Fix possibly fatal race condition when calling OnDelete()

This function could be called on an already deleted object, which could
result in a crash, and always resulted in a TSAN error.

Fix this by calling it before releasing the internal lock, which
prevents this from happening, but will result in a deadlock if this
function is overridden to do something requiring any lock held by the
thread.

This is not ideal, but still seems to be like a lesser evil.

interface/wx/thread.h

@@ -486,8 +486,10 @@ public:
         will be executed in the context of the thread that called Delete() and
         <b>not</b> in this thread's context.
 
-        TestDestroy() will be true for the thread before OnDelete() gets
-        executed.
+        Note that TestDestroy() will block until OnDelete() returns, so this
+        function should return as quickly as possible and definitely shouldn't
+        perform any GUI actions nor try acquiring any locks, as this could
+        easily result in a deadlock.
 
         @since 2.9.2
 

src/unix/threadpsx.cpp

@@ -1575,10 +1575,16 @@ wxThreadError wxThread::Delete(ExitCode *rc, wxThreadWait WXUNUSED(waitMode))
     // ask the thread to stop
     m_internal->SetCancelFlag();
 
-    m_critsect.Leave();
-
+    // Normally we should never call out while holding the lock (on m_critsect
+    // in this case), but we can't do it later because as soon as we unlock it,
+    // this object may be destroyed as the thread executing its Entry() may
+    // call TestDestroy() and decide to exit at any moment, so we have to do it
+    // now and hope that OnDelete() doesn't do anything stupid (or, preferably,
+    // anything at all).
     OnDelete();
 
+    m_critsect.Leave();
+
     switch ( state )
     {
         case STATE_NEW: