From a0c52fa425beedb9372f26218a47bc2cf1130ca9 Mon Sep 17 00:00:00 2001
From: Richard Newman <rnewman@twinql.com>
Date: Wed, 14 Mar 2018 08:18:22 -0700
Subject: [PATCH] NON-WORKING: can't spawn a thread because the closure would
 outlive reports.

---
 db/src/tx_observer.rs | 56 +++++++++++++++++++++++--------------------
 1 file changed, 30 insertions(+), 26 deletions(-)

diff --git a/db/src/tx_observer.rs b/db/src/tx_observer.rs
index d2011294..dbaee0a5 100644
--- a/db/src/tx_observer.rs
+++ b/db/src/tx_observer.rs
@@ -24,27 +24,30 @@ use types::{
 };
 
 pub struct TxObserver {
-    notify_fn: Arc<Box<Fn(&String, &Vec<Arc<TxReport>>) + Send + Sync>>,
+    notify_fn: Arc<Box<Fn(&String, &Vec<&TxReport>) + Send + Sync>>,
     attributes: AttributeSet,
 }
 
 impl TxObserver {
-    pub fn new<F>(attributes: AttributeSet, notify_fn: F) -> TxObserver where F: Fn(&String, &Vec<Arc<TxReport>>) + 'static + Send + Sync {
+    pub fn new<F>(attributes: AttributeSet, notify_fn: F) -> TxObserver where F: Fn(&String, &Vec<&TxReport>) + 'static + Send + Sync {
         TxObserver {
             notify_fn: Arc::new(Box::new(notify_fn)),
             attributes,
         }
     }
 
-    pub fn applicable_reports(&self, reports: &Vec<Arc<TxReport>>) -> Vec<Arc<TxReport>> {
-        reports.into_iter().filter_map( |report| {
-            self.attributes.intersection(&report.changeset)
-                           .next()
-                           .and_then(|_| Some(Arc::clone(report)))
-        }).collect()
+    pub fn applicable_reports<'r>(&self, reports: &'r Vec<TxReport>) -> Vec<&'r TxReport> {
+        let mut out = Vec::with_capacity(reports.len());
+        for report in reports {
+            if self.attributes.intersection(&report.changeset).next().is_none() {
+                continue;
+            }
+            out.push(report);
+        }
+        out
     }
 
-    fn notify(&self, key: &String, reports: &Vec<Arc<TxReport>>) {
+    fn notify(&self, key: &String, reports: &Vec<&TxReport>) {
         (*self.notify_fn)(key, reports);
     }
 }
@@ -53,14 +56,14 @@ pub trait Command {
     fn execute(&mut self);
 }
 
-pub struct NotifyTxObserver {
+pub struct NotifyTxObserver<'r> {
     key: String,
-    reports: Vec<Arc<TxReport>>,
+    reports: Vec<&'r TxReport>,
     observer: Weak<TxObserver>,
 }
 
-impl NotifyTxObserver {
-    pub fn new(key: String, reports: Vec<Arc<TxReport>>, observer: Weak<TxObserver>) -> Self {
+impl<'r> NotifyTxObserver<'r> {
+    pub fn new(key: String, reports: Vec<&'r TxReport>, observer: Weak<TxObserver>) -> Self {
         NotifyTxObserver {
             key,
             reports,
@@ -69,17 +72,17 @@ impl NotifyTxObserver {
     }
 }
 
-impl Command for NotifyTxObserver {
+impl<'r> Command for NotifyTxObserver<'r> {
     fn execute(&mut self) {
         self.observer.upgrade().map(|o| o.notify(&self.key, &self.reports));
     }
 }
 
-pub struct AsyncBatchExecutor {
-    commands: Vec<Box<Command + Send>>,
+pub struct AsyncBatchExecutor<'r> {
+    commands: Vec<Box<Command + Send + 'r>>,
 }
 
-impl Command for AsyncBatchExecutor {
+impl<'r> Command for AsyncBatchExecutor<'r> {
     fn execute(&mut self) {
         // need to clone to move to a new thread.
         let command_queue = ::std::mem::replace(&mut self.commands, Vec::new());
@@ -121,8 +124,8 @@ impl TxObservationService {
         !self.observers.is_empty()
     }
 
-    fn command_from_reports(&self, key: &String, reports: &Vec<Arc<TxReport>>, observer: &Arc<TxObserver>) -> Option<Box<Command + Send>> {
-        let applicable_reports = observer.applicable_reports(reports);
+    fn command_from_reports<'r>(&self, key: &String, reports: &'r Vec<TxReport>, observer: &Arc<TxObserver>) -> Option<Box<Command + Send + 'r>> {
+        let applicable_reports: Vec<&'r TxReport> = observer.applicable_reports(reports);
         if !applicable_reports.is_empty() {
             Some(Box::new(NotifyTxObserver::new(key.clone(), applicable_reports, Arc::downgrade(observer))))
         } else {
@@ -130,13 +133,14 @@ impl TxObservationService {
         }
     }
 
-    pub fn transaction_did_commit(&mut self, reports: Vec<Arc<TxReport>>) {
-        // notify all observers about their relevant transactions
-        let commands: Vec<Box<Command + Send>> = self.observers
-                                                     .iter()
-                                                     .filter_map(|(key, observer)| { self.command_from_reports(&key, &reports, &observer) })
-                                                     .collect();
-        self.command_queue.push(Box::new(AsyncBatchExecutor{ commands }));
+    pub fn transaction_did_commit(&mut self, reports: Vec<TxReport>) {
+        let mut commands = Vec::with_capacity(self.observers.len());
+        for (key, observer) in self.observers.iter() {
+            if let Some(command) = self.command_from_reports(key, &reports, &observer) {
+                commands.push(command);
+            }
+        }
+        self.command_queue.push(Box::new(AsyncBatchExecutor { commands }));
     }
 
     pub fn run(&mut self) {