From fdbfda848fc8265fadb9deca5e40ae8c9748d9c1 Mon Sep 17 00:00:00 2001
From: Mathew Sutcliffe <oktal3700@gmail.com>
Date: Tue, 4 Jul 2017 23:06:59 +0100
Subject: [PATCH] T102 Don't try to wait for a worker to finish while holding a
 lock on the mutex that protects its finished flag, as it will deadlock.

---
 src/blackcore/db/backgrounddataupdater.cpp | 8 +++++++-
 src/blackmisc/worker.h                     | 6 +++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/blackcore/db/backgrounddataupdater.cpp b/src/blackcore/db/backgrounddataupdater.cpp
index bd97427cc..9a5b45ff0 100644
--- a/src/blackcore/db/backgrounddataupdater.cpp
+++ b/src/blackcore/db/backgrounddataupdater.cpp
@@ -75,7 +75,13 @@ namespace BlackCore
             m_enabled = false;
             if (!CThreadUtils::isCurrentThreadObjectThread(this))
             {
-                doIfNotFinished([this] { this->abandonAndWait(); });
+                std::promise<void> promise;
+                doIfFinishedElse([&promise] { promise.set_value(); }, [&promise, this]
+                {
+                    this->then([&promise] { promise.set_value(); });
+                    this->abandon();
+                });
+                promise.get_future().wait();
             }
         }
 
diff --git a/src/blackmisc/worker.h b/src/blackmisc/worker.h
index adf1d7e6d..2bde3c043 100644
--- a/src/blackmisc/worker.h
+++ b/src/blackmisc/worker.h
@@ -134,7 +134,7 @@ namespace BlackMisc
         }
 
         //! Executes some code (in the caller's thread) if the task has not finished.
-        //! \threadsafe
+        //! \threadsafe But the functor will deadlock if it waits for the task to finish.
         template <typename F>
         void doIfNotFinished(F functor) const
         {
@@ -142,8 +142,8 @@ namespace BlackMisc
             if (! m_finished) { functor(); }
         }
 
-        //! Executes some code (in the caller's thread) if the task has not finished and some different code if it has finished.
-        //! \threadsafe
+        //! Executes some code (in the caller's thread) if the task has finished and some different code if it has not finished.
+        //! \threadsafe But the elseFunctor will deadlock if it waits for the task to finish.
         template <typename F1, typename F2>
         void doIfFinishedElse(F1 ifFunctor, F2 elseFunctor) const
         {