don't fiddle with thread structs that were not initialized yet (#6979)

lib/Basics/Thread.cpp

@@ -138,6 +138,7 @@ std::string Thread::stringify(ThreadState state) {
 /// @brief constructs a thread
 Thread::Thread(std::string const& name, bool deleteOnExit)
     : _deleteOnExit(deleteOnExit),
+      _threadStructInitialized(false),
       _name(name),
       _thread(),
       _threadNumber(0),
@@ -155,12 +156,14 @@ Thread::~Thread() {
       << "delete(" << _name << "), state: " << stringify(state);
 
   if (state == ThreadState::STOPPED) {
-    if (TRI_IsSelfThread(&_thread)) {
-      // we must ignore any errors here, but TRI_DetachThread will log them
-      TRI_DetachThread(&_thread);
-    } else {
-      // we must ignore any errors here, but TRI_JoinThread will log them
-      TRI_JoinThread(&_thread);
+    if (_threadStructInitialized) {
+      if (TRI_IsSelfThread(&_thread)) {
+        // we must ignore any errors here, but TRI_DetachThread will log them
+        TRI_DetachThread(&_thread);
+      } else {
+        // we must ignore any errors here, but TRI_JoinThread will log them
+        TRI_JoinThread(&_thread);
+      }
     }
 
     _state.store(ThreadState::DETACHED);
@@ -282,6 +285,9 @@ bool Thread::start(ConditionVariable* finishedCondition) {
     return false;
   }
 
+  TRI_ASSERT(!_threadStructInitialized);
+  memset(&_thread, 0, sizeof(thread_t));
+
   bool ok =
       TRI_StartThread(&_thread, &_threadId, _name.c_str(), &startThread, this);
 
@@ -295,6 +301,8 @@ bool Thread::start(ConditionVariable* finishedCondition) {
     cleanupMe();
   }
 
+  _threadStructInitialized = true;
+
   return ok;
 }
 

lib/Basics/Thread.h

@@ -151,6 +151,7 @@ class Thread {
 
  private:
   bool const _deleteOnExit;
+  bool _threadStructInitialized;
 
   // name of the thread
   std::string const _name;