From c94551f816e3cac6200558bdd2b7774f8ad41af4 Mon Sep 17 00:00:00 2001
From: Brian Seymour <imbrianseymour@gmail.com>
Date: Thu, 20 Apr 2017 20:39:29 -0700
Subject: [PATCH] possible cause of observed deadlock: removed possibility of
 communicating over the idle_workers channel with a lock and ending up in
 closenotify case causing a deadlock

---
 src/dispenserd/queue.go   |  1 +
 src/dispenserd/service.go | 13 ++++++++++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/dispenserd/queue.go b/src/dispenserd/queue.go
index 463dbbb..8b70965 100644
--- a/src/dispenserd/queue.go
+++ b/src/dispenserd/queue.go
@@ -132,6 +132,7 @@ func InsertJob(job job) {
     }
 
     if idle_workers[lane] > 0 {
+        mu.Unlock()
         listeners[lane] <- 1
     } else {
         mu.Unlock()
diff --git a/src/dispenserd/service.go b/src/dispenserd/service.go
index f133ce8..e11a337 100644
--- a/src/dispenserd/service.go
+++ b/src/dispenserd/service.go
@@ -9,7 +9,6 @@ import (
 )
 
 var listeners = map[string]chan int{"main": make(chan int)}
-var ready = make(chan int)
 
 type generic_payload struct {
     Status  string `json:"status"`
@@ -209,16 +208,24 @@ func ServiceReceiveBlock(res http.ResponseWriter, req *http.Request) {
         for {
             select {
             case <-listeners[current_lane]:
-                if len(queue[current_lane]) == 0 {
+                mu.Lock()
+
+                // empty queue or no workers means do nothing
+                if len(queue[current_lane]) == 0 || idle_workers[current_lane] == 0 {
                     mu.Unlock()
                     continue
                 }
+
                 idle_workers[current_lane] -= 1
+
                 send_job()
+
                 return
             case <-cn.CloseNotify():
                 mu.Lock()
-                idle_workers[current_lane] -= 1
+                if idle_workers[current_lane] > 0 {
+                    idle_workers[current_lane] -= 1
+                }
                 mu.Unlock()
 
                 return