From f5afdd91a5190250ed0916b606652c07a70b2c73 Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@koefferlein.de>
Date: Mon, 10 May 2021 23:42:40 +0200
Subject: [PATCH] Preventing event recursion on different levels.

---
 src/lay/lay/layApplication.cc |  5 +++++
 src/lay/lay/layMainWindow.h   |  8 ++++++++
 src/tl/tl/tlLog.cc            | 15 ++++++++++++---
 src/tl/tl/tlLog.h             |  1 +
 4 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/lay/lay/layApplication.cc b/src/lay/lay/layApplication.cc
index 76a9000cd..31998ed02 100644
--- a/src/lay/lay/layApplication.cc
+++ b/src/lay/lay/layApplication.cc
@@ -1486,6 +1486,11 @@ GuiApplication::process_events_impl (QEventLoop::ProcessEventsFlags flags, bool
 {
   if (mp_mw) {
 
+    //  prevent recursive process_events
+    if (mp_mw->is_busy ()) {
+      return;
+    }
+
     if (silent && tl::DeferredMethodScheduler::instance ()) {
       tl::DeferredMethodScheduler::instance ()->enable (false);
     }
diff --git a/src/lay/lay/layMainWindow.h b/src/lay/lay/layMainWindow.h
index b5e37b283..20397b9f0 100644
--- a/src/lay/lay/layMainWindow.h
+++ b/src/lay/lay/layMainWindow.h
@@ -408,6 +408,14 @@ public:
     m_busy = bm;
   }
 
+  /**
+   *  @brief Returns true if the application is busy
+   */
+  bool is_busy () const
+  {
+    return m_busy;
+  }
+
   /**
    *  @brief Enable synchronous mode or disable it
    *
diff --git a/src/tl/tl/tlLog.cc b/src/tl/tl/tlLog.cc
index bfb5aafc9..1cebcb011 100644
--- a/src/tl/tl/tlLog.cc
+++ b/src/tl/tl/tlLog.cc
@@ -67,7 +67,7 @@ verbosity ()
 //  Channel implementation
 
 Channel::Channel ()
-  : m_no_endl (false), m_active (false)
+  : m_no_endl (false), m_active (false), m_in_yield (false)
 {
   //  .. nothing else ..
 }
@@ -98,10 +98,19 @@ Channel::release_proxy ()
   end ();
   m_active = false;
   m_no_endl = false;
+  bool in_yield = m_in_yield;
+  m_in_yield = true;
   m_lock.unlock ();
 
-  //  after we have released the lock we give the receivers an opportunity to process events
-  yield ();
+  //  after we have released the lock we give the receivers an opportunity to process events. Note that we allow only one thread to yield
+  //  at the same time and no recursive yields.
+  if (! in_yield) {
+    yield ();
+    //  this should be atomic, but execution reordering may place it before yield(). Hence the lock.
+    m_lock.lock ();
+    m_in_yield = false;
+    m_lock.unlock ();
+  }
 }
 
 ChannelEndl endl;
diff --git a/src/tl/tl/tlLog.h b/src/tl/tl/tlLog.h
index b085a14b7..775222c29 100644
--- a/src/tl/tl/tlLog.h
+++ b/src/tl/tl/tlLog.h
@@ -154,6 +154,7 @@ private:
 
   bool m_no_endl;
   bool m_active;
+  bool m_in_yield;
 };
 
 /**