Fix using wxHTTP and wxFTP from worker thread in Unix ports.

This backports e18c8fd29a,
d421373c2e and
6c43aa90b6 from master to avoid crashes when
using wxHTTP or wxFTP from threads other than main.

See #17031.

samples/sockets/client.cpp

@@ -31,6 +31,7 @@
 #include "wx/socket.h"
 #include "wx/url.h"
 #include "wx/sstream.h"
+#include "wx/thread.h"
 #include <memory>
 
 // --------------------------------------------------------------------------
@@ -575,23 +576,13 @@ void MyFrame::OnDatagram(wxCommandEvent& WXUNUSED(event))
 
 #if wxUSE_URL
 
-void MyFrame::OnTestURL(wxCommandEvent& WXUNUSED(event))
+void DoDownload(const wxString& urlname)
 {
-    // Ask for the URL
-    static wxString s_urlname("http://www.google.com/");
-    wxString urlname = wxGetTextFromUser
-                       (
-                        _("Enter an URL to get"),
-                        _("URL:"),
-                        s_urlname
-                       );
-    if ( urlname.empty() )
-        return; // cancelled by user
+    wxString testname("URL");
+    if ( !wxIsMainThread() )
+        testname += " in worker thread";
 
-    s_urlname = urlname;
-
-
-    TestLogger logtest("URL");
+    TestLogger logtest(testname);
 
     // Parse the URL
     wxURL url(urlname);
@@ -626,6 +617,51 @@ void MyFrame::OnTestURL(wxCommandEvent& WXUNUSED(event))
                  urlname, sout.GetString());
 }
 
+void MyFrame::OnTestURL(wxCommandEvent& WXUNUSED(event))
+{
+    // Ask for the URL
+    static wxString s_urlname("http://www.google.com/");
+    wxString urlname = wxGetTextFromUser
+                       (
+                        _("Enter an URL to get"),
+                        _("URL:"),
+                        s_urlname
+                       );
+    if ( urlname.empty() )
+        return; // cancelled by user
+
+    s_urlname = urlname;
+
+    // First do it in this thread.
+    DoDownload(urlname);
+
+    // And then also in a worker thread.
+#if wxUSE_THREADS
+    class DownloadThread : public wxThread
+    {
+    public:
+        explicit DownloadThread(const wxString& url): m_url(url)
+        {
+            Run();
+        }
+
+        virtual void* Entry() wxOVERRIDE
+        {
+            DoDownload(m_url);
+
+            return NULL;
+        }
+
+    private:
+        const wxString m_url;
+    };
+
+    // NB: there is a race condition here, we don't check for this thread
+    // termination before exiting the application, don't do this in real code!
+    new DownloadThread(urlname);
+#endif // wxUSE_THREADS
+}
+
 #endif // wxUSE_URL
 
 void MyFrame::OnSocketEvent(wxSocketEvent& event)