-pub trait BarrierSync<W: Waiter> {
-    fn wait_for(&mut self, waiter: W) -> Box<Future<Item=W::Item, Error=W::Error> + Send>;
-}
+use crate::error::ConditionError;
 
-pub struct Barrier<W: Waiter> {
-    sink: Option<mpsc::Sender<(W, oneshot::Sender<Result<W::Item, W::Error>>)>>,
+#[derive(Clone)]
+pub struct Barrier {
+    inner: Arc<Mutex<BarrierRef>>,
 }
 
-impl<W: Waiter + 'static + Send> BarrierSync<W> for Barrier<W> {
-    fn wait_for(&mut self, waiter: W) -> Box<Future<Item=W::Item, Error=W::Error> + Send> {
-        let (resp_tx, resp_rx) = oneshot::channel();
-
-        if self.sink.is_none() {
-            let (barrier_tx, barrier_rx) = mpsc::channel(40); 
-            self.barrier_task(barrier_rx);
-            self.sink.replace(barrier_tx);
-        }
-
-        let chan = self.sink.as_mut().unwrap().clone();
-
-        /*TODO: I want meaningful error types... */
-        let f1 = chan
-            .send((waiter, resp_tx))
-            .map_err(|err| W::Error::from(()))
-            .and_then(|_| {
-                resp_rx.then(|result| {
-                    match result {
-                        Ok(Ok(result)) => Ok(result),
-                        Ok(Err(err)) => Err(err),
-                        Err(err) => Err(W::Error::from(())),
-                    }
-                })
-            });
-
-        Box::new(f1)
-    }
+struct BarrierRef {
+    condition: Option<Shared<Box<Future<Item=(), Error=ConditionError> + Send>>>
 }
 
-impl<W: Waiter + 'static + Send> Barrier<W> {
-    pub fn new() -> Barrier<W> {
+impl Barrier {
+
+    pub fn new() -> Barrier {
         Barrier {
-            sink: None,
+            inner: Arc::new(Mutex::new(
+            BarrierRef {
+                condition: None,
+            }))
         }
     }
 
-    fn barrier_task(&self, receiver: mpsc::Receiver<(W, oneshot::Sender<Result<W::Item, W::Error>>)>) {
-
-        enum Message<W: Waiter> {
-            Request((W, oneshot::Sender<Result<<W as Waiter>::Item, <W as Waiter>::Error>>)),
-            OnCondition(Result<(), <W as Waiter>::ConditionError>),
-        }
+    pub fn condition(&self, waiter: &impl Waiter) 
+        -> Shared<Box<Future<Item=(), Error=ConditionError> + Send>> 
+    {
+        let mut mut_barrier = self.inner.lock().unwrap();
+        let maybe_condition = &mut mut_barrier.condition;
 
-        let mut polling = false;
-        let (on_condition_tx, on_condition_rx) = mpsc::unbounded();
-        let mut waiters = Vec::new();
-        let f1 = receiver.map(|request| Message::Request(request));
-        let f2 = on_condition_rx.map(|result| Message::OnCondition(result));
+        let f = maybe_condition.get_or_insert_with(|| {
+            waiter.condition()
+        });
 
-        let inner_condition = on_condition_tx.clone();
         let f =
-            f1.select(f2).for_each(move |message| {
-            match message {
-                Message::Request((waiter, backchan)) => {
-                    if waiter.blocked() && !polling {
-                        println!("locked");
-
-                        let c1 = inner_condition.clone();
-                        let f = waiter
-                            .condition_poller()
-                            .map(|_| ())
-                            .then(|result| {
-                                c1.send(result).wait();
-                                Ok(())
-                            });
-                        tokio::spawn(f);
-                        polling = true;
-
-                        waiters.push((waiter, backchan));
-                    } else if waiter.blocked() || polling {
-                        println!("polling");
-                        waiters.push((waiter, backchan));
-                    } else {
-                        println!("Pass along waiter!");
-                        let f = waiter.into_future()
-                            .then(|res| {
-                                backchan.send(res);
-                                Ok(())
-                            });
-
-                        tokio::spawn(f);
-                    }
-                },
-                Message::OnCondition(result) => {
-                    polling = false;
-                    /*Resubmit all waiters back to the request channel
-                     * At least one waiter will pass the barrier
-                     */
-                    match result {
-                        Ok(_) => {
-                            while waiters.len() > 0 {
-                                let (waiter, backchan) = waiters.pop().unwrap();
-                                let f = waiter.into_future()
-                                    .then(|res| {
-                                        backchan.send(res);
-                                        Ok(())
-                                    });
-
-                                tokio::spawn(f);
-                            }
-                        }, 
-                        _ => { panic!("condition channel closed") }
-                    }
-                }
-            }
-
-
-
-            Ok(()) 
-        })
-        .map(|_| ())
-        .map_err(|_| ());
-
-    tokio::spawn(f);
+            if let Some(_) = f.peek() {
+                let condition = waiter.condition();
+                maybe_condition.replace(condition);
+                maybe_condition.as_ref().unwrap()
+            } else { f };
+        f.clone()
     }
 }
+
diff --git a/src/sync/waiter.rs b/src/sync/waiter.rs
index 656c42e..8039280 100644
--- a/src/sync/waiter.rs
+++ b/src/sync/waiter.rs
@@ -1,13 +1,13 @@
 use futures::sync::oneshot;
 use futures::Future;
+use futures::future::{Shared, SharedError};
+use crate::error::ConditionError;
 
 pub trait Waiter {
-    type Item: Send + 'static;
-    type Error: From<Self::ConditionError> 
-        + From<oneshot::Canceled> + From<()> + Send + 'static;
-    type ConditionError: Send + Clone + 'static;
+    type Item: Default;
+    type Error: From<SharedError<ConditionError>>; 
 
     fn blocked(&self) -> bool;
-    fn condition_poller(&self) -> Box<Future<Item=(), Error=Self::ConditionError> + Send>;
-    fn into_future(self) -> Box<Future<Item=Self::Item, Error=Self::Error> + Send>;
+    fn condition(&self) 
+        -> Shared<Box<Future<Item=(), Error=ConditionError> + Send>>;
 }
-- 
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