From 2d2998c08de980bb7f8b6a1ad5cda0a16fcd563d Mon Sep 17 00:00:00 2001
From: Davin McCall <davmac@davmac.org>
Date: Sat, 10 Feb 2018 15:32:51 +0000
Subject: [PATCH] control conn. allocate_service_handle(): exception safety.

---
 src/control.cc | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/src/control.cc b/src/control.cc
index 85a70ec..fd89e20 100644
--- a/src/control.cc
+++ b/src/control.cc
@@ -292,6 +292,8 @@ bool control_conn_t::list_services()
 
 control_conn_t::handle_t control_conn_t::allocate_service_handle(service_record *record)
 {
+    // Try to find a unique handle (integer) in a single pass. Start with 0, and keep track of the largest
+    // handle seen so far. If we find the current candidate, we set the candidate to (largest+1).
     bool is_unique = true;
     handle_t largest_seen = 0;
     handle_t candidate = 0;
@@ -303,14 +305,25 @@ control_conn_t::handle_t control_conn_t::allocate_service_handle(service_record
         }
         is_unique &= (p.second != record);
     }
-    
-    keyServiceMap[candidate] = record;
-    serviceKeyMap.insert(std::make_pair(record, candidate));
-    
+
+    // The following operations perform allocation (can throw std::bad_alloc). If an exception occurs we
+    // must undo any previous actions:
     if (is_unique) {
         record->add_listener(this);
     }
     
+    try {
+        keyServiceMap[candidate] = record;
+        serviceKeyMap.insert(std::make_pair(record, candidate));
+    }
+    catch (...) {
+        if (is_unique) {
+            record->remove_listener(this);
+        }
+
+        keyServiceMap.erase(candidate);
+    }
+    
     return candidate;
 }
 
-- 
2.25.1